U.S. patent application number 13/346569 was filed with the patent office on 2012-12-20 for data processing for real-time tracking of a target in radiation therapy.
Invention is credited to Steven C. Dimmer, Stephen C. Phillips, Ryan K. Seghers, J. Nelson Wright.
Application Number | 20120323062 13/346569 |
Document ID | / |
Family ID | 36317240 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120323062 |
Kind Code |
A1 |
Wright; J. Nelson ; et
al. |
December 20, 2012 |
DATA PROCESSING FOR REAL-TIME TRACKING OF A TARGET IN RADIATION
THERAPY
Abstract
A facility for processing data is described. The facility
receives a stream of digital location indications, each location
indication identifying a location of a patient while undergoing
radiation therapy. In response to each location indication of the
string, in substantially real-time relative to the receipt of the
position indication, the facility performs an action responsive to
the location indication.
Inventors: |
Wright; J. Nelson; (Mercer
Island, WA) ; Dimmer; Steven C.; (Bellevue, WA)
; Phillips; Stephen C.; (Woodinville, WA) ;
Seghers; Ryan K.; (Kirkland, WA) |
Family ID: |
36317240 |
Appl. No.: |
13/346569 |
Filed: |
January 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11190205 |
Jul 25, 2005 |
8095203 |
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13346569 |
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60590693 |
Jul 23, 2004 |
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Current U.S.
Class: |
600/1 |
Current CPC
Class: |
A61B 2090/3958 20160201;
A61N 5/1049 20130101; A61N 2005/1051 20130101; A61N 5/107
20130101 |
Class at
Publication: |
600/1 |
International
Class: |
A61N 5/10 20060101
A61N005/10 |
Claims
1. A method in a computing system for processing data, comprising:
receiving a stream of digital location indications, each location
indication identifying a location of a target in a human patient
using a marker secured in the patient such that the marker is
substantially fixed relative to the target; and in response to each
location indication of the stream, in substantially real-time
relative to the receipt of the position indication, performing an
action responsive to the location indication.
2. The method of claim 1 wherein each received location indication
indicates a location occupied by the target substantially
immediately before the location indication is received.
3. The method of claim 1 wherein each location indication indicates
a location of the target in three dimensions.
4. The method of claim 1 each location indication represents a
vector from a machine isocenter point.
5. The method of claim 1 wherein each location indication is based
upon interrogation of a plurality of passive magnetic markers
attached to the target.
6. The method of claim 1 wherein each location indication indicates
a relative location that is relative to a target location located
with respect to a plurality of target-attached markers.
7. The method of claim 1 wherein each location indication indicates
the position of a predetermined radiation treatment site of the
target.
8. The method of claim 1 wherein each location indication indicates
the location of the target relative to a location within one or
more paths established for the propagation of radiation energy.
9. The method of claim 1 wherein the performed action comprises
augmenting a displayed graph of locations to include the location
indicated by the location indication.
10. The method of claim 9 wherein radiation therapy is performed in
a radiation therapy enclosure, and wherein the augmented graph is
displayed on a device outside the radiation therapy enclosure.
11. The method of claim 1 wherein the performed action comprises
persistently storing information reflecting the location indicated
by the location indication.
12. The method of claim 1 and wherein each location indication of
the received stream of digital location indications identifies the
location of the target while the target is undergoing radiation
therapy, and wherein the performed action comprises: determining
whether the location indicated by the location indication merits
modifying a parameter of the radiation treatment; and where the
location indicated by the location indication merits modifying a
parameter of the radiation treatment, performing a mid-treatment
modification to a parameter of the radiation treatment in
accordance with the location indicated by location indication.
13. The method of claim 12 wherein the radiation treatment has at
least one beam shape parameter specifying a cross-sectional shape
of a radiation beam to be projected toward the target, and wherein
the performed modification is to the beam shape parameter.
14. The method of claim 12 wherein the radiation treatment has a
beam direction parameter specifying a direction in which a
radiation beam is projected toward the target, and wherein the
performed modification is to the beam direction parameter.
15. The method of claim 12 wherein the radiation treatment has an
intensity parameter specifying a radiation intensity with which the
target is to be treated, and wherein the performed modification is
to the intensity parameter.
16. The method of claim 12 wherein the radiation treatment has at
least one couch location parameter specifying a location of the
couch bearing the target relative to the radiation treatment, and
wherein the performed modification is to the couch location
parameter.
17. The method of claim 12 wherein the radiation treatment has at
least one couch orientation parameter specifying a orientation of
the couch bearing the target relative to the radiation treatment,
and wherein the performed modification is to the couch orientation
parameter.
18. The method of claim 1 wherein the performed action comprises:
comparing the location indicated by the location indication with a
predefined volume; and where the location indicated by the location
indication falls outside the predefined volume, presenting a
warning.
19. The method of claim 18 wherein the warning is an audible
warning.
20. The method of claim 18 wherein the warning is a visual
warning.
21. The method of claim 18 wherein the warning is a redundant
visual warning.
22. The method of claim 20 wherein the warning is displayed in a
manner designed to warn a technician.
23. The method of claim 20 wherein the warning is displayed in a
manner designed to warn the target.
24. The method of claim 1 wherein the performed action comprises:
comparing the location indicated by the location indication with a
predefined volume; and where the location indicated by the location
indication falls outside the predefined volume, suspending
radiation treatment in process during the receipt of the
stream.
25. The method of claim 1 wherein the received stream of digital
location indications is obtained using one or more markers attached
to the target.
26. The method of claim 1 wherein the received stream of digital
location indications is obtained using one or more markers
implanted subcutaneously in the target.
27. The method of claim 1 wherein the received stream of digital
location indications has a frequency of at least 20 hertz.
28. The method of claim 1 wherein the received stream of digital
location indications has a latency of no more than 50
milliseconds.
29. The method of claim 1 wherein the received stream of digital
location indications has a latency of no more than 200
milliseconds.
30. The method of claim 1 wherein the stream of digital location
indications is received at a rate that permits the location of the
marker to be tracked with an area that does not exceed a threshold
of five millimeters.
31. The method of claim 1 wherein the action responsive to each
location indication of the stream is performed in substantially
real-time relative to a measurement time associated with performing
measurements upon which the position indication is based.
32. A computing system for processing data, comprising: a data
receiver subsystem that receives a stream of digital location
indications, each location indication identifying a location of a
target in a human patient using a marker secured in the patient
such that the marker is substantially fixed relative to the target,
the digital location indications being based upon locating the
marker using non-ionizing radiation; and a data processing
subsystem that, in response to each location indication of the
stream, in substantially real-time relative to the receipt of the
position indication by the data receiver subsystem, performs an
action responsive to the location indication.
33. A computer-readable medium whose contents cause a computing
system to perform a method for processing data, comprising:
receiving a digital location indication target in a human patient
using a marker secured in the patient such that the marker is
substantially fixed relative to the target, the digital location
indications being based upon locating the marker using non-ionizing
radiation; and in response to receiving the location indication, in
substantially real-time relative to the receipt of the position
indication, performing an action responsive to the location
indication.
34. The computer-readable medium of claim 32 wherein the action is
performed in substantially real-time relative to a measurement time
associated with a measurement upon which the position indication is
based.
35. One or more computer memories collectively containing a target
tracking data structure, comprising: a plurality of digital
location indications, each location indication identifying a
location of a target while undergoing radiation therapy, the
location indications having been received in a stream substantially
in real-time relative to their measurement.
36. One or more generated data signals collectively conveying a
target tracking data structure, comprising: a plurality of digital
location indications, each location indication identifying a
location of a target in a human patient using a marker secured in
the patient such that the marker is substantially fixed relative to
the target, the location indications having been received in a
stream substantially in real-time relative to their
measurement.
37. A method in a computing system for verifying a radiation
therapy session, comprising: reading a stored set of digital
location indications each identifying a location of a target while
undergoing radiation therapy during a distinguished therapy
session; and using the read digital location indications to review
the provision of radiation therapy during the distinguished therapy
session.
38. The method of claim 37 wherein reviewing the provision of
radiation therapy during the distinguished radiation therapy
session comprises verifying the radiation therapy session was
conducted in accordance with a distinguished radiation therapy
plan.
39. The method of claim 37 wherein the verification involves:
correlating the location indications with time-indexed information
about treatment parameters; and using the correlated information to
determine that the radiation therapy was conducted in accordance
with a radiation therapy plan.
40. The method of claim 37 wherein reviewing the provision of
radiation therapy during the distinguished therapy session
comprises displaying an indication of the location of the target
throughout the distinguished therapy session.
41. The method of claim 37 wherein reviewing the provision of
radiation therapy during the distinguished therapy session
comprises determining a portion of the distinguished therapy
session during which the target location was outside a predefined
volume.
42. The method of claim 37 wherein reviewing the provision of
radiation therapy during the distinguished therapy session
comprises identifying the smallest volume containing all of the
target locations.
43. The method of claim 37, further comprising: reading a set of
digital location indications for one or more patient-implanted
markers from which the digital locations each identifying a
location of the target were derived; and generating a revised set
of digital location indications each identifying a location of the
target based upon a relationship between the location of the target
and the locations of the markers other than was used to generate
the read set of digital location indications each identifying the
location of the target.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. patent
application Ser. No. 60/590,693 filed Jul. 23, 2004, which is
hereby incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention is directed to the field of software
systems for processing real-time information.
BACKGROUND
[0003] Radiation therapy can be used to treat localized cancer. In
a typical application, a radiation delivery system has an ionizing
radiation device mounted to a movable gantry. The radiation
delivery system controls the motion of the radiation device to
direct an ionizing radiation beam to a specific point in space
commonly referred to as the "machine isocenter."
[0004] One aspect of radiation therapy is positioning a patient so
that the patient's tumor is located at the machine isocenter during
treatment. Conventional patient positioning systems use various
technologies to locate the tumor, including optically locating
visual markers applied to the patient's skin, or using X-ray
imaging to locate metal fiducials subcutaneously implanted in the
patient. Conventional patient positioning systems are typically
used only to align patients in preparation for the delivery of
radiation energy.
[0005] To ensure that radiation energy is delivered to a patient's
tumor as planned, though, it would be useful to provide patient
location information during the delivery of radiation energy. It
can be difficult to successfully apply conventional approaches to
patient tracking to provide patient location information during the
delivery of radiation, however.
[0006] Using conventional X-ray based tracking techniques, each
tracking measurement exposes the patient to an additional dose of
X-ray imaging radiation. Were the use of X-ray based tracking
expanded to operate throughout the course of radiation therapy, the
patient would be exposed to potentially harmful levels of X-ray
imaging radiation. Additionally, in some implementations, the
delivery of energy during radiation therapy can interrupt the
efficacy of X-ray based tracking techniques. For instance, the
presence of radiation therapy radiation may interfere with the
sensing of imaging radiation. As another example, the presence of
the X-ray imaging emitter and/or sensor may physically interrupt
the radiation treatment energy beam.
[0007] It can also be difficult to successfully apply conventional
optical tracking techniques during the delivery of radiation. Here
too, the presence of optical tracking sensors may interrupt the
radiation treatment energy beam. Conversely, radiation treatment
equipment may intervene between the patient and the optical
tracking sensors, blocking their view of the patient. Also, as
optical tracking techniques typically rely on 2-dimensional
tracking of the exterior surface of the patient's body, their
accuracy depends on the consistency of such factors as the shape of
the exterior surface of the patient's body, and the location of the
tumor relative to the locations of the visual markers. Because
these factors are inherently variable, positioning data obtained
using conventional optical tracking techniques can be
inaccurate.
[0008] In view of the foregoing, a patient tracking system that
provided useful patient tracking information during the delivery of
radiation energy, and that promptly acted on such information,
would have significant utility.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a data flow diagram showing a sample data flow
used by the facility.
[0010] FIG. 2 is a block diagram showing some of the components
typically incorporated in at least some of the computer systems and
other devices on which the facility executes.
[0011] FIG. 3 is a flow diagram showing steps typically performed
by the facility in the patient tracking component.
[0012] FIG. 4 is a flow diagram showing steps typically performed
by the caching component.
[0013] FIG. 5 is a display diagram showing a sample user interface
presented by a user interface component.
[0014] FIG. 6 is a data structure diagram showing sample contents
of the transcript stored by the patient tracking component and/or
the database component.
[0015] FIG. 7 is a side elevation view of a tracking system for use
in localizing and monitoring a target in accordance with an
embodiment of the present invention. Excitable markers are shown
implanted in or adjacent to a target in the patient.
[0016] FIG. 8 is a schematic elevation view of the patient on a
movable support table and of markers implanted in the patient.
