U.S. patent application number 13/897085 was filed with the patent office on 2013-09-26 for particle beam therapy system.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Hisashi Harada, Takaaki IWATA, Kengo Sugahara.
Application Number | 20130253845 13/897085 |
Document ID | / |
Family ID | 46651983 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130253845 |
Kind Code |
A1 |
IWATA; Takaaki ; et
al. |
September 26, 2013 |
PARTICLE BEAM THERAPY SYSTEM
Abstract
The objective is to eliminate the effect of the hysteresis of a
scanning electromagnet and resume high-accuracy beam irradiation
from an irradiation position where it has been interrupted, even in
the case where emergency-stop processing is performed during
therapy. There are provided an irradiation management apparatus
that controls a scanning electromagnet; and an interlock
information inputting device that generates an interlock signal for
stopping irradiation of the charged particle beam, when a
contingency occurs. When irradiation of the charged particle beam
is resumed, the irradiation management apparatus performs idle
operation in which the scanning electromagnet is controlled, with
the charged particle beam unirradiated, from a start step, which is
situated prior to a stop step and is different from the initial
step in actual irradiation, to the stop step, and then irradiates
the charged particle beam from the desired irradiation position
coordinates corresponding to the stop step.
Inventors: |
IWATA; Takaaki; (Tokyo,
JP) ; Sugahara; Kengo; (Tokyo, JP) ; Harada;
Hisashi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Chiyoda-ku
JP
|
Family ID: |
46651983 |
Appl. No.: |
13/897085 |
Filed: |
May 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13258240 |
Sep 21, 2011 |
8466441 |
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PCT/JP2011/053367 |
Feb 17, 2011 |
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13897085 |
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Current U.S.
Class: |
702/19 |
Current CPC
Class: |
A61N 2005/1074 20130101;
A61B 5/48 20130101; A61N 2005/1087 20130101; A61N 5/1043
20130101 |
Class at
Publication: |
702/19 |
International
Class: |
A61B 5/00 20060101
A61B005/00 |
Claims
1. A patient respiration evaluation method in which a displacement
between a real respiratory signal indicating real respiration of a
patient and a reference respiratory signal indicating desired
respiration of the patient is evaluated, the patient respiration
evaluation method comprising: a step of obtaining a first gain and
a first phase of a describing function corresponding to a
first-order term in a Fourier series expansion of the reference
respiratory signal; a step of obtaining a second gain and a second
phase of a describing function corresponding to a first-order term
in a Fourier series expansion of the real respiratory signal; and a
step of comparing the first gain with the second gain and/or
comparing the first phase with the second phase.
2. The patient respiration evaluation method according to claim 1,
further including a step of determining that in the case where the
second gain abruptly falls out of a preliminarily set gain
threshold range around the first gain and/or the second phase
abruptly falls out of a preliminarily set phase threshold range
around the first phase, the patient had a fit of coughing.
3. The patient respiration evaluation method according to claim 1,
further including a step of determining that in the case where the
second gain gradually decreases within the preliminarily set gain
threshold range around the first gain or the correlation between
the second phase and the first phase decreases in such a way as to
exceed a preliminarily set correlation determination range, it is
suggested that the patient has fallen asleep or is going to fall
asleep.
4. A patient respiration evaluation apparatus in which a
displacement between a real respiratory signal indicating real
respiration of a patient and a reference respiratory signal
indicating desired respiration of the patient is evaluated, the
patient respiration evaluation apparatus comprising: a gain
calculation unit that obtains a first gain and a first phase of a
describing function corresponding to a first-order term in a
Fourier series expansion of the reference respiratory signal; a
phase calculation unit that obtains a second gain and a second
phase of a describing function corresponding to a first-order term
in a Fourier series expansion of the real respiratory signal; and a
comparison unit that compares the first gain with the second gain
and/or that compares the first phase with the second phase.
5. The patient respiration evaluation apparatus according to claim
4, further including a determination unit that determines that in
the case where the second gain abruptly falls out of a
preliminarily set gain threshold range around the first gain and/or
the second phase abruptly falls out of a preliminarily set phase
threshold range around the first phase, the patient had a fit of
coughing.
6. The patient respiration evaluation apparatus according to claim
4, further including a determination unit that determines that in
the case where the second gain gradually decreases within the
preliminarily set gain threshold range around the first gain or the
correlation between the second phase and the first phase decreases
in such a way as to exceed a preliminarily set correlation
determination range, it is suggested that the patient has fallen
asleep or is going to fall asleep.
Description
TECHNICAL FIELD
[0001] The present invention relates to a particle beam therapy
system utilized in the medical field and R&Ds and particularly
to a particle beam therapy system of a scanning type such as a
spot-scanning type or a raster-scanning type.
BACKGROUND ART
[0002] In general, a particle beam therapy system is provided with
a beam generation apparatus that generates a charged particle beam;
an accelerator that is connected with the beam generation apparatus
and accelerates a generated charged particle beam; a beam transport
system that transports a charged particle beam that is accelerated
by the accelerator so as to gain predetermined energy and then
emitted; and a particle beam irradiation apparatus, disposed at the
downstream side of the beam transport system, for irradiating a
charged particle beam onto an irradiation subject, which is a
diseased site of a patient or the like. Particle beam irradiation
apparatuses are roughly divided into apparatuses utilizing a broad
irradiation method in which a charged particle beam is enlarged in
a dispersion manner by a scatterer, and the shape of the enlarged
charged particle beam is made to coincide with the shape of an
irradiation subject in order to form an irradiation field; and
apparatuses utilizing a scanning irradiation method (the
spot-scanning method, the raster-scanning method, and the like) in
which an irradiation field is formed by performing scanning with a
thin, pencil-like beam in such a way that the scanning area
coincides with the shape of an irradiation subject.
[0003] In the broad irradiation method, an irradiation field that
coincides with the shape of a diseased site is formed by use of a
collimator or a bolus. The broad irradiation method is a most
universally utilized and superior irradiation method where an
irradiation field that coincides with the shape of a diseased site
is formed so as to prevent unnecessary irradiation onto a normal
tissue. However, it is required to create a bolus for each patient
or to change the shape of a collimator in accordance with a
diseased site.
[0004] In contrast, the scanning irradiation method is a
high-flexibility irradiation method where, for example, neither
collimator nor bolus is required. However, because these components
for preventing irradiation onto not a diseased site but a normal
tissue are not utilized, there is required a positional accuracy of
beam irradiation that is the same as or higher than that of the
broad irradiation method.
[0005] Patent Document 1 discloses the following invention whose
objective is to reduce the effect of the hysteresis of a scanning
electromagnet for scanning a charged particle beam and to realize
high-accuracy beam irradiation. The invention disclosed in Patent
Document 1 includes an irradiation management apparatus that
controls a scanning electromagnet, based on the desired irradiation
position coordinates of a charged particle beam, and a position
monitor that measures the measured position coordinates of the
charged particle beam.
[0006] The irradiation management apparatus is provided with a
command value generator that outputs a control input to the
scanning electromagnet, based on the desired irradiation position
coordinates and correction data generated on the basis of the
measured position coordinates, measured by the position monitor in
preliminary irradiation in which the excitation pattern of the
scanning electromagnet is the same as that of a actual irradiation
plan, and the desired irradiation position coordinates.
[0007] Accordingly, in the invention disclosed in Patent Document
1, the scanning-electromagnet excitation pattern of the preliminary
irradiation is the same as that of the planned actual irradiation,
and the control input to the scanning electromagnet is
preliminarily corrected based on the result obtained in the
preliminary irradiation; therefore, the effect of the hysteresis of
the scanning electromagnet is eliminated, so that high-accuracy
beam irradiation can be realized.
PRIOR ART REFERENCE
Patent Document
[0008] [Patent Document 1] Japanese Patent No. 4532606 (FIGS. 1 and
2)
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0009] In the invention disclosed in Patent Document 1, correction
is preliminarily performed based on the preliminary irradiation,
the scanning-electromagnet excitation pattern for which is the same
as that for actual irradiation; therefore, there is demonstrated an
extra effect that high-accuracy beam irradiation is realized in the
actual irradiation. It is true that when therapy is implemented
normally, the invention disclosed in Patent Document 1 poses no
problem. However, in a therapy scene, due to a contingency where
the size of a charged particle beam exceeds the tolerance range or
a patient gets sick, there may occur a situation in which
irradiation needs to be interrupted, i.e., emergency-stop
processing for the particle beam therapy system needs to be
implemented.
[0010] In this case, emergency-stop processing is implemented so as
to temporarily stop irradiation of a charged particle beam. Because
the diseased site has partly been irradiated with a charged
particle beam, it is required that the irradiation of a charged
particle beam is resumed from an irradiation position where it has
been interrupted, thereby giving a dose planed through a treatment
plan to the whole diseased site. In this situation, provided the
irradiation is resumed simply from the irradiation position where
it has been interrupted, the irradiation pattern of the scanning
electromagnet is resumed from the middle thereof. As a result,
because the hysteresis affects the scanning electromagnet, the
state of the scanning electromagnet at a time when the irradiation
is interrupted differs from the state thereof at a time when the
irradiation is not interrupted; thus, there has been a problem that
while the state of the scanning electromagnet is left different,
the actual irradiation is resumed, a charged particle beam is
irradiated onto a position that is different from the position at a
time when the irradiation is not interrupted, and hence
high-accuracy beam irradiation cannot be performed.
[0011] The present invention has been implemented in order to solve
the foregoing problems; the objective thereof is to obtain a
particle beam therapy system that eliminates the effect of the
hysteresis of a scanning electromagnet and can resume high-accuracy
beam irradiation from an irradiation position where it has been
interrupted.
Means for Solving the Problems
[0012] There are provided an irradiation management apparatus that
controls a scanning electromagnet, based on desired irradiation
position coordinates of a charged particle beam; and an interlock
information inputting device that generates an interlock signal for
stopping irradiation of the charged particle beam, when a
contingency occurs. The irradiation management apparatus is
provided with a command value generator that outputs a control
input to the scanning electromagnet; and a stop step storage memory
that stores a stop step corresponding to the desired irradiation
position coordinates at which irradiation of the charged particle
beam stops, when the interlock signal is generated by the interlock
information inputting device. When irradiation of the charged
particle beam is resumed, the irradiation management apparatus
performs idle operation in which the scanning electromagnet is
controlled, with the charged particle beam unirradiated, from a
start step, which is situated prior to the stop step and is
different from the initial step corresponding to the initial
desired irradiation position coordinates in actual irradiation, to
the stop step, and then irradiates the charged particle beam from
the desired irradiation position coordinates corresponding to the
stop step.
ADVANTAGE OF THE INVENTION
[0013] In the case where emergency-stop processing is performed
during therapy, a particle beam therapy system according to the
present invention carries out idle operation, based on irradiation
command data including a control input to the scanning
electromagnet, from a start step, which is situated prior to the
stop step and is different from the initial step, and starts beam
irradiation from an irradiation position where the irradiation has
been interrupted; therefore, the effect of the hysteresis of the
scanning electromagnet is eliminated, so that high-accuracy beam
irradiation can be resumed from the irradiation position where the
irradiation has been interrupted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a configuration diagram illustrating a particle
beam therapy system according to Embodiment 1 of the present
invention;
[0015] FIG. 2 is a schematic configuration diagram of an
accelerator in FIG. 1;
[0016] FIG. 3 is a schematic configuration diagram of a particle
beam irradiation apparatus in FIG. 1;
[0017] FIG. 4 is a control block diagram illustrating a particle
beam therapy system according to Embodiment 1 of the present
invention;
[0018] FIG. 5 is a graph for explaining a method of correcting a
command current;
[0019] FIG. 6 is a flowchart representing a procedure for stopping
and resuming beam irradiation in a particle beam therapy system
according to Embodiment 1 of the present invention;
[0020] FIG. 7A is a chart representing a reference respiratory
signal;
[0021] FIG. 7B is a chart representing a real respiratory
signal;
[0022] FIG. 8 is a schematic diagram representing a fact that a
diseases site is scanned with a beam along a beam path in a
particle beam therapy system according to Embodiment 2 of the
present invention;
[0023] FIG. 9A and FIG. 9B are charts representing the hysteresis
characteristics of a scanning electromagnet in a particle beam
therapy system according to Embodiment 2 of the present
invention;
[0024] FIG. 10 is a flowchart representing a procedure for stopping
and resuming beam irradiation in a particle beam therapy system
according to Embodiment 2 of the present invention; and
[0025] FIG. 11 is a flowchart representing another procedure for
stopping and resuming beam irradiation in a particle beam therapy
system according to Embodiment 2 of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
[0026] The configuration of a particle beam therapy system
according to Embodiment 1 of the present invention will be
explained below. FIG. 1 is a configuration diagram illustrating a
particle beam therapy system according to Embodiment 1 of the
present invention. FIG. 2 is a schematic configuration diagram of
an accelerator; FIG. 3 is a schematic configuration diagram of a
particle beam irradiation apparatus. FIG. 4 is a control block
diagram illustrating a particle beam therapy system according to
Embodiment 1 of the present invention.