[0017] FIG. 9 is a side view schematically illustrating a
localization system and a plurality of markers implanted in a
patient in accordance with an embodiment of the invention.
[0018] FIG. 10 is a flow diagram of an integrated radiation therapy
process that uses real time target tracking for radiation therapy
in accordance with an embodiment of the invention.
[0019] FIG. 11A is a representation of a CT image illustrating an
aspect of a system and method for real time tracking of targets in
radiation therapy and other medical applications.
[0020] FIG. 11B is a diagram schematically illustrating a reference
frame of a CT scanner.
[0021] FIG. 12 is a screenshot of a user interface for displaying
an objective output in accordance with an embodiment of the
invention.
[0022] FIG. 13 is an isometric view of a radiation session in
accordance with an embodiment of the invention.
[0023] FIG. 14A is an isometric view of a marker for use with a
localization system in accordance with an embodiment of the
invention.
[0024] FIG. 14B is a cross-sectional view of the marker of FIG. 14A
taken along line 14B-14B.
[0025] FIG. 14C is an illustration of a radiographic image of the
marker of FIGS. 14A-14B.
[0026] FIG. 15A is an isometric view of a marker for use with a
localization system in accordance with another embodiment of the
invention.
[0027] FIG. 15B is a cross-sectional view of the marker of FIG. 15A
taken along line 15B-15B.
[0028] FIG. 16A is an isometric view of a marker for use with a
localization system in accordance with another embodiment of the
invention.
[0029] FIG. 16B is a cross-sectional view of the marker of FIG. 16A
taken along line 16B-16B.
[0030] FIG. 17 is an isometric view of a marker for use with a
localization system in accordance with another embodiment of the
invention.
[0031] FIG. 18 is an isometric view of a marker for use with a
localization system in accordance with yet another embodiment of
the invention.
[0032] FIG. 19 is a schematic block diagram of a localization
system for use in tracking a target in accordance with an
embodiment of the invention.
[0033] FIG. 20 is a schematic view of an array of coplanar source
coils carrying electrical signals in a first combination of phases
to generate a first excitation field.
[0034] FIG. 21 is a schematic view of an array of coplanar source
coils carrying electrical signals in a second combination of phases
to generate a second excitation field.
[0035] FIG. 22 is a schematic view of an array of coplanar source
coils carrying electrical signals in a third combination of phases
to generate a third excitation field.
[0036] FIG. 23 is a schematic view of an array of coplanar source
coils illustrating a magnetic excitation field for energizing
markers in a first spatial orientation.
[0037] FIG. 24 is a schematic view of an array of coplanar source
coils illustrating a magnetic excitation field for energizing
markers in a second spatial orientation.
[0038] FIG. 25A is an exploded isometric view showing individual
components of a sensor assembly for use with a localization system
in accordance with an embodiment of the invention.
[0039] FIG. 25B is a top plan view of a sensing unit for use in the
sensor assembly of FIG. 25A.
[0040] FIG. 26 is a schematic diagram of a preamplifier for use
with the sensor assembly of FIG. 25A.
[0041] FIG. 27 is a graph of illustrative tumor motion ellipses
from experimental phantom based studies of the system.
[0042] FIG. 28 is a graph of root mean square (RMS) error from
experimental phantom based studies of the system.
[0043] FIG. 29 is an exemplary histogram of localization error from
experimental phantom based studies of the system.
[0044] FIG. 30 is graph of position error as a function of speed
from experimental phantom based studies of the system.
[0045] In the drawings, identical reference numbers identify
similar elements or components. The sizes and relative positions of
elements in the drawings are not necessarily drawn to scale. For
example, the shapes of various elements and angles are not drawn to
scale, and some of these elements are arbitrarily enlarged and
positioned to improve drawing legibility. Further, the particular
shapes of the elements as drawn, are not intended to convey any
information regarding the actual shape of the particular elements,
and have been solely selected for ease of recognition in the
drawings.
DETAILED DESCRIPTION
Introduction
[0046] A software facility that performs real-time or
near-real-time processing of patient tracking information during
radiation therapy ("the facility") is described. As one
illustrative example, some embodiments of the facility perform
processing for patient tracking information generated in real-time
or near-real-time by combining (1) information about the location
of subcutaneously-implanted markers--such as passive magnetic
transponders--relative to the sensor device used to locate the
markers--such as an electromagnetic excitation and sensing
array--with (2) information about the location of the sensor device
relative to a machine isocenter to which radiation energy is
delivered. One or more suitable, exemplary patient localization
systems are described in the following, each of which is hereby
incorporated by reference in its entirety: U.S. patent application
Ser. No. 10/334,700, entitled PANEL-TYPE SENSOR/SOURCE ARRAY
ASSEMBLY, filed Dec. 30, 2002; U.S. patent application Ser. No.
09/877,498, entitled GUIDED RADIATION THERAPY SYSTEM, filed Jun. 8,
2001; U.S. patent application Ser. No. 10/679,801, entitled METHOD
AND SYSTEM FOR MARKER LOCALIZATION, filed Oct. 6, 2003; U.S. patent
application Ser. No. 10/746,888, entitled IMPLANTABLE MARKER WITH
WIRELESS SIGNAL TRANSMITTAL, filed Dec. 24, 2003; and U.S. patent
application Ser. No. 10/749,478, entitled RECEIVER USED IN MARKER
LOCALIZATION SENSING SYSTEM, filed Dec. 31, 2003.
[0047] In some embodiments, the facility uses a publish and
subscribe scheme to promptly distribute patient tracking
information for one or more real-time or near-real-time uses. For
example, the facility may use the publish and subscribe scheme to
distribute patient tracking information to a user interface
component to display the patient's position for monitoring and/or
to a treatment control component to adapt the treatment process to
changes in the patient's position. In some embodiments, published
patient tracking information is cached for lower-frequency uses of
patient tracking information, and/or fixed-frequency uses of
patient tracking information, such as displaying.
[0048] In some embodiments, the facility uses a bulk transfer
scheme to less-frequently distribute patient tracking information,
such as at the end of a session. The bulk transfer scheme may be
used to distribute an entire session's patient tracking
information, for example for non-volatile storage or use in
planning a future treatment session.
[0049] By processing patient tracking information in some or all of
the ways discussed above, the facility enables a variety of
valuable uses of patient tracking information in connection with
radiation therapy.
Processing Patient Tracking Information
[0050] FIG. 1 is a data flow diagram showing a sample data flow
used by the facility. A patient tracking component 100 is
responsible for generating patient tracking records each indicating
the current location and/or orientation of a patient isocenter
relative to a reference point, such as relative to a machine
isocenter during radiation treatment. The patient tracking
component subscribes to objects of at least two types: marker
tracking record objects 111 published by a marker tracking
component 110, and sensor tracking record objects 121, published by
a sensor tracking component 120. The marker tracking record objects
each contain a marker tracking record indicating the location
and/or orientation of one or more markers implanted in the patient
relative to the location and/or orientation of a marker sensor.
Each sensor tracking record object contains a sensor tracking
record indicating a position and/or orientation of the marker
sensor device relative to the machine isocenter or other reference
point. Using information contained in the marker tracking records
and sensor tracking records that it receives, the patient tracking
component computes the location and/or orientation of a patient
isocenter--defined relative to the locations and/or orientation of
the implanted markers--relative to the machine isocenter.
[0051] In some embodiments, the patient tracking component computes
patient tracking records with no more than a maximum latency after
the time of the underlying measurements, such as a maximum latency
of 50 milliseconds, or a maximum latency of 200 milliseconds. In
some embodiments, the patient tracking component generates patient
tracking records at at least a minimum frequency, such as a minimum
frequency of 20 hertz. Additional detail about the generation of
patient tracking records is discussed in U.S. patent application
Ser. No. 11/166,801 entitled SYSTEMS AND METHODS FOR REAL TIME
TRACKING OF TARGETS IN RADIATION THERAPY AND OTHER MEDICAL
APPLICATIONS, filed Jun. 24, 2005 and incorporated by reference in
its entirety.
[0052] For each set of patient tracking information it computes,
the patient tracking component stores a patient tracking record in
a transcript 109 maintained by the patient tracking component, and
publishes a patient tracking record object 101 containing the
patient tracking record.
[0053] In some embodiments, the patient tracking component
truncates, or "prunes" the contents of the patient tracking records
included in the patient tracking record objects to reduce the
communication resources needed to publish patient tracking record
objects containing the pruned patient tracking records.
[0054] The patient tracking record objects published by the patient
tracking component are subscribed to by components seeking
real-time or near-real-time patient tracking information during the
course of a radiation treatment session. For example, a treatment
control component 130 may subscribe to the patient tracking record
objects, and use the enclosed patient tracking records to control a
variety of radiation treatment parameters. For example, in response
to the patient tracking information, the treatment control
component may alter the shape, direction, or intensity of the
radiation energy being used to treat the patient; alter the
location or orientation of the patient relative to the beam, such
as by automatically moving the patient (or a table supporting the
patient) or the beam; or switch the beam on or off, or pulse the
beam. Additional details regarding the treatment control
component's control of radiation treatment parameters are discussed
in the patent applications incorporated by reference above.
[0055] In some embodiments, a caching component 140 also subscribes
to the patient tracking record objects. The caching component 140
stores the patient tracking record contained in the most recently
published patient tracking record object in a cache 149.
Periodically, in some embodiments, one or more user interface
components 150 send the caching component a cached patient tracking
record request 151. (In some embodiments, however, some or all of
the user interface components directly subscribe to the patient
tracking record objects.) When the caching component receives a
cached patient tracking record request from one of the user
interface components, the caching component replies with a cached
patient tracking record 141--i.e., the patient tracking record
presently contained in the cache. As is discussed in additional
detail in U.S. patent application Ser. No. 60/590,699, entitled
USER INTERFACE FOR GUIDED RADIATION THERAPY, filed Jul. 23, 2004
and U.S. patent application Ser. No. ______ (patent counsel's
docket no. 341148029US1) entitled USER INTERFACE FOR GUIDED
RADIATION THERAPY, filed concurrently herewith, each of which is
hereby incorporated by reference in its entirety, the user
interfaces use the patient tracking records contained in the cached
patient tracking record response to present a visual or other user
interface reporting the patient tracking information, such as to
radiation treatment attendants, in a graph or other form.
[0056] When a patient treatment session is completed, the patient
tracking component sends a patient tracking transcript transmission
102, containing the transcript of the patient tracking records
generated during the session. The patient tracking transcript
transmission is sent to such recipients as a database 164 that
stores the transcript in a non-volatile manner, and a treatment
planning component 170 that uses the transcript to plan future
treatment sessions for the same patient. Such adaptive treatment
planning is discussed in additional detail in U.S. patent
application Ser. No. 60/590,503, filed Jul. 23, 2004, entitled
DYNAMIC/ADAPTIVE TREATMENT PLANNING FOR RADIATION THERAPY, and U.S.
patent application Ser. No. ______ (patent counsel's docket no.
341148031US1), entitled DYNAMIC/ADAPTIVE TREATMENT PLANNING FOR
RADIATION THERAPY, filed concurrently herewith, each of which is
hereby incorporated by reference in its entirety.
[0057] The components shown in FIG. 1 may be implemented and may
communicate in a variety of ways, including one or more discussed
in U.S. patent application Ser. No. 60/590,697, entitled MODULAR
SOFTWARE SYSTEM FOR GUIDED RADIATION THERAPY, filed on Jul. 23,
2004, and U.S. patent application Ser. No. ______ (patent counsel's
docket no. 341148028US1), entitled MODULAR SOFTWARE SYSTEM FOR
GUIDED RADIATION THERAPY, filed concurrently herewith, each of
which is hereby incorporated by reference in its entirety.
[0058] FIG. 2 is a block diagram showing some of the components
typically incorporated in at least some of the computer systems and
other devices on which the facility executes. These computer
systems and devices 200 may include one or more central processing
units ("CPUs") 201 for executing computer programs; a computer
memory 202 for storing programs and data-including data
structures--while they are being used; a persistent storage device
203, such as a hard drive, for persistently storing programs and
data; a computer-readable media drive 104, such as a CD-ROM drive,
for reading programs and data stored on a computer-readable medium;
and a network connection 205 for connecting the computer system to
other computer systems, such as via the Internet, to exchange
programs and/or data--including data structures. While computer
systems configured as described above are typically used to support
the operation of the facility, one of ordinary skill in the art
will appreciate that the facility may be implemented using devices
of various types and configurations, and having various
components.