[0027] At first, the outline of the configuration of a particle
beam therapy system will be schematically explained with reference
to FIG. 1. A particle beam therapy system 51 includes a beam
generation apparatus 52, a beam transport system 59, and particle
beam irradiation apparatuses 58a and 58b. The beam generation
apparatus 52 includes an ion source (unillustrated), a prestage
accelerator 53, and a circular accelerator (simply referred to as
an accelerator, hereinafter) 54, which is a synchrotron. The
particle beam irradiation apparatus 58b is provided in a rotating
gantry (unillustrated). The particle beam irradiation apparatus 58a
is provided in a treatment room where no rotating gantry is
installed. The function of the beam transport system 59 is to
achieve communication between the accelerator 54 and the particle
beam irradiation apparatuses 58a and 58b. Part of the beam
transport system 59 is provided in the rotating gantry
(unillustrated), and that part includes a plurality of deflection
electromagnets 55a, 55b, and 55c. The beam generation apparatus 52,
the beam transport system 59, and the particle beam irradiation
apparatuses 58a and 58b are controlled by a control system in a
collaborative manner.
[0028] A charged particle beam 1, which is a particle beam such as
a proton beam generated in ion source or a carbon beam (heavy
particle beam), is accelerated by the prestage accelerator 53 and
enters the accelerator 54. The particle beam 1 is accelerated to
obtain predetermined energy. The charged particle beam 1 is
accelerated by the accelerator 54 in a high-frequency electric
field up to 70% to 80% of the light velocity, as it is being bent
by means of the magnets. The charged particle beam 1 launched from
the accelerator 54 is transported to the particle beam irradiation
apparatuses 58a and 58b by way of the beam transport system 59. In
the beam transport system 59, the charged particle beam 1 that has
received sufficient energy is guided through a path created with a
vacuum duct to the particle beam irradiation apparatuses 58a and
58b in respective designated treatment rooms, while its orbit is
changed by the electromagnets, as may be necessary. The particle
beam irradiation apparatuses 58a and 58b each form an irradiation
field in accordance with the size and the depth of the diseased
site of a patient 24 as an irradiation subject 15, and each
irradiate the charged particle beam 1 onto the irradiation subject
15 (refer to FIG. 3).
[0029] Meanwhile, in the foregoing sentence, the phrase "respective
designated treatment rooms" has been described; in general, in view
of the therapy efficiency, a particle beam therapy system has a
plurality of treatment rooms. That is to say, it is required to
provide particle beam irradiation apparatuses 58 as many as the
number of treatment rooms. In many cases, a large-size complex
system configured with a plurality of subsystems, in general,
includes a sub-controller that is dedicated to control of each
subsystem and a main controller that conducts and controls the
whole system. The particle beam therapy system 51 according to
Embodiment 1 of the present invention will be explained based also
on a case where this configuration with a main controller and a
sub-controller is adopted. For the sake of simplicity, the beam
generation apparatus 52 and the beam transport system 59 will be
herein referred to as an accelerator system 60. The system
consisting of the particle beam irradiation apparatus 58 and the
rotating gantry will be referred to as an "irradiation system".
FIG. 1 illustrates a case where there exist two treatment rooms,
i.e., a horizontal irradiation room and a gantry irradiation room.
The foregoing controller that controls the accelerator system and
the irradiation system in a collaborative manner is a control
system of the particle beam therapy system.
<Accelerator>
[0030] The accelerator 54 will be explained with reference to FIG.
2. The accelerator 54 is provided with a vacuum duct 61 that serves
as an orbit path through which the charged particle beam 1
circulates; an injector 62 for injecting the charged particle beam
1, supplied from a prestage accelerator 53, into the vacuum duct
61; deflection electromagnets 63a, 63b, 63c, and 63d for deflecting
the orbits of charged particles so that the charged particles form
the charged particle beam 1 that circulates along a circulation
orbit in the vacuum duct 61; convergence electromagnets 64a, 64b,
64c, and 64d for converging the charged particle beam 1 formed on
the circulation orbit not to diverge; a high-frequency wave
acceleration cavity 65 that applies a high-frequency voltage,
synchronized with circulating charged particles, to the circulating
charged particles so as to accelerate the charged particles; an
emission apparatus 66 for extracting from the accelerator 54 the
charged particle beam 1 accelerated in the accelerator 54 and
emitting the extracted charged particle beam 1 into the beam
transport system 59; and a six-pole electromagnet 67 that excites
resonance in the circulation orbit of the charged particle beam 1
in order to make the emission apparatus 66 emit the charged
particle beam 1.
[0031] There are provided unillustrated apparatuses for controlling
the respective units; for example, in the deflection electromagnets
63a, 63b, 63c, and 63d, there are provided deflection electromagnet
control apparatuses that control the excitation currents for the
deflection electromagnets 63a, 63b, 63c, and 63d, respectively, and
in the high-frequency wave acceleration cavity 65, there are
provided a high-frequency wave source for supplying a
high-frequency voltage to the high-frequency wave acceleration
cavity 65 and a high-frequency wave control apparatus for
controlling the high-frequency wave source; in the control system,
there is provided an accelerator control apparatus that controls
the whole accelerator by controlling other components such as the
deflection electromagnet control apparatus, the high-frequency wave
control apparatus, and the convergence electromagnet 64a, 64b, 64c,
and 64d. However, in the technical idea of the present invention,
the control of the accelerator itself is not limited; therefore,
the accelerator is not limited to the one having the foregoing
configuration, and it goes without saying that various
modifications are allowed, as long as the variants can stably emit
the charged particle beam 1 into the beam transport system 59.
<Beam Transport System>
[0032] The charged particle beam 1 accelerated by the accelerator
54 is emitted to the beam transport system 59, which is referred to
as an HEBT (High Energy Beam Transport) system. The beam transport
system 59 is provided with a vacuum duct that serves as an orbit
path of the charged particle beam 1; a switching electromagnet 68,
which is a switching device for switching the orbits of the charged
particle beam 1; and a deflection electromagnet that deflects a
beam at a predetermined angle. The charged particle beam 1 that has
been sufficiently energized by the accelerator 54 and travels
through the transport path formed of the vacuum duct is led to the
irradiation apparatus provided in a designated treatment room; the
orbit of the charged particle beam 1 is changed by the switching
electromagnet 68, as may be necessary.
<Irradiation System>
[0033] The irradiation system includes the particle beam
irradiation apparatus 58 that forms the charged particle beam 1
supplied from the beam transport system 59 into an irradiation
field conforming to the size or the depth of a diseased site of a
patient as the irradiation subject 15 and that irradiates the
charged particle beam 1 onto the diseased site. In general, in the
particle beam therapy system 51, as irradiation field forming
methods, the scatterer method, the Wobbler method, and the scanning
method have been proposed. The irradiation systems (particle beam
irradiation apparatuses) have different configurations, depending
on the irradiation methods thereof. The present invention is to be
applied to a particle beam therapy system (referred to also as a
"scanning-type particle beam therapy system") utilizing the
scanning method typified by spot scanning or raster scanning. When
being a scanning-type particle beam therapy system, the particle
beam irradiation apparatus 58 is provided with a pair of scanning
electromagnets 3 for scanning the pencil-shaped charged particle
beam 1 in accordance with the shape of the irradiation subject 15
and a position monitor 7 for measuring an irradiation position and
the like. The detailed configuration of the particle beam
irradiation apparatus 58 will be described later.
<Control System>
[0034] The control system will be explained with reference to FIG.
4, which illustrates the functional block. Meanwhile, in general,
as the controller of the particle beam therapy system 51, a
workstation or a computer is utilized. Accordingly, in many cases,
the controller is referred to as a "computer". For example, the
main controller 70 in FIG. 4 is, in fact, a function of a computer,
which is, in many cases, referred to as an irradiation system
common computer; however, the main controller 70 is dealt with as a
controller having a specific function. Each of the sub-controllers
71a and 71b is a function of a computer, which is, in many cases,
referred to as an apparatus control computer; however, each of the
sub-controllers 71a and 71b is dealt with as a controller having a
specific function. The sub-controllers 71a and 71b perform control
of the whole subsystems, which consists of a part of apparatuses in
the treatment room, such as a treatment table for laying a patient
24 and an X-ray image-capturing device for radiographing the
position of a diseased site (irradiation subject 15).
[0035] An irradiation system 80 is configured with the main
controller 70, apparatuses provided in an irradiation operation
room 81, apparatuses provided in a treatment room 82a, and
apparatuses provided in a treatment room 82b. In the treatment room
82a, there is arranged an irradiation apparatus unit 31a of the
particle beam irradiation apparatus 58a. In the treatment room 82b,
there is arranged an irradiation apparatus unit 31b of the particle
beam irradiation apparatus 58b.
[0036] The "consoles" 72a, 72b, 73a, 73b, 74a, and 74b connected
with the sub-controllers 71a and 71b are each a keyboard, a
display, or the like or a terminal such as a controller box; in
other words, they are each a man-machine interface. The consoles
72a and 72b are provided in the irradiation operation room 81; the
consoles 73a and 74a are provided in the treatment room A (82a);
the consoles 73b and 74b are provided in the treatment room B
(82b). Control boards 75a and 75b are connected with the bottom
parts of the sub-controllers 71a and 71b, respectively. Each of the
control boards 75a and 75b includes, specifically, a driver, an
amplifier, a sequencer, and the like for various kinds of
apparatuses 76a, 76b, 77a, and 77b, which are control subjects. The
control board 75a allows communication of signals between the main
controller 70 and an interlock information inputting device 84a and
between the main controller 70 and the irradiation apparatus unit
31a; the control board 75b allows communication of signals between
the main controller 70 and an interlock information inputting
device 84b and between the main controller 70 and the irradiation
apparatus unit 31b. The apparatuses 76a and 77a, the interlock
information inputting device 84a, and the irradiation apparatus
unit 31a are connected with the bottom part of the sub-controllers
71a by way of the control board 75a; the apparatuses 76b and 77b,
the interlock information inputting device 84b, and the irradiation
apparatus unit 31b are connected with the bottom part of the
sub-controllers 71b by way of the control board 75b. Each of the
apparatuses 76a, 76b, 77a, and 77b is, specifically, a motor for
moving the respective axles of a treatment table, a motor for
driving an X-ray image-capturing device in the irradiation
apparatus, or the like. A scanning electromagnet power source 4
supplies respective energization currents to scanning
electromagnets 3a and 3b provided in the irradiation apparatus
units 31a and 31b, respectively, by way of a switching circuit
79.
[0037] The motor for the treatment table and the motor for the
X-ray image-capturing device are not moved when a beam is being
irradiated. That is to say, it is not required to implement control
in synchronization with the electromagnet for the accelerator and
the like controlled by the accelerator system 60. In order to
exchange information about their conditions, the main controller 70
and the sub-controller 71a or 71b communicate with each other, for
example, by use of a Ready signal that indicates in which treatment
room the irradiation apparatus unit 31a or 31b has completed its
positioning and is ready to irradiate a beam, and a signal that
indicates in which treatment room the irradiation apparatus unit
31a or 31b has irradiated a beam and completed its irradiation, and
the like. Briefly speaking, it is regarded as carrying out events
sequentially.