[0059] FIG. 3 is a flow diagram showing steps typically performed
by the facility in the patient tracking component. In step 301, the
patient tracking component subscribes to the marker tracking record
object published by the marker tracking component. In step 302, the
patient tracking component subscribes to the sensor tracking record
object published by the sensor tracking component. In step 303, a
treatment session is conducted, during which the patient tracking
component uses marker and sensor tracking records contained in
published marker and sensor tracking record objects to generate
patient tracking records. The patient tracking component logs the
generated patient tracking records, and publishes patient tracking
record objects containing the generated patient tracking records.
In some embodiments, the published patient tracking record objects
contain pruned versions of the generated patient tracking records.
In step 304, at the conclusion of the patient treatment session,
the patient tracking component transmits a transcript of the
patient tracking records that were logged to one or more transcript
recipients. After step 304, these steps conclude.
[0060] FIG. 4 is a flow diagram showing steps typically performed
by the caching component. In step 401, the caching component
receives a published patient tracking record object from the
patient tracking component. In step 402, the caching component
replaces the patient tracking record in its cache with the patient
tracking record contained in the patient tracking record object
received in step 401. After step 402, the caching component
continues in step 401 to receive the next published patient
tracking record object.
[0061] Simultaneously, in step 411, the caching component receives
a request for the cached patient tracking record, such as a request
submitted by one of the user interface components. In step 412, the
caching component replies to the request received in step 411 with
the patient tracking record currently contained in the cache. After
step 412, the caching component continues in step 411 to receive
the next request.
[0062] FIG. 5 is a display diagram showing a sample user interface
display presented by a user interface component. The presented
display, in addition to other contents, contains numerical and
graphical indications of the patient positioning information. In
some embodiments, these display contents are updated at a regular
periodic rate, such as 10 hertz. In some embodiments, the rate at
which these display contents are updated is based upon a time scale
configurable by users. FIG. 5 shows this information for the
lateral displacement of the patient isocenter from the machine
isocenter (i.e., along the x axis) (numerical indication 511 and
time-distance graph 512); a longitudinal displacement component
(i.e., along the y axis) (numerical indication 521 and
time-distance graph 522); and vertical displacement (i.e., along
the z axis) (numerical indication 521 and time-distance graph 523).
Those skilled in the art will appreciate that a variety of other
user interface displays, containing less, more, or different
information (including patient tracking information) may be
presented by the facility. In addition, the facility may present
user interfaces in modes other than visual, such as audible user
interfaces.
[0063] FIG. 6 is a data structure diagram showing sample contents
of the transcript stored by the patient tracking component and/or
the database component. The transcript includes a start date and
time 601, an end date and time 602, an indication 603 of the number
of patient tracking records in the transcript, and an indication
604 of the number of marker tracking records contained in the
transcript (not shown). The transcript further includes a table 610
made up of rows, such as row 611-624, each corresponding to a
different time. Each row is divided into the following columns: an
x displacement column 631 containing the directed distance in the x
dimension from the machine isocenter to the patient isocenter, a y
displacement column 632, a z displacement column 633, a confidence
level column 634 indicating a level of confidence in the record, a
result code column 635 indicating a result code, a psi column 636
indicating a first angular component of the orientation of the
patient isocenter relative to the machine isocenter, a phi column
637 containing a second angular component of the orientation, a
theta column 638 containing a third angular component of the
orientation, a measurement date and time column 639 containing an
indication of the time at which the measurements were made, and a
delta time column 640 indicating the amount of time elapsed between
the start date and time and the measurement date and time.
[0064] In some embodiments, the data shown in FIG. 6 is stored in
forms other than those shown in FIG. 6. For example, Table 1 below
shows the data contained in row 617 shown in FIG. 6 expressed in an
XML format.
TABLE-US-00001 TABLE 1 <SessionTargetData>
<TargetPosition> <X>-0.43109733458214217</X>
<Y>-0.066685713198866473</Y>
<Z>-0.37997479402471651</Z> </TargetPosition>
<ConfidenceIndex>0</ConfidenceIndex>
<ResultCode>Okay</ResultCode>
<Psi>90.000002504478161</Psi> <Phi>0</Phi>
<Theta>0</Theta>
<MeasurementDateTime>2004-05-25T14:47:45.5468750-07:00</Measurem-
entDateTime> </SessionTargetData>
[0065] Those skilled in the art will appreciate that a variety of
other formats, including other tag-based markup languages, may be
used to store and communicate this information.
[0066] In some embodiments, information stored by the facility in
the transcript provides a basis for revisiting the treatment
session, such as by replaying the user interface display of the
session. In some embodiments, the contents of a transcript may be
used to perform various forms of retrospective analysis of the
session, such as identifying the smallest volume containing every
target position throughout the session; determining the percentage
of the session during which the target was within a prescribed
volume; determining a total dosage of radiation received at the
target; etc.
[0067] In some embodiments, the facility stores more detailed
tracking information than is shown in FIG. 6. For example, in some
embodiments, the facility stores, for some or all of the rows,
position and/or orientation information for one or more
transponders or other markers upon which the facility's
determination of target location and/or patient isocenter
displacement from treatment isocenter is derived. Where the
facility stores this more detailed information, the transcript may
be used to re-evaluate the treatment session, such as by using a
different approach to derive target location and displacement from
lower-level measures.
[0068] In some embodiments, the facility passes a transcript or
similar data structure to a record and verify system in order to
verify that radiation treatment was delivered in accordance with a
plan. In some embodiments, the facility itself performs this
verification function. For example, in some embodiments, the
facility uses the timestamps of the patient location records in the
data structure to correlate the patient tracking records with
time-indexed information about the status of various radiation
treatment parameters, such as those prescribed in the radiation
therapy session plan for the session. The facility then uses this
time-correlated information to verify that treatment was delivered
in accordance with the plan.
Techniques for Sensing Location
A. Overview
[0069] FIGS. 7-30 illustrate a system and several components for
locating, tracking and monitoring a target within a patient in real
time in accordance with embodiments of the present invention. The
system and components guide and control the radiation therapy to
more effectively treat the target. Several embodiments of the
systems described below with reference to FIGS. 7-30 can be used to
treat targets in the lung, prostate, head, neck, breast and other
parts of the body in accordance with aspects of the present
invention. Additionally, the markers and localization systems shown
in FIGS. 7-30 may also be used in surgical applications or other
medical applications. Like reference numbers refer to like
components and features throughout the various figures.
[0070] Several embodiments of the invention are directed towards
methods for tracking a target, i.e., measuring the position and/or
the rotation of a target in substantially real time, in a patient
in medical applications. One embodiment of such a method comprises
collecting position data of a marker that is substantially fixed
relative to the target. This embodiment further includes
determining the location of the marker in an external reference
frame (i.e., a reference frame outside the patient) and providing
an objective output in the external reference frame that is
responsive to the location of the marker. The objective output is
repeatedly provided at a frequency/periodicity that adequately
tracks the location of the target in real time within a clinically
acceptable tracking error range. As such, the method for tracking
the target enables accurate tracking of the target during
diagnostic, planning, treatment or other types of medical
procedures. In many specific applications, the objective output is
provided within a suitably short latency after collecting the
position data and at a sufficiently high frequency to use the data
for such medical procedures.
[0071] Another specific embodiment is a method for treating a
target in a patient with an ionizing radiation beam that includes
collecting position information of a marker implanted within a
patient at a site relative to the target at a time t.sub.n, and
providing an objective output indicative of the location of the
target based on the position information collected at time t.sub.n.
The objective output is provided to a memory device, user
interface, and/or radiation delivery machine within 2 seconds or
less of the time t.sub.n when the position information was
collected. This embodiment of the method can further include
providing the objective output at a periodicity of 2 seconds or
less during at least a portion of a treatment procedure. For
example, the method can further include generating a beam of
ionizing radiation and directing the beam to a machine isocenter,
and continuously repeating the collecting procedure and the
providing procedure every 10-200 ms while irradiating the patient
with the ionizing radiation beam.
[0072] Another embodiment of a method for tracking a target in a
patient includes obtaining position information of a marker
situated within the patient at a site relative to the target, and
determining a location of the marker in an external reference frame
based on the position information. This embodiment further includes
providing an objective output indicative of the location of the
target to a user interface at (a) a sufficiently high frequency so
that pauses in representations of the target location at the user
interface are not readily discernable by a human, and (b) a
sufficiently low latency to be at least substantially
contemporaneous with obtaining the position information of the
marker.
[0073] Another embodiment of the invention is directed toward a
method of treating a target of a patient with an ionizing radiation
beam by generating a beam of ionizing radiation and directing the
beam relative to the target. This method further includes
collecting position information of a marker implanted within the
patient at a site relative to the target while directing the beam
toward the beam isocenter. Additionally, this method includes
providing an objective output indicative of a location of the
target relative to the beam isocenter based on the collected
position information. This method can further include correlating
the objective output with a parameter of the beam, and controlling
the beam based upon the objective output. For example, the beam can
be gated to only irradiate the patient when the target is within a
desired irradiation zone. Additionally, the patient can be moved
automatically and/or the beam can be shaped automatically according
to the objective output to provide dynamic control in real time
that maintains the target at a desired position relative to the
beam isocenter while irradiating the patient.
[0074] Various embodiments of the invention are described in this
section to provide specific details for a thorough understanding
and enabling description of these embodiments. A person skilled in
the art, however, will understand that the invention may be
practiced without several of these details, or that additional
details can be added to the invention. Where the context permits,
singular or plural terms may also include the plural or singular
term, respectively. Moreover, unless the word "or" is expressly
limited to mean only a single item exclusive from the other items
in reference to a list of at least two items, then the use of "or"
in such a list is to be interpreted as including (a) any single
item in the list, (b) all of the items in the list, or (c) any
combination of items in the list. Additionally, the term
"comprising" is used throughout to mean including at least the
recited feature(s) such that any greater number of the same feature
and/or types of other features or components are not precluded.
B. Radiation Therapy Systems with Real Time Tracking Systems
[0075] FIGS. 7 and 8 illustrate various aspects of a radiation
therapy system 1 for applying guided radiation therapy to a target
2 (e.g., a tumor) within a lung 4, prostate, breast, head, neck or
other part of a patient 6. The radiation therapy system 1 has a
localization system 10 and a radiation delivery device 20. The
localization system 10 is a tracking unit that locates and tracks
the actual position of the target 2 in real time during treatment
planning, patient setup, and/or while applying ionizing radiation
to the target from the radiation delivery device. Thus, although
the target 2 may move within the patient because of breathing,
organ filling/emptying, cardiac functions or other internal
movement as described above, the localization system 10 accurately
tracks the motion of the target relative to the external reference
frame of the radiation delivery device or other external reference
frame outside of the patient to accurately deliver radiation within
a small margin around the target. The localization system 10 can
also monitor the configuration and trajectory of the marker to
provide an early indicator of a change in the tumor without using
ionizing radiation. Moreover, the localization system 10
continuously tracks the target and provides objective data (e.g.,
three-dimensional coordinates in an absolute reference frame) to a
memory device, user interface, linear accelerator, and/or other
device. The system 1 is described below in the context of guided
radiation therapy for treating a tumor or other target in the lung
of the patient, but the system can be used for tracking and
monitoring the prostate gland or other targets within the patient
for other therapeutic and/or diagnostic purposes.
[0076] The radiation delivery source of the illustrated embodiment
is an ionizing radiation device 20 (i.e., a linear accelerator).
Suitable linear accelerators are manufactured by Varian Medical
Systems, Inc. of Palo Alto, Calif.; Siemens Medical Systems, Inc.
of Iselin, N.J.; Elekta Instruments, Inc. of Iselin, N.J.; or
Mitsubishi Denki Kabushik Kaisha of Japan. Such linear accelerators
can deliver conventional single or multi-field radiation therapy,
3D conformal radiation therapy (3D CRT), intensity modulated
radiation therapy (IMRT), stereotactic radiotherapy, and tomo
therapy. The radiation delivery source 20 can deliver a gated,
contoured or shaped beam 21 of ionizing radiation from a movable
gantry 22 to an area or volume at a known location in an external,
absolute reference frame relative to the radiation delivery source
20. The point or volume to which the ionizing radiation beam 21 is
directed is referred to as the machine isocenter.
[0077] The tracking system includes the localization system 10 and
one or more markers 40. The localization system 10 determines the
actual location of the markers 40 in a three-dimensional reference
frame, and the markers 40 are typically implanted within the
patient 6. In the embodiment illustrated in FIGS. 7 and 8, more
specifically, three markers identified individually as markers
40a-c are implanted in or near the lung 4 of the patient 6 at
locations in or near the target 2. In other applications, a single
marker, two markers, or more than three markers can be used
depending upon the particular application. Two markers, for
example, are desirable because the location of the target can be
determined accurately, and also because any relative displacement
between the two markers over time can be used to monitor marker
migration in the patient. The markers 40 are desirably placed
relative to the target 2 such that the markers 40 are at least
substantially fixed relative to the target 2 (e.g., the markers
move directly with the target or at least in direct proportion to
the movement of the target). The relative positions between the
markers 40 and the relative positions between a target isocenter T
of the target 2 and the markers 40 can be determined with respect
to an external reference frame defined by a CT scanner or other
type of imaging system during a treatment planning stage before the
patient is placed on the table. In the particular embodiment of the
system 1 illustrated in FIGS. 7 and 8, the localization system 10
tracks the three-dimensional coordinates of the markers 40 in real
time relative to an absolute external reference frame during the
patient setup process and while irradiating the patient to mitigate
collateral effects on adjacent healthy tissue and to ensure that
the desired dosage is applied to the target.
C. General Aspects of Markers and Localization Systems
[0078] FIG. 9 is a schematic view illustrating the operation of an
embodiment of the localization system 10 and markers 40a-c for
treating a tumor or other target in the patient. The localization
system 10 and the markers 40a-c are used to determine the location
of the target 2 (FIGS. 7 and 8) before, during and after radiation
sessions. More specifically, the localization system 10 determines
the locations of the markers 40a-c and provides objective target
position data to a memory, user interface, linear accelerator
and/or other device in real time during setup, treatment,
deployment, simulation, surgery, and/or other medical procedures.
In one embodiment of the localization system, real time means that
indicia of objective coordinates are provided to a user interface
at (a) a sufficiently high refresh rate (i.e., frequency) such that
pauses in the data are not humanly discernable and (b) a
sufficiently low latency to be at least substantially
contemporaneous with the measurement of the location signal. In
other embodiments, real time is defined by higher frequency ranges
and lower latency ranges for providing the objective data to a
radiation delivery device. In some embodiments, real time is
defined as providing objective data periodically responsive to the
location of the markers, with a sufficiently short period that
tracking errors are within clinically acceptable limits.
1. Localization Systems
[0079] The localization system 10 includes an excitation source 60
(e.g., a pulsed magnetic field generator), a sensor assembly 70,
and a controller 80 coupled to both the excitation source 60 and
the sensor assembly 70. The excitation source 60 generates an
excitation energy to energize at least one of the markers 40a-c in
the patient 6 (FIG. 7). The embodiment of the excitation source 60
shown in FIG. 9 produces a pulsed magnetic field at different
frequencies. For example, the excitation source 60 can frequency
multiplex the magnetic field at a first frequency E.sub.1 to
energize the first marker 40a, a second frequency E.sub.2 to
energize the second marker 40b, and a third frequency E.sub.3 to
energize the third marker 40c. In response to the excitation
energy, the markers 40a-c generate location signals L.sub.1-3 at
unique response frequencies. More specifically, the first marker
40a generates a first location signal L.sub.1 at a first frequency
in response to the excitation energy at the first frequency
E.sub.1, the second marker 40b generates a second location signal
L.sub.2 at a second frequency in response to the excitation energy
at the second frequency E.sub.2, and the third marker 40c generates
a third location signal L.sub.3 at a third frequency in response to
the excitation energy at the third frequency E.sub.3. In an
alternative embodiment with two markers, the excitation source
generates the magnetic field at frequencies E.sub.1 and E.sub.2,
and the markets 40a-b generate location signals L.sub.1 and
L.sub.2, respectively.
[0080] The sensor assembly 70 can include a plurality of coils to
sense the location signals L.sub.1-3 from the markers 40a-c. The
sensor assembly 70 can be a flat panel having a plurality of coils
that are at least substantially coplanar relative to each other. In
other embodiments, the sensor assembly 70 may be a non-planar array
of coils.
[0081] The controller 80 includes hardware, software or other
computer-operable media containing instructions that operate the
excitation source 60 to multiplex the excitation energy at the
different frequencies E.sub.1-3. For example, the controller 80
causes the excitation source 60 to generate the excitation energy
at the first frequency E.sub.1 for a first excitation period, and
then the controller 80 causes the excitation source 60 to terminate
the excitation energy at the first frequency E.sub.1 for a first
sensing phase during which the sensor assembly 70 senses the first
location signal L.sub.1 from the first marker 40a without the
presence of the excitation energy at the first frequency E.sub.1.
The controller 80 then causes the excitation source 60 to: (a)
generate the second excitation energy at the second frequency
E.sub.2 for a second excitation period; and (b) terminate the
excitation energy at the second frequency E.sub.2 for a second
sensing phase during which the sensor assembly 70 senses the second
location signal L.sub.2 from the second marker 40b without the
presence of the second excitation energy at the second frequency
E.sub.2. The controller 80 then repeats this operation with the
third excitation energy at the third frequency E.sub.3 such that
the third marker 40c transmits the third location signal L.sub.3 to
the sensor assembly 70 during a third sensing phase. As such, the
excitation source 60 wirelessly transmits the excitation energy in
the form of pulsed magnetic fields at the resonant frequencies of
the markers 40a-c during excitation periods, and the markers 40a-c
wirelessly transmit the location signals L.sub.1-3 to the sensor
assembly 70 during sensing phases. It will be appreciated that the
excitation and sensing phases can be repeated to permit averaging
of the sensed signals to reduce noise.
[0082] The computer-operable media in the controller 80, or in a
separate signal processor, or other computer also includes
instructions to determine the absolute positions of each of the
markers 40a-c in a three-dimensional reference frame. Based on
signals provided by the sensor assembly 70 that correspond to the
magnitude of each of the location signals L.sub.1-3, the controller
80 and/or a separate signal processor calculates the absolute
coordinates of each of the markers 40a-c in the three-dimensional
reference frame. The absolute coordinates of the markers 40a-c are
objective data that can be used to calculate the coordinates of the
target in the reference frame. When multiple markers are used, the
rotation of the target can also be calculated.
2. Real Time Tracking
[0083] The localization system 10 and at least one of a marker 40
enables real time tracking of the target 2 relative to the machine
isocenter or another external reference frame outside of the
patient during treatment planning, set up, radiation sessions, and
at other times of the radiation therapy process. In many
embodiments, real time tracking means collecting position data of
the markers, determining the locations of the markers in an
external reference frame, and providing an objective output in the
external reference frame that is responsive to the location of the
markers. The objective output is provided at a frequency that
adequately tracks the target in real time and/or a latency that is
at least substantially contemporaneous with collecting the position
data (e.g., within a generally concurrent period of time).
[0084] For example, several embodiments of real time tracking are
defined as determining the locations of the markers and calculating
the location of the target relative to the machine isocenter at (a)
a sufficiently high frequency so that pauses in representations of
the target location at a user interface do not interrupt the
procedure or are readily discernable by a human, and (b) a
sufficiently low latency to be at least substantially
contemporaneous with the measurement of the location signals from
the markers. Alternatively, real time means that the location
system 10 calculates the absolute position of each individual
marker 40 and/or the location of the target at a periodicity of 1
ms to 5 seconds, or in many applications at a periodicity of
approximately 10-100 ms, or in some specific applications at a
periodicity of approximately 20-50 ms. In applications for user
interfaces, for example, the periodicity can be 12.5 ms (i.e., a
frequency of 80 Hz), 16.667 ms (60 Hz), 20 ms (50 Hz), and/or 50 ms
(20 Hz).
[0085] Alternatively, real time tracking can further mean that the
location system 10 provides the absolute locations of the markers
40 and/or the target 2 to a memory device, user interface, linear
accelerator or other device within a latency of 10 ms to 5 seconds
from the time the localization signals were transmitted from the
markers 40. In more specific applications, the location system
generally provides the locations of the markers 40 and/or target 2
within a latency of about 20-50 ms. The location system 10
accordingly provides real time tracking to monitor the position of
the markers 40 and/or the target 2 with respect to an external
reference frame in a manner that is expected to enhance the
efficacy of radiation therapy because higher radiation doses can be
applied to the target and collateral effects to healthy tissue can
be mitigated.
[0086] Alternatively, real-time tracking can further be defined by
the tracking error. Measurements of the position of a moving target
are subject to motion-induced error, generally referred to as a
tracking error. According to aspects of the present invention, the
localization system 10 and at least one marker 4 enable real time
tracking of the target 2 relative to the machine isocenter or
another external reference frame with a tracking error that is
within clinically meaningful limits.
[0087] Tracking errors are due to two limitations exhibited by any
practical measurement system, specifically (a) latency between the
time the target position is sensed and the time the position
measurement is made available, and (b) sampling delay due to the
periodicity of measurements. For example, if a target is moving at
5 cm/s and a measurement system has a latency of 200 ms, then
position measurements will be in error by 1 cm. The error in this
example is due to latency alone, independent of any other
measurement errors, and is simply due to the fact that the target
has moved between the time its position is sensed and the time the
position measurement is made available for use. If this exemplary
measurement system further has a sampling periodicity of 200 ms
(i.e., a sampling frequency of 5 Hz), then the peak tracking error
increases to 2 cm, with an average tracking error of 1.5 cm.
[0088] For a real time tracking system to be useful in medical
applications, it is desirable to keep the tracking error within
clinically meaningful limits. For example, in a system for tracking
motion of a tumor in a lung for radiation therapy, it may be
desirable to keep the tracking error within 5 mm. Acceptable
tracking errors may be smaller when tracking other organs for
radiation therapy. In accordance with aspects of the present
invention, real time tracking refers to measurement of target
position and/or rotation with tracking errors that are within
clinically meaningful limits.
[0089] In some embodiments, the system temporally filters the
measurements of the marker locations, or the calculated location of
the target, in order to reduce the effects of additive noise or
other measurement errors. Such filtering has the effect of
increasing the latency, hence the tracking error, of the system.
Conversely, reducing the filtering has the effect of reducing the
tracking error, at the price of increasing the effects of noise. In
some embodiments, the system periodically measures the vector
velocity (or a similar state variable) of the markers or the
target, in addition to their locations. Such an approach can
improve the accuracy of subsequent location measurements. In this
case, filtering can be applied to measurements of vector velocity
as well. Techniques to implement temporal filtering are well known
to those skilled in the art, and include recursive and
non-recursive digital filters, and Kalman and other non-linear
filters. References herein to location data, or digital location
indications, or the like, include those data which have been
filtered, or derived from filtered measurements.
[0090] The system described herein uses one or more markers to
serve as registration points to characterize target location,
rotation, and motion. In accordance with aspects of the invention,
the markers have a substantially fixed relationship with the
target. If the markers did not have a substantially fixed
relationship with the target another type of tracking error would
be incurred. This generally requires the markers to be fixed or
implanted sufficiently close to the target in order that tracking
errors be within clinically meaningful limits, thus, the markers
may be placed in tissue or bone that exhibits representative motion
of the target. For example, with respect to the prostate, tissue
that is representative of the target's motion would include tissue
in close proximity or adjacent to the prostate. Tissue adjacent to
a target involving the prostate may include the prostate gland, the
tumor itself, or tissue within a specified radial distance from the
target. With respect to the prostate, tracking tissue that is a 5
cm radial distance from the target would provide representative
motion that is clinically useful to the motion of the target. In
accordance with alternative target tracking locations, the radial
distance may be greater or lesser.
[0091] According to aspects of the present invention, the marker
motion is a surrogate for the motion of the target. Accordingly,
the marker is placed such that it moves in direct correlation to
the target being tracked. Depending on the target being tracked,
the direct correlation relationship between the target and the
marker will vary. For example, in long bones, the marker may be
place anywhere along the bone to provide motion that directly
correlate to target motion in the bone. With respect to soft tissue
that moves substantially in response to the bony anatomy, for
example, the head and neck, the marker may be placed in a bite
block to provide surrogate motion in direct correlation with target
motion. With respect to soft tissue and as discussed in detail
above, the target may be placed in adjacent soft tissue to provide
a surrogate having direct correlation to target motion.
[0092] FIG. 10 is a flow diagram illustrating several aspects and
uses of real time tracking to monitor the location and the status
of the target. In this embodiment, an integrated method 90 for
radiation therapy includes a radiation planning procedure 91 that
determines the plan for applying the radiation to the patient over
a number of radiation fractions. The radiation planning procedure
91 typically includes an imaging stage in which images of a tumor
or other types of targets are obtained using X-rays, CT, MRI, or
ultrasound imaging. The images are analyzed by a person to measure
the relative distances between the markers and the relative
position between the target and the markers. FIG. 11A, for example,
is a representation of a CT image showing a cross-section of the
patient 6, the target 2, and a marker 40. Referring to FIG. 11B,
the coordinates (x.sub.0, y.sub.0, z.sub.0) of the marker 40 in a
reference frame R.sub.CT of the CT scanner can be determined by an
operator. The coordinates of the tumor can be determined in a
similar manner to ascertain the offset between the marker and the
target.