[0038] Here, the functions of the irradiation system common
computer (main controller 70) and the apparatus control computers
(sub-controllers 71a and 71b) will be explained. As described
above, in the treatment rooms 82a and 82b, there are provided the
irradiation apparatus units 31a and 31b of the particle beam
irradiation apparatuses 58a and 58b, respectively. Additionally, as
described above, in the case of a scanning-type particle beam
therapy system, in each of the irradiation apparatus units 31a and
31b, there are provided a pair of scanning electromagnets 3, the
position monitor 7 for measuring an irradiation position, and the
like. In this regard, however, as illustrated in FIG. 4, control of
the scanning electromagnets 3 and processing of signals from the
position monitor 7 are performed not by the apparatus control
computer but by the irradiation system common computer (an
irradiation management apparatus, described later).
[0039] The foregoing fact is based on two reasons. The first reason
is requirement for control in synchronization with the accelerator
system; the second reason is instantaneousness (requirement for
reducing wasteful time as much as possible). In order to realize
irradiation as per a treatment plan, it is required to control the
accelerator system 60 and the irradiation system 80 in such a way
that they are synchronized with each other. It is true that the
sub-controllers 71a and 71b and the main controller 70 can perform
processing at the same time and in a parallel manner, by use of a
synchronization signal or the like. However, the more apparatuses
to be passed through there are, the more wasteful time occurs and
hence control performance is deteriorated. Accordingly, in the
particle beam therapy system 51 according to the present invention,
the accelerator system 60, the scanning electromagnet 3, and the
like, which need to be controlled in real time during irradiation
of a beam, are controlled by the irradiation system common computer
(the irradiation management apparatus), which is the main
controller 70; in contrast, the treatment table, the X-ray
image-capturing device, and the like, which do not need to be
driven during irradiation of a beam, are controlled by the
apparatus control computers, which are the sub-controllers 71a and
71b.
[0040] This is because intensive management by a single main
controller 70 can reduce wasteful time as much as possible, thereby
realizing high-accuracy beam irradiation without deteriorating the
control performance. For the purpose of ensuring the
instantaneousness, as well, it is desirable that signal processing
for the interlock information inputting devices 84a and 84b and the
like, which function as the interlock (emergency-stop processing),
and the like are performed by the irradiation system common
computer (the irradiation management apparatus), which is the main
controller 70. The irradiation system common computer is provided
with a so-called "contest for accelerator" function in which it is
managed which treatment room occupies the charged particle beam
1.
[0041] Next, the particle beam irradiation apparatus 58 will be
explained with reference to FIG. 3. The particle beam irradiation
apparatus 58 is provided with the irradiation apparatus unit 31,
the scanning electromagnet power source 4, the interlock
information inputting device 84, and an irradiation management
apparatus 32 that performs control of the irradiation apparatus
unit 31 and the interlock information inputting device 84,
collection of data, and the like. The interlock information
inputting device 84 is provided with a patient sensor 78, described
later. The irradiation apparatus unit 31 is provided with a beam
transport duct 2 for transporting the charged particle beam 1
injected by the beam transport system 59; scanning electromagnets
3x and 3y that scan the charged particle beam 1 in the X direction
and the Y direction, respectively, which are directions
perpendicular to the charged particle beam 1; a position monitor 7;
a preamplifier 9 that amplifies a signal from the position monitor
7; a position monitor unit 8; a dose monitor 11; a preamplifier 13
that amplifies a signal from the dose monitor 11; a dose monitor
unit 12; a beam enlargement apparatus 16; a beam enlargement
control apparatus 17; a bellows 18; a vacuum duct 19; a ripple
filter 20; a range shifter 21; and a range shifter unit 23. As
illustrated in FIG. 3, the incident direction of the charged
particle beam 1 is the Z direction.
[0042] The scanning electromagnet 3x is an X-direction scanning
electromagnet that scans the charged particle beam 1 in the X
direction; the scanning electromagnet 3y is a Y-direction scanning
electromagnet that scans the charged particle beam 1 in the Y
direction. The position monitor 7 detects the size of the charged
particle beam 1, which has been deflected by the scanning
electromagnets 3x and 3y, and the passing position (the gravity
center position) through which the charged particle beam 1 passes.
The preamplifier 9 amplifies analogue data on the passing position
and the beam size detected by the position monitor 7. Here, the
beam size denotes an area, in the XY plane perpendicular to the Z
direction, through which the charged particle beam 1 passes. The
position monitor unit 8 receives the passing position and the beam
size detected by the position monitor 7, through the preamplifier
9; then, the position monitor unit 8 converts the passing position
and the beam size into digital data so as to create measured
position coordinates Ps and a measured beam size Ss.
[0043] The dose monitor 11 detects the dose of the charged particle
beam 1. The preamplifier 13 amplifies analogue data on the dose
detected by the dose monitor 11. The dose monitor unit 12 receives
the dose detected by the dose monitor 11, through the preamplifier
13; then, the dose monitor unit 12 converts the dose into digital
data so as to create a measured dose Ds.
[0044] The beam enlargement apparatus 16 enlarges the beam size of
the charged particle beam 1, as may be necessary. The vacuum duct
19 ensures a vacuum region through which the charged particle beam
1 passes. The bellows 18 connects the beam transport duct 2 with
the vacuum duct 19 in an expandable/contractible manner and extends
the vacuum region toward the irradiation subject 15. The ripple
filter 20 is also referred to as a ridge filter and formed in a
convex shape. The ripple filter 20 causes an energy loss to the
charged particle beam 1, which is a monochromatic beam having
approximately single energy and transported from the accelerator
54, so that the energy has a range.
[0045] The depth-direction (Z direction) position coordinates of
the irradiation subject 15 is controlled by varying the energy of
the charged particle beam 1 through change in the acceleration
energy of the accelerator 54 and by varying the energy of the
charged particle beam 1 through the range shifter 21. The range
shifter 21 adjusts the range of the charged particle beam 1 little
by little. Considerable change of the range of the charged particle
beam 1 is performed by changing the acceleration energy of the
accelerator 54, and slight change of the range of the charged
particle beam 1 is performed by changing the setting of the range
shifter 21.
[0046] The irradiation management apparatus 32 reads the treatment
plan data pieces F0 generated by the treatment planning apparatus;
then, in order to control the irradiation dose, the irradiation
management apparatus 32 creates setting data Fi by rearranging the
treatment plan data pieces in order of irradiation onto irradiation
spots, which are divided irradiation units. In other words, the
setting data Fi is sequentialized treatment plan data (sequential
data, described later). Based on the setting data Fi, the
irradiation management apparatus 32 outputs the setting data pieces
Fo, which are respective commands to the apparatuses.
[0047] The elements of the setting data Fi are desired irradiation
position coordinates Pi, a desired dose Di, a desired beam size Si,
a desired accelerator setting Bi, and a range shifter insertion
amount Ri; respective elements of the setting data Fi are data
items obtained by sequentializing a desired irradiation position
coordinates PiO, a desired dose Di0, a desired beam size Sio, a
desired accelerator setting Bi0, and a range shifter insertion
amount Ri0, which are the elements of the treatment plan data F0.
The setting data Fo includes an accelerator setting command Bo, a
range shifter command Ro, a command current Io (an uncorrected
command current), a command current Ir (a command current obtained
by correcting the command current Io), a beam size command So, and
a desired dose Do.
[0048] The irradiation management apparatus 32 receives irradiation
records such as the measured position coordinates Ps, the measured
dose Ds, and the measured beam size Ss in preliminary irradiation
performed when the patient 24 does not exist, and evaluates the
irradiation records. The irradiation management apparatus 32
creates the command current Ir by correcting the command current
Io, based on the measured position coordinates Ps, and transmits
the command current Io or the command current Ir to the scanning
electromagnet power source 4. The irradiation management apparatus
32 receives irradiation records, such as the measured position
coordinates Ps, the measured dose Ds, and the measured beam size Ss
in actual irradiation where irradiation onto the patient 24 is
actually performed, and stores the irradiation records in the
actual irradiation in the patient file server.
[0049] The irradiation management apparatus 32 outputs a trigger
signal, a count start signal, a beam supply command, and a beam
stop command, and controls the irradiation spot and the irradiation
dose at the irradiation subject 15. The irradiation spots are
layers divided in the Z direction; each irradiation spot is divided
into a slice, which corresponds to the kinetic energy of the
charged particle beam 1, and the XY direction at each slice. In
this embodiment, there will be explained an irradiation method in
which the charged particle beam 1 is stopped when slices are
changed, and the charged particle beam 1 is continuously irradiated
when irradiation is performed within a single and the same slice.
The irradiation management apparatus 32 scans the charged particle
beam 1 onto respective slices, of the irradiation subject 15, that
are layers corresponding to kinetic energy levels. The irradiation
management apparatus 32 changes setting of each apparatus for each
irradiation spot in response to the trigger signal, and starts to
measure the irradiation dose of an irradiation spot in response to
the count start signal; when the measured dose Ds reaches the
desired dose Do, the irradiation management apparatus 32 performs
control for the next irradiation spot; when respective irradiations
onto irradiation divisions (slices) obtained by dividing the
irradiation subject 15 are completed, the irradiation management
apparatus 32 outputs the beam stop command to the accelerator
system 60 so as to stop the charged particle beam 1. Next, the
irradiation management apparatus 32 outputs the trigger signal and
sequentially changes the corrected command current Ir, the beam
size command So, the accelerator setting command Bo, and the range
shifter command Ro; then, the irradiation management apparatus 32
performs irradiation of the charged particle beam 1 until
irradiation onto all the slices of the irradiation subject 15 is
completed.
[0050] The scanning electromagnet power source 4 changes the
setting currents for the scanning electromagnets 3x and 3y, based
on the command current Io (Ir), which is outputted from the
irradiation management apparatus 32 and is a control input to the
scanning electromagnet 3. The beam enlargement control apparatus 17
outputs to the beam enlargement apparatus 16 the beam size command
So for setting the beam size at the position monitor 7. The range
shifter unit 23 outputs to the range shifter 21 the range shifter
command Ro for changing the energy of the charged particle beam
1.
[0051] The patient sensor 78 detects the motion of the patient 24
and outputs a patient signal on which the motion of the patient 24
is reflected. The patient sensor 78 is to stop irradiation when the
motion of the patient exceeds a predetermined range, i.e., to
perform emergency-stop processing for the particle beam therapy
system. As the patient sensor 78, the following devices may be
utilized. Specifically, there are conceivable a method of detecting
the flow of expired air by means of a flow sensor, a method of
measuring the temperature change, due to inspiration, in the
vicinity of nasal cavities through image processing by a thermistor
or an infra-red camera, a method of detecting the abdominal
movement of a patient by means of a position sensitive detector
(position sensor) that senses a laser-beam source mounted on the
abdomen, and a method of converting the abdominal movement of a
patient into a signal by means of a laser displacement gauge.
Additionally, the patient sensor 78 may be utilized also as the
respiratory sensor that is utilized for respiration-synchronized
irradiation of the particle beam therapy system 51. This is because
both the respiratory sensor and the patient sensor are utilized for
the purpose of detecting the motion of the patient 24.
[0052] Next, the technology disclosed in Patent Document 1, which
is a basis of the present invention, will briefly be explained. The
invention disclosed in Patent Document 1 has been implemented for
the particle beam therapy system 51 that irradiates the charged
particle beam 1, accelerated by the accelerator 54 and scanned by
the scanning electromagnet 3, onto the irradiation subject 15; the
particle beam therapy system has the following characteristics:
[0053] (A) There is provided the irradiation management apparatus
32 that controls the scanning electromagnet 3, based on the desired
irradiation position coordinates Pi of the charged particle beam
1;
[0054] (B) There is provided a position monitor 7 that measures the
measured position coordinates Ps of the charged particle beam 1;
and
[0055] (C) The irradiation management apparatus 32 is provided with
a command value generator that outputs the control input Io (Ir) to
the scanning electromagnet 3, based on the desired irradiation
position coordinates Pi and the correction data la generated on the
basis of the measured position coordinates Ps, measured by the
position monitor 7 in the preliminary irradiation in which the
excitation pattern of the scanning electromagnet 3 is the same as
that of the actual irradiation plan, and the desired irradiation
position coordinates Pi.