[0093] The radiation planning procedure 91 can also include
tracking the targets using the localization system 10 (FIG. 9) in
an observation area separate from the imaging equipment. The
markers 40 (FIG. 9) can be tracked to identify changes in the
configuration (e.g., size/shape) of the target over time and to
determine the trajectory of the target caused by movement of the
target within the patient (e.g., simulation). For many treatment
plans, the computer does not need to provide objective output data
of the marker or target locations to a user in real time, but
rather the data can be recorded in real time. Based on the images
obtained during the imaging stage and the additional data obtained
by tracking the markers using the localization system 10 in a
simulation procedure, a treatment plan is developed for applying
the radiation to the target.
[0094] The localization system 10 and the markers 40 enable an
automated patient setup process for delivering the radiation. After
developing a treatment plan, the method 90 includes a setup
procedure 92 in which the patient is positioned on a movable
support table so that the target and markers are generally adjacent
to the sensor assembly. As described above, the excitation source
is activated to energize the markers, and the sensors measure the
strength of the signals from the markers. The computer controller
then (a) calculates objective values of the locations of the
markers and the target relative to the machine isocenter, and (b)
determines an objective offset value between the position of the
target and the machine isocenter. Referring to FIG. 12, for
example, the objective offset values can be provided to a user
interface that displays the vertical, lateral and longitudinal
offsets of the target relative to the machine isocenter. A user
interface may, additionally or instead, display target
rotation.
[0095] One aspect of several embodiments of the localization system
10 is that the objective values are provided to the user interface
or other device by processing the position data from the field
sensor 70 in the controller 80 or other computer without human
interpretation of the data received by the field sensor 70. If the
offset value is outside of an acceptable range, the computer
automatically activates the control system of the support table to
move the tabletop relative to the machine isocenter until the
target isocenter is coincident with the machine isocenter. The
computer controller generally provides the objective output data of
the offset to the table control system in real time as defined
above. For example, because the output is provided to the radiation
delivery device, it can be at a high rate (1-20 ms) and a low
latency (10-20 ms). If the output data is provided to a user
interface in addition to or in lieu of the table controller, it can
be at a relatively lower rate (20-50 ms) and higher latency (50-200
ms).
[0096] In one embodiment, the computer controller also determines
the position and orientation of the markers relative to the
position and orientation of simulated markers. The locations of the
simulated markers are selected so that the target will be at the
machine isocenter when the real markers are at the selected
locations for the simulated markers. If the markers are not
properly aligned and oriented with the simulated markers, the
support table is adjusted as needed for proper marker alignment.
This marker alignment properly positions the target along six
dimensions, namely X, Y, Z, pitch, yaw, and roll. Accordingly, the
patient is automatically positioned in the correct position and
rotation relative to the machine isocenter for precise delivery of
radiation therapy to the target.
[0097] Referring back to FIG. 10, the method 90 further includes a
radiation session 93. FIG. 13 shows a further aspect of an
automated process in which the localization system 10 tracks the
target during the radiation session 93 and controls the radiation
delivery device 20 according to the offset between target and the
machine isocenter. For example, if the position of the target is
outside of a permitted degree or range of displacement from the
machine isocenter, the localization system 10 sends a signal to
interrupt the delivery of the radiation or prevent initial
activation of the beam. In another embodiment, the localization
system 10 sends signals to automatically reposition a tabletop 27
and the patient 6 (as a unit) so that the target isocenter remains
within a desired range of the machine isocenter during the
radiation session 93 even if the target moves. In still another
embodiment, the localization system 10 sends signals to activate
the radiation only when the target is within a desired range of the
machine isocenter (e.g., gated therapy). In the case of treating a
target in the lung, one embodiment of gated therapy includes
tracking the target during inspiration/expiration, having the
patient hold his/her breath at the end of an inspiration/expiration
cycle, and activating the beam 21 when the computer 80 determines
that the objective offset value between the target and the machine
isocenter is within a desired range. Accordingly, the localization
system enables dynamic adjustment of the table 27 and/or the beam
21 in real time while irradiating the patient. This is expected to
ensure that the radiation is accurately delivered to the target
without requiring a large margin around the target.
[0098] The localization system provides the objective data of the
offset and/or rotation to the linear accelerator and/or the patient
support table in real time as defined above. For example, as
explained above with respect to automatically positioning the
patent support table during the setup procedure 92, the
localization system generally provides the objective output to the
radiation delivery device at least substantially contemporaneously
with obtaining the position data of the markers and/or at a
sufficient frequency to track the target in real time. The
objective output, for example, can be provided at a short
periodicity (1-20 ms) and a low latency (10-20 ms) such that
signals for controlling the beam 21 can be sent to the radiation
delivery device 20 in the same time periods during a radiation
session. In another example of real time tracking, the objective
output is provided a plurality of times during an "on-beam" period
(e.g., 2, 5, 10 or more times while the beam is on). In the case of
terminating or activating the radiation beam, or adjusting the
leafs of a beam collimator, it is generally desirable to maximize
the refresh rate and minimize the latency. In some embodiments,
therefore, the localization system may provide the objective output
data of the target location and/or the marker locations at a
periodicity of 10 ms or less and a latency of 10 ms or less.
[0099] The method 90 further includes a verification procedure 94
in which the real time objective output data from the radiation
session 93 is compared to the status of the parameters of the
radiation beam. For example, the target locations can be correlated
with the beam intensity, beam position, and collimator
configuration at corresponding time intervals during the radiation
session 93. This correlation can be used to determine the dose of
radiation delivered to discrete regions in and around the target.
This information can also be used to determine the effects of
radiation on certain areas of the target by noting changes in the
target configuration or the target trajectory.
[0100] The method 90 can further include a first decision (Block
95) in which the data from the verification procedure 94 is
analyzed to determine whether the treatment is complete. If the
treatment is not complete, the method 90 further includes a second
decision (Block 96) in which the results of the verification
procedure are analyzed to determine whether the treatment plan
should be revised to compensate for changes in the target. If
revisions are necessary, the method can proceed with repeating the
planning procedure 91. On the other hand, if the treatment plan is
providing adequate results, the method 90 can proceed by repeating
the setup procedure 92, radiation session 93, and verification
procedure 94 in a subsequent fraction of the radiation therapy.
[0101] The localization system 10 provides several features, either
individually or in combination with each other, that enhance the
ability to accurately deliver high doses of radiation to targets
within tight margins. For example, many embodiments of the
localization system use leadless markers that are implanted in the
patient so that they are substantially fixed with respect to the
target. The markers accordingly move either directly with the
target or in a relationship proportional to the movement of the
target. As a result, internal movement of the target caused by
respiration, organ filling, cardiac functions, or other factors can
be identified and accurately tracked before, during and after
medical procedures. Moreover, many aspects of the localization
system 10 use a non-ionizing energy to track the leadless markers
in an external, absolute reference frame in a manner that provides
objective output. In general, the objective output is determined in
a computer system without having a human interpret data (e.g.,
images) while the localization system 10 tracks the target and
provides the objective output. This significantly reduces the
latency between the time when the position of the marker is sensed
and the objective output is provided to a device or a user. For
example, this enables an objective output responsive to the
location of the target to be provided at least substantially
contemporaneously with collecting the position data of the marker.
The system also effectively eliminates inter-user variability
associated with subjective interpretation of data (e.g.,
images).
D. Specific Embodiments of Markers and Localization Systems
[0102] The following specific embodiments of markers, excitation
sources, sensors and controllers provide additional details to
implement the systems and processes described above with reference
to FIGS. 7-13. The present inventors overcame many challenges to
develop markers and localization systems that accurately determine
the location of a marker which (a) produces a wirelessly
transmitted location signal in response to a wirelessly transmitted
excitation energy, and (b) has a cross-section small enough to be
implanted in the lung, prostate, or other part of a patient.
Systems with these characteristics have several practical
advantages, including (a) not requiring ionization radiation, (b)
not requiring line-of-sight between the markers and sensors, and
(c) effecting an objective measurement of a target's location
and/or rotation. The following specific embodiments are described
in sufficient detail to enable a person skilled in the art to make
and use such a localization system for radiation therapy involving
a tumor in the patient, but the invention is not limited to the
following embodiments of markers, excitation sources, sensor
assemblies and/or controllers.
1. Markers
[0103] FIG. 14A is an isometric view of a marker 1400 for use with
the localization system 10 (FIGS. 7-13). The embodiment of the
marker 1400 shown in FIG. 14A includes a casing 1410 and a magnetic
transponder 1420 (e.g., a resonating circuit) in the casing 1410.
The casing 1410 is a barrier configured to be implanted in the
patient, or encased within the body of an instrument. The casing
1410 can alternatively be configured to be adhered externally to
the skin of the patient. The casing 1410 can be a generally
cylindrical capsule that is sized to fit within the bore of a small
introducer, such as bronchoscope or percutaneous trans-thoracic
implanter, but the casing 1410 can have other configurations and be
larger or smaller. The casing 1410, for example, can have barbs or
other features to anchor the casing 1410 in soft tissue or an
adhesive for attaching the casing 1410 externally to the skin of a
patient. Suitable anchoring mechanisms for securing the marker 1400
to a patient are disclosed in International Publication No. WO
02/39917 A1, which designates the United States and is incorporated
herein by reference. In one embodiment, the casing 1410 includes
(a) a capsule or shell 1412 having a closed end 1414 and an open
end 1416, and (b) a sealant 1418 in the open end 1416 of the shell
1412. The casing 1410 and the sealant 1418 can be made from
plastics, ceramics, glass or other suitable biocompatible
materials.
[0104] The magnetic transponder 1420 can include a resonating
circuit that wirelessly transmits a location signal in response to
a wirelessly transmitted excitation field as described above. In
this embodiment, the magnetic transponder 1420 comprises a coil
1422 defined by a plurality of windings of a conductor 1424. Many
embodiments of the magnetic transponder 1420 also include a
capacitor 1426 coupled to the coil 1422. The coil 1422 resonates at
a selected resonant frequency. The coil 1422 can resonate at a
resonant frequency solely using the parasitic capacitance of the
windings without having a capacitor, or the resonant frequency can
be produced using the combination of the coil 1422 and the
capacitor 1426. The coil 1422 accordingly generates an alternating
magnetic field at the selected resonant frequency in response to
the excitation energy either by itself or in combination with the
capacitor 1426. The conductor 1424 of the illustrated embodiment
can be hot air or alcohol bonded wire having a gauge of
approximately 45-52. The coil 1422 can have 800-1000 turns, and the
windings are preferably wound in a tightly layered coil. The
magnetic transponder 1420 can further include a core 1428 composed
of a material having a suitable magnetic permeability. For example,
the core 1428 can be a ferromagnetic element composed of ferrite or
another material. The magnetic transponder 1420 can be secured to
the casing 1410 by an adhesive 1429.
[0105] The marker 1400 also includes an imaging element that
enhances the radiographic image of the marker to make the marker
more discernible in radiographic images. The imaging element also
has a radiographic profile in a radiographic image such that the
marker has a radiographic centroid at least approximately
coincident with the magnetic centroid of the magnetic transponder
1420. As explained in more detail below, the radiographic and
magnetic centroids do not need to be exactly coincident with each
other, but rather can be within an acceptable range.
[0106] FIG. 14B is a cross-sectional view of the marker 1400 along
line 14B-14B of FIG. 14A that illustrates an imaging element 1430
in accordance with an embodiment of the invention. The imaging
element 1430 illustrated in FIGS. 14A-B includes a first contrast
element 1432 and second contrast element 1434. The first and second
contrast elements 1432 and 1434 are generally configured with
respect to the magnetic transponder 1420 so that the marker 1400
has a radiographic centroid R.sub.c that is at least substantially
coincident with the magnetic centroid M.sub.c of the magnetic
transponder 1420. For example, when the imaging element 1430
includes two contrast elements, the contrast elements can be
arranged symmetrically with respect to the magnetic transponder
1420 and/or each other. The contrast elements can also be
radiographically distinct from the magnetic transponder 1420. In
such an embodiment, the symmetrical arrangement of distinct
contrast elements enhances the ability to accurately determine the
radiographic centroid of the marker 1400 in a radiographic
image.