[0056] The method of creating the current correction data Ia will
be explained. FIG. 5 is a graph for explaining a method of
correcting a command current. There is measured the BL product vs.
the current I, which is outputted to the scanning electromagnet 3
in response to the command current Io applied to the scanning
electromagnet power source 4. The BL product is multiplication
product of the intensity B of the magnetic field and the effective
length L of the magnetic pole of the scanning electromagnet 3.
There is drawn a maximum hysteresis curve .alpha. that passed
through the saturated magnetic flux density. By averaging the one
portion of the maximum hysteresis curve .alpha., which is drawn in
such a way that the current increase, and the other portion of the
maximum hysteresis curve .alpha., which is drawn in such a way that
the current decreases, the center line .beta. of the hysteresis
loop is obtained.
[0057] The current value I(id) set through the command current Io
is determined by the desired irradiation position coordinates Pi,
at which irradiation is performed, the center line .beta. of the
hysteresis loop, the energy of the charged particle beam 1, and the
distance between the position at which the scanning electromagnet 3
is disposed and the irradiation position. While considering the
Lorentz force exerted on the charged particle beam 1, the value of
the BL product can be obtained from the position coordinates of the
charged particle beam 1. The command current Io is a command value
that corresponds to the current I(id) at the intersection point P'
(not represented) of the value BL(id) of the ideal BL product
calculated from the desired irradiation position coordinates Pi
with the center line .beta. of the hysteresis loop. BL(id) is the
expected value BL(ex) of the value of the BL product to be
measured.
[0058] A value BL(me) of the BL product is calculated from the
measured position coordinates Ps. The point P in FIG. 5 is the
actually measured value. There will be considered a case where the
value BL(me) of the measured BL product is displaced by ABL from
the expected value BL(ex). In order to correct the current, the
displacement by ABL is made by use of a straight line having a
gradient K, which is a tangential line at the intersection point P'
at which the command current Io is obtained. In order to make a
correction, there is obtained the current value I1 at which the BL
product becomes BL(ex). After the current value I1 is obtained,
there can be generated the command current Ir for setting the
current value to the current value I1 corresponding to BL(id). In
such a way as described above, the displacement of the charged
particle beam 1 due to the hysteresis of the scanning electromagnet
3 can be made to fall within a tolerance range.
[0059] The straight line (dashed line) .gamma. is a line having the
gradient K that is the same as the gradient of the tangential line,
at the current value I(id), of the center line .beta.. The gradient
K can be expressed by the equation (1), and the corrected current
value I1 can be expressed by the equation (2).
K = BL I ( id ) ( 1 ) I 1 = I ( id ) - .DELTA. BL K ( 2 )
##EQU00001##
where .DELTA.BL=BL(me)-BL(ex). The correction current value
.DELTA.I to be set through the current correction data Ia is
.DELTA.BL/K.
[0060] Next, there will be considered a case where emergency-stop
processing for the particle beam therapy system 51 is performed. As
described above, the emergency-stop processing is processing of
interrupting irradiation when a contingency occurs. The situation
where the emergency-stop processing should be performed is, for
example, a case where the measured position coordinates Ps or the
measured beam size Ss, of the charged particle beam 1, detected by
the position monitor 7 exceeds an allowable value, or a case where
there occurs such a contingency as the patient 24 becomes ill, or
the like. FIG. 3 illustrates a case where the particle beam
irradiation apparatus 58 according to Embodiment 1 is provided with
the patient sensor 78 that detects the motion of a patient;
however, there are provided therein a patient call button
(unillustrated) for the patient 24 to inform that the patient 24
himself or herself has become ill and an irradiation stop button
(unillustrated) that enables a doctor or an engineer or the like to
stop irradiation in the event of an emergency. Each of the patient
sensor 78, the patient call button, the irradiation stop button,
and the position monitor 7 works as the interlock information
inputting device 84 that generates an interlock signal that
activates the interlock function for stopping beam irradiation in
the event of an contingency so as to ensure the safety. The
interlock information inputting device 84 includes a signal
generator that generates the interlock signal from a signal
outputted by the patient sensor 78, the patient call button, the
irradiation stop button, or the position monitor 7.
[0061] As described above, in the interlock processing
(emergency-stop processing), instantaneousness is required; thus,
it is desirable that this signal processing is performed by the
irradiation system common computer (irradiation management
apparatus 32), which is the main controller 70. The irradiation
management apparatus 32, which is the main controller 70, according
to Embodiment 1 of the present invention has the following
characteristics.
[0062] The irradiation management apparatus 32 determines that
irradiation should be stopped, when the motion of the patient 24
exceeds a predetermined range, from a signal (the patient signal)
detected by the patient sensor 78. The irradiation management
apparatus 32 determines that irradiation should be stopped, when
the measured position coordinates Ps or the measured beam size Ss
of the charged particle beam 1, detected by the position monitor 7,
exceeds a predetermined range (an allowable value) (corresponding
to a case where the quality of the charged particle beam 1 is
deteriorated). The irradiation management apparatus 32 determines
that irradiation should be stopped also in the event of an
emergency where by operating the patient call button, the patient
24 informs that he has become ill, or an emergency where by
operating the irradiation stop button, a doctor or an engineer or
the like expresses his or her will to stop irradiation. The
irradiation management apparatus 32, which is the main controller
70, controls also the accelerator system 60 (the accelerator 54,
the beam transport system 59); therefore, when determining that
irradiation should be stopped, the irradiation management apparatus
32 can stop the irradiation of the charged particle beam 1, by
controlling the accelerator system 60. The predetermined range for
the motion of the patient 24 detected by the patient sensor 78 is a
range obtained by adding a margin to the detection value
corresponding to the moving range of the patient 24 at a time when
the patient 24 normally respires. There will be described later the
method in which the motion of the patient 24 is detected and then
it is determined whether or not the motion has exceeded the
predetermined range.