[0107] The first and second contrast elements 1432 and 1434
illustrated in FIGS. 14A-B are continuous rings positioned at
opposing ends of the core 1428. The first contrast element 1432 can
be at or around a first end 1436a of the core 1428, and the second
contrast element 1434 can be at or around a second end 1436b of the
core 1428. The continuous rings shown in FIGS. 14A-B have
substantially the same diameter and thickness. The first and second
contrast elements 1432 and 1434, however, can have other
configurations and/or be in other locations relative to the core
1428 in other embodiments. For example, the first and second
contrast elements 1432 and 1434 can be rings with different
diameters and/or thicknesses.
[0108] The radiographic centroid of the image produced by the
imaging element 1430 does not need to be absolutely coincident with
the magnetic centroid M.sub.c, but rather the radiographic centroid
and the magnetic centroid should be within an acceptable range. For
example, the radiographic centroid R.sub.c can be considered to be
at least approximately coincident with the magnetic centroid
M.sub.c when the offset between the centroids is less than
approximately 5 mm. In more stringent applications, the magnetic
centroid M.sub.c and the radiographic centroid R.sub.c are
considered to be at least substantially coincident with each other
when the offset between the centroids is 2 mm, or less than 1 mm.
In other applications, the magnetic centroid M.sub.c is at least
approximately coincident with the radiographic centroid R.sub.c
when the centroids are spaced apart by a distance not greater than
half the length of the magnetic transponder 1420 and/or the marker
1400.
[0109] The imaging element 1430 can be made from a material and
configured appropriately to absorb a high fraction of incident
photons of a radiation beam used for producing the radiographic
image. For example, when the imaging radiation has high
acceleration voltages in the megavoltage range, the imaging element
1430 is made from, at least in part, high density materials with
sufficient thickness and cross-sectional area to absorb enough of
the photon fluence incident on the imaging element to be visible in
the resulting radiograph. Many high energy beams used for therapy
have acceleration voltages of 6 MV-25 MV, and these beams are often
used to produce radiographic images in the 5 MV-10 MV range, or
more specifically in the 6 MV-8 MV range. As such, the imaging
element 1430 can be made from a material that is sufficiently
absorbent of incident photon fluence to be visible in an image
produced using a beam with an acceleration voltage of 5 MV-10 MV,
or more specifically an acceleration voltage of 6 MV-8 MV.
[0110] Several specific embodiments of imaging elements 1430 can be
made from gold, tungsten, platinum and/or other high density
metals. In these embodiments the imaging element 1430 can be
composed of materials having a density of 19.25 g/cm3 (density of
tungsten) and/or a density of approximately 21.4 g/cm3 (density of
platinum). Many embodiments of the imaging element 1430 accordingly
have a density not less than 19 g/cm3. In other embodiments,
however, the material(s) of the imaging element 1430 can have a
substantially lower density. For example, imaging elements with
lower density materials are suitable for applications that use
lower energy radiation to produce radiographic images. Moreover,
the first and second contrast elements 1432 and 1434 can be
composed of different materials such that the first contrast
element 1432 can be made from a first material and the second
contrast element 1434 can be made from a second material.
[0111] Referring to FIG. 14B, the marker 1400 can further include a
module 1440 at an opposite end of the core 1428 from the capacitor
1426. In the embodiment of the marker 1400 shown in FIG. 14B, the
module 1440 is configured to be symmetrical with respect to the
capacitor 1426 to enhance the symmetry of the radiographic image.
As with the first and second contrast elements 1432 and 1434, the
module 1440 and the capacitor 1426 are arranged such that the
magnetic centroid of the marker is at least approximately
coincident with the radiographic centroid of the marker 1400. The
module 1440 can be another capacitor that is identical to the
capacitor 1426, or the module 1440 can be an electrically inactive
element. Suitable electrically inactive modules include ceramic
blocks shaped like the capacitor 1426 and located with respect to
the coil 1422, the core 1428 and the imaging element 1430 to be
symmetrical with each other. In still other embodiments the module
1440 can be a different type of electrically active element
electrically coupled to the magnetic transponder 1420.
[0112] One specific process of using the marker involves imaging
the marker using a first modality and then tracking the target of
the patient and/or the marker using a second modality. For example,
the location of the marker relative to the target can be determined
by imaging the marker and the target using radiation. The marker
and/or the target can then be localized and tracked using the
magnetic field generated by the marker in response to an excitation
energy.
[0113] The marker 1400 shown in FIGS. 14A-B is expected to provide
an enhanced radiographic image compared to conventional magnetic
markers for more accurately determining the relative position
between the marker and the target of a patient. FIG. 14C, for
example, illustrates a radiographic image 1450 of the marker 1400
and a target T of the patient. The first and second contrast
elements 1432 and 1434 are expected to be more distinct in the
radiographic image 1450 because they can be composed of higher
density materials than the components of the magnetic transponder
1420. The first and second contrast elements 1432 and 1434 can
accordingly appear as bulbous ends of a dumbbell shape in
applications in which the components of the magnetic transponder
1420 are visible in the image. In certain megavolt applications,
the components of the magnetic transponder 1420 may not appear at
all on the radiographic image 1450 such that the first and second
contrast elements 1432 and 1434 will appear as distinct regions
that are separate from each other. In either embodiment, the first
and second contrast elements 1432 and 1434 provide a reference
frame in which the radiographic centroid R.sub.c of the marker 1400
can be located in the image 1450. Moreover, because the imaging
element 1430 is configured so that the radiographic centroid
R.sub.c is at least approximately coincident with the magnetic
centroid M.sub.c, the relative offset or position between the
target T and the magnetic centroid M.sub.c can be accurately
determined using the marker 1400. The embodiment of the marker 1400
illustrated in FIGS. 14A-C, therefore, is expected to mitigate
errors caused by incorrectly estimating the radiographic and
magnetic centroids of markers in radiographic images.
[0114] FIG. 15A is an isometric view of a marker 1500 with a
cut-away portion to illustrate internal components, and FIG. 15B is
a cross-sectional view of the marker 1500 taken along line 15B-15B
of FIG. 15A. The marker 1500 is similar to the marker 1400 shown
above in FIG. 14A, and thus like reference numbers refer to like
components. The marker 1500 differs from the marker 1400 in that
the marker 1500 includes an imaging element 1530 defined by a
single contrast element. The imaging element 1530 is generally
configured relative to the magnetic transponder 1420 so that the
radiographic centroid of the marker 1500 is at least approximately
coincident with the magnetic centroid of the magnetic transponder
1420. The imaging element 1530, more specifically, is a ring
extending around the coil 1422 at a medial region of the magnetic
transponder 1420. The imaging element 1530 can be composed of the
same materials described above with respect to the imaging element
1430 in FIGS. 14A-B. The imaging element 1530 can have an inner
diameter that is approximately equal to the outer diameter of the
coil 1422, and an outer diameter within the casing 1410. As shown
in FIG. 15B, however, a spacer 1531 can be between the inner
diameter of the imaging element 1530 and the outer diameter of the
coil 1422.
[0115] The marker 1500 is expected to operate in a manner similar
to the marker 1400 described above. The marker 1500, however, does
not have two separate contrast elements that provide two distinct,
separate points in a radiographic image. The imaging element 1530
is still highly useful in that it identifies the radiographic
centroid of the marker 1500 in a radiographic image, and it can be
configured so that the radiographic centroid of the marker 1500 is
at least approximately coincident with the magnetic centroid of the
magnetic transponder 1420.
[0116] FIG. 16A is an isometric view of a marker 1600 having a
cut-away portion, and FIG. 16B is a cross-sectional view of the
marker 1600 taken along line 16B-16B of FIG. 16A. The marker 1600
is substantially similar to the marker 1500 shown in FIGS. 15A-B,
and thus like reference numbers refer to like components in FIGS.
14A-16B. The imaging element 1630 can be a high density ring
configured relative to the magnetic transponder 1420 so that the
radiographic centroid of the marker 1600 is at least approximately
coincident with the magnetic centroid of the magnetic transponder
1420. The marker 1600, more specifically, includes an imaging
element 1630 around the casing 1410. The marker 1600 is expected to
operate in much the same manner as the marker 1500 shown in FIGS.
15A-B.
[0117] FIG. 17 is an isometric view with a cut-away portion
illustrating a marker 1700 in accordance with another embodiment of
the invention. The marker 1700 is similar to the marker 1400 shown
in FIGS. 14A-C, and thus like reference numbers refer to like
components in these Figures. The marker 1700 has an imaging element
1730 including a first contrast element 1732 at one end of the
magnetic transponder 1420 and a second contrast element 1734 at
another end of the magnetic transponder 1420. The first and second
contrast elements 1732 and 1734 are spheres composed of suitable
high density materials. The contrast elements 1732 and 1734, for
example, can be composed of gold, tungsten, platinum or other
suitable high-density materials for use in radiographic imaging.
The marker 1700 is expected to operate in a manner similar to the
marker 1400, as described above.
[0118] FIG. 18 is an isometric view with a cut-away portion of a
marker 1800 in accordance with yet another embodiment of the
invention. The marker 1800 is substantially similar to the markers
1400 and 1700 shown in FIGS. 14A and 17, and thus like reference
numbers refer to like components in these Figures. The marker 1800
includes an imaging element 1830 including a first contrast element
1832 and a second contrast element 1834. The first and second
contrast elements 1832 and 1834 can be positioned proximate to
opposing ends of the magnetic transponder 1420. The first and
second contrast elements 1832 and 1834 can be discontinuous rings
having a gap 1835 to mitigate eddy currents. The contrast elements
1832 and 1834 can be composed of the same materials as described
above with respect to the contrast elements of other imaging
elements in accordance with other embodiments of the invention.
[0119] Additional embodiments of markers in accordance with the
invention can include imaging elements incorporated into or
otherwise integrated with the casing 1410, the core 1428 (FIG. 14B)
of the magnetic transponder 1420, and/or the adhesive 1429 (FIG.
14B) in the casing. For example, particles of a high density
material can be mixed with ferrite and extruded to form the core
1428. Alternative embodiments can mix particles of a high density
material with glass or another material to form the casing 1410, or
coat the casing 1410 with a high-density material. In still other
embodiments, a high density material can be mixed with the adhesive
1429 and injected into the casing 1410. Any of these embodiments
can incorporate the high density material into a combination of the
casing 1410, the core 1428 and/or the adhesive 1429. Suitable high
density materials can include tungsten, gold and/or platinum as
described above.
[0120] The markers described above with reference to FIGS. 14A-18
can be used for the markers 40 in the localization system 10 (FIGS.
7-13). The localization system 10 can have several markers with the
same type of imaging elements, or markers with different imaging
elements can be used with the same instrument. Several additional
details of these markers and other embodiments of markers are
described in U.S. application Ser. Nos. 10/334,698 and 10/746,888,
which are incorporated herein by reference. For example, the
markers may not have any imaging elements for applications with
lower energy radiation, or the markers may have reduced volumes of
ferrite and metals to mitigate issues with MRI imaging as set forth
in U.S. application Ser. No. 10/334,698.
2. Localization Systems
[0121] FIG. 19 is a schematic block diagram of a localization
system 1900 for determining the absolute location of the markers 40
(shown schematically) relative to a reference frame. The
localization system 1900 includes an excitation source 1910, a
sensor assembly 1912, a signal processor 1914 operatively coupled
to the sensor assembly 1912, and a controller 1916 operatively
coupled to the excitation source 1910 and the signal processor
1914. The excitation source 1910 is one embodiment of the
excitation source 60 described above with reference to FIG. 9; the
sensor assembly 1912 is one embodiment of the sensor assembly 70
described above with reference to FIG. 9; and the controller 1916
is one embodiment of the controller 80 described above with
reference to FIG. 9.
[0122] The excitation source 1910 is adjustable to generate a
magnetic field having a waveform with energy at selected
frequencies to match the resonant frequencies of the markers 40.
The magnetic field generated by the excitation source 1910
energizes the markers at their respective frequencies. After the
markers 40 have been energized, the excitation source 1910 is
momentarily switched to an "off" position so that the pulsed
magnetic excitation field is terminated while the markers
wirelessly transmit the location signals. This allows the sensor
assembly 1912 to sense the location signals from the markers 40
without measurable interference from the significantly more
powerful magnetic field from the excitation source 1910. The
excitation source 1910 accordingly allows the sensor assembly 1912
to measure the location signals from the markers 40 at a sufficient
signal-to-noise ratio so that the signal processor 1914 or the
controller 1916 can accurately calculate the absolute location of
the markers 40 relative to a reference frame.
a. Excitation Sources
[0123] Referring still to FIG. 19, the excitation source 1910
includes a high voltage power supply 1940, an energy storage device
1942 coupled to the power supply 1940, and a switching network 1944
coupled to the energy storage device 1942. The excitation source
1910 also includes a coil assembly 1946 coupled to the switching
network 1944. In one embodiment, the power supply 1940 is a 500
volt power supply, although other power supplies with higher or
lower voltages can be used. The energy storage device 1942 in one
embodiment is a high voltage capacitor that can be charged and
maintained at a relatively constant charge by the power supply
1940. The energy storage device 1942 alternately provides energy to
and receives energy from the coils in the coil assembly 1946.
[0124] The energy storage device 1942 is capable of storing
adequate energy to reduce voltage drop in the energy storage device
while having a low series resistance to reduce power losses. The
energy storage device 1942 also has a low series inductance to more
effectively drive the coil assembly 1946. Suitable capacitors for
the energy storage device 1942 include aluminum electrolytic
capacitors used in flash energy applications. Alternative energy
storage devices can also include NiCd and lead acid batteries, as
well as alternative capacitor types, such as tantalum, film, or the
like.
[0125] The switching network 1944 includes individual H-bridge
switches 1950 (identified individually by reference numbers
1950a-d), and the coil assembly 1946 includes individual source
coils 1952 (identified individually by reference numbers 1952a-d).
Each H-bridge switch 1950 controls the energy flow between the
energy storage device 1942 and one of the source coils 1952. For
example, H-bridge switch #1 1950a independently controls the flow
of the energy to/from source coil #1 1952a, H-bridge switch #2
1950b independently controls the flow of the energy to/from source
coil #2 1952b, H-bridge switch #3 1950c independently controls the
flow of the energy to/from source coil #3 1952c, and H-bridge
switch #4 1950d independently controls the flow of the energy
to/from source coil #4 1952d. The switching network 1944
accordingly controls the phase of the magnetic field generated by
each of the source coils 1952a-d independently. The H-bridges 1950
can be configured so that the electrical signals for all the source
coils 1952 are in phase, or the H-bridge switches 1950 can be
configured so that one or more of the source coils 1952 are
180.degree. out of phase. Furthermore, the H-bridge switches 1950
can be configured so that the electrical signals for one or more of
the source coils 1952 are between 0 and 180.degree. out of phase to
simultaneously provide magnetic fields with different phases.
[0126] The source coils 1952 can be arranged in a coplanar array
that is fixed relative to the reference frame. Each source coil
1952 can be a square, planar winding arranged to form a flat,
substantially rectilinear coil. The source coils 1952 can have
other shapes and other configurations in different embodiments. In
one embodiment, the source coils 1952 are individual conductive
lines formed in a stratum of a printed circuit board, or windings
of a wire in a foam frame. Alternatively, the source coils 1952 can
be formed in different substrates or arranged so that two or more
of the source coils are not planar with each other. Additionally,
alternate embodiments of the invention may have fewer or more
source coils than illustrated in FIG. 19.
[0127] The selected magnetic fields from the source coils 1952
combine to form an adjustable excitation field that can have
different three-dimensional shapes to excite the markers 40 at any
spatial orientation within an excitation volume. When the planar
array of the source coils 1952 is generally horizontal, the
excitation volume is positioned above an area approximately
corresponding to the central region of the coil assembly 1946. The
excitation volume is the three-dimensional space adjacent to the
coil assembly 1946 in which the strength of the magnetic field is
sufficient to adequately energize the markers 40.
[0128] FIGS. 20-22 are schematic views of a planar array of the
source coils 1952 with the alternating electrical signals provided
to the source coils in different combinations of phases to generate
excitation fields about different axes relative to the illustrated
XYZ coordinate system. Each source coil 1952 has two outer sides
2012 and two inner sides 2014. Each inner side 2014 of one source
coil 1952 is immediately adjacent to an inner side 2014 of another
source coil 1952, but the outer sides 2012 of all the source coils
1952 are not adjacent to any other source coil 1952.
[0129] In the embodiment of FIG. 20, all the source coils 1952a-d
simultaneously receive an alternating electrical signals in the
same phase. As a result, the electrical current flows in the same
direction through all the source coils 1952a-d such that a
direction 2013 of the current flowing along the inner sides 2014 of
one source coil (e.g., source coil 1952a) is opposite to the
direction 2013 of the current flowing along the inner sides 2014 of
the two adjacent source coils (e.g., source coils 1952c and 1952d).
The magnetic fields generated along the inner sides 2014
accordingly cancel each other out so that the magnetic field is
effectively generated from the current flowing along the outer
sides 2012 of the source coils. The resulting excitation field
formed by the combination of the magnetic fields from the source
coils 1952a-d shown in FIG. 20 has a magnetic moment 2015 generally
in the Z direction within an excitation volume 1109. This
excitation field energizes markers parallel to the Z-axis or
markers positioned with an angular component along the Z-axis
(i.e., not orthogonal to the Z-axis).
[0130] FIG. 21 is a schematic view of the source coils 1952a-d with
the alternating electrical signals provided in a second combination
of phases to generate a second excitation field with a different
spatial orientation. In this embodiment, source coils 1952a and
1952c are in phase with each other, and source coils 1952b and
1952d are in phase with each other. However, source coils 1952a and
1952c are 180 degrees out of phase with source coils 1952b and
1952d. The magnetic fields from the source coils 1952a-d combine to
generate an excitation field having a magnetic moment 2117
generally in the Y direction within the excitation volume 2009.
Accordingly, this excitation field energizes markers parallel to
the Y-axis or markers positioned with an angular component along
the Y-axis.
[0131] FIG. 22 is a schematic view of the source coils 1952a-d with
the alternating electrical signals provided in a third combination
of phases to generate a third excitation field with a different
spatial orientation. In this embodiment, source coils 1952a and
1952b are in phase with each other, and source coils 1952c and
1952d are in phase with each other. However, source coils 1952a and
1952b are 180 degrees out of phase with source coils 1952c and
1952d. The magnetic fields from the source coils 1952a-d combine to
generate an excitation field having a magnetic moment 2219 in the
excitation volume 2009 generally in the direction of the X-axis.
Accordingly, this excitation field energizes markers parallel to
the X-axis or markers positioned with an angular component along
the X-axis.
[0132] FIG. 23 is a schematic view of the source coils 1952a-d
illustrating the current flow to generate an excitation field 2324
for energizing markers 40 with longitudinal axes parallel to the
Y-axis. The switching network 1944 (FIG. 19) is configured so that
the phases of the alternating electrical signals provided to the
source coils 1952a-d are similar to the configuration of FIG. 21.
This generates the excitation field 2324 with a magnetic moment in
the Y direction to energize the markers 40.
[0133] FIG. 24 further illustrates the ability to spatially adjust
the excitation field in a manner that energizes any of the markers
40 at different spatial orientations. In this embodiment, the
switching network 1944 (FIG. 19) is configured so that the phases
of the alternating electrical signals provided to the source coils
1952a-d are similar to the configuration shown in FIG. 20. This
produces an excitation field with a magnetic moment in the Z
direction that energizes markers 40 with longitudinal axes parallel
to the Z-axis.
[0134] The spatial configuration of the excitation field in the
excitation volume 2009 can be quickly adjusted by manipulating the
switching network to change the phases of the electrical signals
provided to the source coils 1952a-d. As a result, the overall
magnetic excitation field can be changed to be oriented in either
the X, Y or Z directions within the excitation volume 2009. This
adjustment of the spatial orientation of the excitation field
reduces or eliminates blind spots in the excitation volume 2009.
Therefore, the markers 40 within the excitation volume 2009 can be
energized by the source coils 1952a-d regardless of the spatial
orientations of the leadless markers.
[0135] In one embodiment, the excitation source 1910 is coupled to
the sensor assembly 1912 so that the switching network 1944 (FIG.
19) adjusts orientation of the pulsed generation of the excitation
field along the X, Y, and Z axes depending upon the strength of the
signal received by the sensor assembly. If the location signal from
a marker 40 is insufficient, the switching network 1944 can
automatically change the spatial orientation of the excitation
field during a subsequent pulsing of the source coils 1952a-d to
generate an excitation field with a moment in the direction of a
different axis or between axes. The switching network 1944 can be
manipulated until the sensor assembly 1912 receives a sufficient
location signal from the marker.
[0136] The excitation source 1910 illustrated in FIG. 19
alternately energizes the source coils 1952a-d during an excitation
phase to power the markers 40, and then actively de-energizes the
source coils 1952a-d during a sensing phase in which the sensor
assembly 1912 senses the decaying location signals wirelessly
transmitted by the markers 40. To actively energize and de-energize
the source coils 1952a-d, the switching network 1944 is configured
to alternatively transfer stored energy from the energy storage
device 1942 to the source coils 1952a-d, and to then re-transfer
energy from the source coils 1952a-d back to the energy storage
device 1942. The switching network 1944 alternates between first
and second "on" positions so that the voltage across the source
coils 1952 alternates between positive and negative polarities. For
example, when the switching network 1944 is switched to the first
"on" position, the energy in the energy storage device 1942 flows
to the source coils 1952a-d. When the switching network 1944 is
switched to the second "on" position, the polarity is reversed such
that the energy in the source coils 1952a-d is actively drawn from
the source coils 1952a-d and directed back to the energy storage
device 1942. As a result, the energy in the source coils 1952a-d is
quickly transferred back to the energy storage device 1942 to
abruptly terminate the excitation field transmitted from the source
coils 1952a-d and to conserve power consumed by the energy storage
device 1942. This removes the excitation energy from the
environment so that the sensor assembly 1912 can sense the location
signals from the markers 40 without interference from the
significantly larger excitation energy from the excitation source
1910. Several additional details of the excitation source 1910 and
alternate embodiments are disclosed in U.S. patent application Ser.
No. 10/213,980 filed on Aug. 7, 2002, and now U.S. Pat. No.
6,822,570, which is incorporated by reference herein in its
entirety.
b. Sensor Assemblies
[0137] FIG. 25A is an exploded isometric view showing several
components of the sensor assembly 1912 for use in the localization
system 1900 (FIG. 19). The sensor assembly 1912 includes a sensing
unit 2501 having a plurality of coils 2502 formed on or carried by
a panel 2504. The coils 2502 can be field sensors or magnetic flux
sensors arranged in a sensor array 2505.
[0138] The panel 2504 may be a substantially non-conductive
material, such as a sheet of KAPTON.RTM. produced by DuPont.
KAPTON.RTM. is particularly useful when an extremely stable, tough,
and thin film is required (such as to avoid radiation beam
contamination), but the panel 2504 may be made from other materials
and have other configurations. For example, FR4 (epoxy-glass
substrates), GETEK or other Teflon-based substrates, and other
commercially available materials can be used for the panel 2504.
Additionally, although the panel 2504 may be a flat, highly planar
structure, in other embodiments, the panel may be curved along at
least one axis. In either embodiment, the field sensors (e.g.,
coils) are arranged in a locally planar array in which the plane of
one field sensor is at least substantially coplanar with the planes
of adjacent field sensors. For example, the angle between the plane
defined by one coil relative to the planes defined by adjacent
coils can be from approximately 0.degree. to 10.degree., and more
generally is less than 5.degree.. In some circumstances, however,
one or more of the coils may be at an angle greater than 10.degree.
relative to other coils in the array.
[0139] The sensor assembly 1912 shown in FIG. 25A can optionally
include a core 2520 laminated to the panel 2504. The core 2520 can
be a support member made from a rigid material, or the core 2520
can be a low density foam, such as a closed-cell Rohacell foam. The
core 2520 is preferably a stable layer that has a low coefficient
of thermal expansion so that the shape of the sensor assembly 1912
and the relative orientation between the coils 2502 remain within a
defined range over an operating temperature range.
[0140] The sensor assembly 1912 can further include a first
exterior cover 2530a on one side of the sensing subsystem and a
second exterior cover 2530b on an opposing side. The first and
second exterior covers 2530a-b can be thin, thermally stable
layers, such as Kevlar or Thermount films. Each of the first and
second exterior covers 2530a-b can include electric shielding 2532
to block undesirable external electric fields from reaching the
coils 2502. The electric shielding 2532 can be a plurality of
parallel legs of gold-plated, copper strips to define a comb-shaped
shield in a configuration commonly called a Faraday shield. It will
be appreciated that the shielding can be formed from other
materials that are suitable for shielding. The electric shielding
can be formed on the first and second exterior covers using printed
circuit board manufacturing technology or other techniques.
[0141] The panel 2504 with the coils 2502 is laminated to the core
2520 using a pressure sensitive adhesive or another type of
adhesive. The first and second exterior covers 2530a-b are
similarly laminated to the assembly of the panel 2504 and the core
2520. The laminated assembly forms a rigid structure that fixedly
retains the arrangement of the coils 2502 in a defined
configuration over a large operating temperature range. As such,
the sensor assembly 1912 does not substantially deflect across its
surface during operation. The sensor assembly 1912, for example,
can retain the array of coils 2502 in the fixed position with a
deflection of no greater than .+-.0.5 mm, and in some cases no more
than .+-.0.3 mm. The stiffness of the sensing subsystem provides
very accurate and repeatable monitoring of the precise location of
leadless markers in real time.
[0142] In still another embodiment, the sensor assembly 1912 can
further include a plurality of source coils that are a component of
the excitation source 1910. One suitable array combining the sensor
assembly 1912 with source coils is disclosed in U.S. patent
application Ser. No. 10/334,700, entitled PANEL-TYPE SENSOR/SOURCE
ARRAY ASSEMBLY, filed on Dec. 30, 2002, which is herein
incorporated by reference.
[0143] FIG. 25B further illustrates an embodiment of the sensing
unit 2501. In this embodiment, the sensing unit 2501 includes 32
sensor coils 2502; each coil 2502 is associated with a separate
channel 2506 (shown individually as channels "Ch 0" through "Ch
31"). The overall dimension of the panel 2504 can be approximately
40 cm by 54 cm, but the array 2505 has a first dimension D1 of
approximately 40 cm and a second dimension D2 of approximately 40
cm. The array 2505 can have other sizes or other configurations
(e.g., circular) in alternative embodiments. Additionally, the
array 2505 can have more or fewer coils, such as 8-64 coils; the
number of coils may moreover be a power of 2.
[0144] The coils 2502 may be conductive traces or depositions of
copper or another suitably conductive metal formed on the panel
2504. Each coil 2502 has a trace with a width of approximately 0.15
mm and a spacing between adjacent turns within each coil of
approximately 0.13 mm. The coils 2502 can have approximately 15 to
90 turns, and in specific applications each coil has approximately
40 turns. Coils with less than 15 turns may not be sensitive enough
for some applications, and coils with more than 90 turns may lead
to excessive voltage from the source signal during excitation and
excessive settling times resulting from the coil's lower
self-resonant frequency. In other applications, however, the coils
2502 can have less than 15 turns or more than 90 turns.
[0145] As shown in FIG. 25B, the coils 2502 are arranged as square
spirals, although other configurations may be employed, such as
arrays of circles, interlocking hexagons, triangles, etc. Such
square spirals utilize a large percentage of the surface area to
improve the signal to noise ratio. Square coils also simplify
design layout and modeling of the array compared to circular coils;
for example, circular coils could waste surface area for linking
magnetic flux from the markers 40. The coils 2502 have an inner
dimension of approximately 40 mm, and an outer dimension of
approximately 62 mm, although other dimensions are possible
depending upon applications. Sensitivity may be improved with an
inner dimension as close to an outer dimension as possible given
manufacturing tolerances. In several embodiments, the coils 2502
are identical to each other or at least configured substantially
similarly.
[0146] The pitch of the coils 2502 in the array 2505 is a function
of, at least in part, the minimum distance between the marker and
the coil array. In one embodiment, the coils are arranged at a
pitch of approximately 67 mm. This specific arrangement is
particularly suitable when the wireless markers 40 are positioned
approximately 7-27 cm from the sensor assembly 1912. If the
wireless markers are closer than 7 cm, then the sensing subsystem
may include sensor coils arranged at a smaller pitch. In general, a
smaller pitch is desirable when wireless markers are to be sensed
at a relatively short distance from the array of coils. The pitch
of the coils 2502, for example, is approximately 50%-200% of the
minimum distance between the marker and the array.
[0147] In general, the size and configuration of the array 2505 and
the coils 2502 in the array depend on the frequency range in which
they are to operate, the distance from the markers 40 to the array,
the signal strength of the markers, and several other factors.
Those skilled in the relevant art will readily recognize that other
dimensions and configurations may be employed depending, at least
in part, on a desired frequency range and distance from the markers
to the coils.
[0148] The array 2505 is sized to provide a large aperture to
measure the magnetic field emitted by the markers. It can be
particularly challenging to accurately measure the signal emitted
by an implantable marker that wirelessly transmits a marker signal
in response to a wirelessly transmitted energy source because the
marker signal is much smaller than the source signal and other
magnetic fields in a room (e.g., magnetic fields from CRTs, etc.).
The size of the array 2505 can be selected to preferentially
measure the near field of the marker while mitigating interference
from far field sources. In one embodiment, the array 2505 is sized
to have a maximum dimension D1 or D2 across the surface of the area
occupied by the coils that is approximately 100% to 300% of a
predetermined maximum sensing distance that the markers are to be
spaced from the plane of the coils. Thus, the size of the array
2505 is determined by identifying the distance that the marker is
to be spaced apart from the array to accurately measure the marker
signal, and then arrange the coils so that the maximum dimension of
the array is approximately 100% to 300% of that distance. The
maximum dimension of the array 2505, for example, can be
approximately 200% of the sensing distance at which a marker is to
be placed from the array 2505. In one specific embodiment, the
marker 40 has a sensing distance of 20 cm and the maximum dimension
of the array of coils 2502 is between 20 cm and 60 cm, and more
specifically 40 cm.
[0149] A coil array with a maximum dimension as set forth above is
particularly useful because it inherently provides a filter that
mitigates interference from far field sources. As such, one aspect
of several embodiments of the invention is to size the array based
upon the signal from the marker so that the array preferentially
measures near field sources (i.e., the field generated by the
marker) and filters interference from far field sources.
[0150] The coils 2502 are electromagnetic field sensors that
receive magnetic flux produced by the wireless markers 40 and in
turn produce a current signal representing or proportional to an
amount or magnitude of a component of the magnetic field through an
inner portion or area of each coil. The field component is also
perpendicular to the plane of each coil 2502. Each coil represents
a separate channel, and thus each coil outputs signals to one of 32
output ports 2506. A preamplifier, described below, may be provided
at each output port 2506. Placing preamplifiers (or impedance
buffers) close to the coils minimizes capacitive loading on the
coils, as described herein. Although not shown, the sensing unit
2501 also includes conductive traces or conductive paths routing
signals from each coil 2502 to its corresponding output port 2506
to thereby define a separate channel. The ports in turn are coupled
to a connector 2508 formed on the panel 2504 to which an
appropriately configured plug and associated cable may be
attached.
[0151] The sensing unit 2501 may also include an onboard memory or
other circuitry, such as shown by electrically erasable
programmable read-only memory (EEPROM) 2510. The EEPROM 2510 may
store manufacturing information such as a serial number, revision
number, date of manufacture, and the like. The EEPROM 2510 may also
store per-channel calibration data, as well as a record of
run-time. The run-time will give an indication of the total
radiation dose to which the array has been exposed, which can alert
the system when a replacement sensing subsystem is required.
[0152] Although shown in one plane only, additional coils or
electromagnetic field sensors may be arranged perpendicular to the
panel 2504 to help determine a three-dimensional location of the
wireless markers 40. Adding coils or sensors in other dimensions
could increase the total energy received from the wireless markers
40, but the complexity of such an array would increase
disproportionately. The inventors have found that three-dimensional
coordinates of the wireless markers 40 may be found using the
planar array shown in FIGS. 25A-B.
[0153] Implementing the sensor assembly 1012 may involve several
considerations. First, the coils 2502 may not be presented with an
ideal open circuit. Instead, they may well be loaded by parasitic
capacitance due largely to traces or conductive paths connecting
the coils 2502 to the preamplifiers, as well as a damping network
(described below) and an input impedance of the preamplifiers
(although a low input impedance is preferred). These combined loads
result in current flow when the coils 2502 link with a changing
magnetic flux. Any one coil 2502, then, links magnetic flux not
only from the wireless marker 40, but also from all the other coils
as well. These current flows should be accounted for in downstream
signal processing.
[0154] A second consideration is the capacitive loading on the
coils 2502. In general, it is desirable to minimize the capacitive
loading on the coils 2502. Capacitive loading forms a resonant
circuit with the coils themselves, which leads to excessive voltage
overshoot when the excitation source 1910 is energized. Such a
voltage overshoot should be limited or attenuated with a damping or
"snubbing" network across the coils 2502. A greater capacitive
loading requires a lower impedance damping network, which can
result in substantial power dissipation and heating in the damping
network.
[0155] Another consideration is to employ preamplifiers that are
low noise. The preamplification can also be radiation tolerant
because one application for the sensor assembly 1912 is with
radiation therapy systems that use linear accelerators (LINAC). As
a result, PNP bipolar transistors and discrete elements may be
preferred. Further, a DC coupled circuit may be preferred if good
settling times cannot be achieved with an AC circuit or output,
particularly if analog to digital converters are unable to handle
wide swings in an AC output signal.
[0156] FIG. 26, for example, illustrates an embodiment of a
snubbing network 2602 having a differential amplifier 2604. The
snubbing network 2602 includes two pairs of series coupled
resistors and a capacitor bridging therebetween. A biasing circuit
2606 allows for adjustment of the differential amplifier, while a
calibration input 2608 allows both input legs of the differential
amplifier to be balanced. The coil 2502 is coupled to an input of
the differential amplifier 2604, followed by a pair of high voltage
protection diodes 2610. DC offset may be adjusted by a pair of
resistors coupled to bases of the input transistors for the
differential amplifier 2604 (shown as having a zero value).
Additional protection circuitry is provided, such as ESD protection
diodes 2612 at the output, as well as filtering capacitors (shown
as having a 10 nF value).
c. Signal Processors and Controllers
[0157] The signal processor 1914 and the controller 1916
illustrated in FIG. 16 receive the signals from the sensor assembly
1912 and calculate the absolute positions of the markers 40 within
the reference frame. Suitable signal processing systems and
algorithms are set forth in U.S. application Ser. Nos. 10/679,801;
10/749,478; 10/750,456; 10/750,164; 10/750,165; 10/749,860; and
10/750,453, all of which are incorporated herein by reference.
EXAMPLE
Overview
[0158] An experimental phantom based study was conducted to
determine effectiveness of this system for real-time tracking. In
this experiment, a custom 4D stage was constructed to allow
arbitrary motion in three axes for speeds up to 10 cm/sec in each
dimension, with accuracy to 0.3 mm. Position accuracy was measured
by a 3D digitizing arm attached to the stage system. As shown in
FIG. 27, two ellipses were created with peak to peak motion of 2
cm, 4 cm and 2 cm; and 1 cm by 2 cm and 1 cm in the x, y and z
direction respectively. Three periods were used to correspond to
15, 17 and 20 breaths per minute. A single transponder was used
with an integration time of 33 ms, 67 ms and 100 ms and two
transponders were used with integration times of 67 ms and 100 ms.
The transponders were placed in a custom phantom mounted to the 4D
stage. The experiment was performed with the isocenter placed 14 cm
from the AC magnetic array to simulate the position of an average
lung cancer patient. The 4D stage ran each trajectory while the
real time tracking system measured the transponder positions.
Measured position was compared against the phantom position. The
effects of ellipse size, speed, transponder number and integration
time were characterized.
Experiment Summary
[0159] As shown in FIG. 28, the root mean square (RMS) error was
less than 1 mm for each ellipse, period and transponder integration
time. The system was able to track points throughout the path of
the ellipse, for example, in a trajectory of a large ellipse moving
at 17 breaths per minute. FIG. 29 is a histogram of localization
errors illustrating that the range of error was low for each point
measured. As shown in FIG. 30, the RMS error was higher in areas of
increased velocity in most trajectories. With respect to this
experiment, a single transponder system performed slightly better
than dual transponder systems, with the best system being a single
transponder with a 67 ms integration time.
CONCLUSION
[0160] Those skilled in the art will appreciate that the
above-described facility may be straightforwardly adapted or
extended in various ways. For example, the facility may operate in
a wide variety of radiation treatment and treatment planning
environments, and in conjunction with a wide variety of different
patient tracking technologies. The facility may use a set of
modules that is different from those shown and described herein.
The facility may use a variety of different communication
mechanisms to communicate patient position information. Patient
position information may be provided to various consumers at
various different levels of latency and/or frequency. In some
embodiments, the facility can be used to perform patient tracking
at times when the patient is not being subjected to radiation
therapy treatment, such as (1) to position the patient before
radiation therapy commences, or (2) to observe changes in the
location, volume, shape, and/or orientation of the patient's tumor
outside the radiation therapy vault. While the foregoing
description makes reference to preferred embodiments, the scope of
the invention is defined solely by the claims that follow and the
elements recited therein.
* * * * *