[0063] The irradiation management apparatus 32 according to
Embodiment 1 is further provided with the following
characteristics. As described above, the irradiation management
apparatus 32 includes a command value generator that outputs
correction data Ia generated based on preliminary irradiation and a
control input for the scanning electromagnet 3. That is to say, the
irradiation management apparatus 32 includes a control input, as
sequential data, preliminarily corrected by the command value
generator. The sequential data denotes such data as is implemented
step by step (every discrete processing that is implemented in a
predetermined time). Because the desired irradiation position
coordinates Pi is given as sequential data, there is required, also
as sequential data, the control input, for the scanning
electromagnet 3, that corresponds to the desired irradiation
position coordinates Pi. Base on the interlock signal generated by
the interlock information inputting device, the irradiation
management apparatus 32 performs the foregoing determination on
irradiation stop; when the irradiation is stopped, the irradiation
management apparatus 32 stores the step (stop step) corresponding
to that desired irradiation position coordinates Pi (i.e., stop
position coordinates) in a stop step storage memory, which is
incorporated therein. For example, there is stored the number "n"
of a step in which there is outputted a control input corresponding
to the desired irradiation position coordinates Pi in a given slice
(stop step storage procedure). The stop step storage memory may be
provided not only in the irradiation management apparatus 32 but
also outside the irradiation management apparatus 32.
[0064] The irradiation management apparatus 32 according to
Embodiment 1 of the present invention is further provided with the
following characteristics. In particle beam therapy, a single
therapy time is approximately 30 minutes; out of the 30 minutes,
several minutes are for irradiation. It cannot necessarily be said
that during the particle beam therapy, there occurs no contingency
such as the patient 24 becoming ill, the patient 24 having a
coughing fit, or the quality of the charged particle beam 1 being
deteriorated. The case where the measured position coordinates Ps
or the measured beam size Ss of the charged particle beam 1,
detected by the position monitor 7, exceeds a predetermined range
(an allowable value) corresponds to a case where the quality of the
charged particle beam 1 is deteriorated. In this case, irradiation
is stopped through sensing by a sensor or by operating a button or
the like so that the therapy is interrupted. In the case where the
foregoing contingency is cancelled and irradiation is resumed, the
irradiation management apparatus 32 controls the scanning
electromagnet 3 with a beam unirradiated, for example, from the
initial step for a given slice (idle operation procedure). Control
of the scanning electromagnet 3 with a beam unirradiated will be
referred to herein as "idle operation". The step where the idle
operation is started will be referred to as a start step.
[0065] This is for the following reason. When irradiation is
resumed simply from an irradiation position at which the
irradiation has been interrupted, control of the scanning
electromagnet 3 is performed halfway through the excitation
pattern; however, when the scanning electromagnet 3 is controlled
from the initial step for a given slice, the control can be
performed with the same excitation pattern as the preliminary
irradiation has been performed. It goes without saying that when a
beam is irradiated at this timing, double irradiation is caused;
thus, it is significant to perform the idle operation. Accordingly,
correction based on the preliminary irradiation becomes effective,
and high-accuracy beam irradiation can be performed at the same
level as when there exists no interruption.
[0066] In view of the reproducibility, it is desirable to perform
the idle operation from the initial step for a given slice;
however, it is empirically known that even when the idle operation
is performed from a step that is predetermined steps (predetermined
spots) prior to the step corresponding to the stop position, a
considerable effect can be obtained. Thus, in Embodiment 1, as the
start step, there is selected the initial step for a given slice,
or is selected the step that is prior to the step corresponding to
the stop position by predetermined steps which are preliminarily
set. That is to say, the operator such as a doctor or an engineer
can make selection between idle operation to be performed from the
initial step for a given slice and idle operation to be performed
from a step that is prior to the step corresponding to the stop
position by predetermined steps which are preliminarily set.
[0067] Here, there will be explained the method of making decision
on how many the predetermined steps should be. The effective number
of steps for the idle operation depends mainly on the scale or the
performance of the scanning electromagnet 3. Thus, it is desirable
that an interrupted situation is actually and intentionally
reproduced, experiments are carried out with a different number of
steps, and after the confirming the effect, the number of steps is
decided. In some cases, the idle operation is performed from
halfway through the immediately previous slice. It is allowed that,
as described above, the idle operation is performed from a step
that is prior to the initial step for a given slice.
[0068] Lastly, it is required that the irradiation management
apparatus 32 controls the particle beam irradiation apparatus 58 in
such a way that there is irradiated the portion onto which a beam
has not been irradiated due to interruption. Therefore, the
irradiation management apparatus 32 controls the accelerator system
60 (the accelerator 54, the beam transport system 59) in such a way
that after idle operation is carried out up to a step corresponding
to the stop position, beam irradiation is started from the
resumption step that follows the stop step, so that the remaining
steps can be performed (irradiation start procedure). In the case
of an irradiation method in which the charged particle beam 1 is
stopped when slices are changed and the charged particle beam 1 is
continuously irradiated when irradiation is performed within a
single and the same slice, sequential time management (step
management) enables the irradiation position and the irradiation
dose at the irradiation position to be reproduced. That is to say,
even in the case where the irradiation dose at an irradiation spot,
which is a stop position where irradiation has been interrupted,
has not reached the desired dose Do, irradiation is resumed with a
halfway irradiation dose, and after the irradiation dose at the
irradiation spot reaches the desired dose Do, irradiation can move
to the next irradiation spot.
[0069] The characteristics of the irradiation management apparatus
32 have been explained; the flow of the emergency-stop processing
by the particle beam therapy system 51 will be summarized by use of
FIG. 6. FIG. 6 is a flowchart representing a procedure for stopping
and resuming beam irradiation in a particle beam therapy system
according to Embodiment 1. In the case where during the particle
beam therapy, there occurs a contingency such as the patient 24
becoming ill, the patient 24 having a coughing fit, or the quality
of the charged particle beam 1 being deteriorated, the irradiation
management apparatus 32 performs the foregoing determination on
irradiation stop, based on the interlock signal generated by the
interlock information inputting device, and stops the irradiation.
When the irradiation is stopped, the irradiation management
apparatus 32 stores the step corresponding to that desired
irradiation position coordinates Pi (i.e., stop position
coordinates). For example, there is stored the number "n" of a step
in which there is outputted a control input corresponding to the
desired irradiation position coordinates Pi in a given slice (the
step S1: the stop step storage procedure). In the case where the
foregoing contingency is cancelled and irradiation is resumed, the
irradiation management apparatus 32 activates the scanning
electromagnet power source 4, with a beam unirradiated in the
process from a predetermined start step to the stop step, so as to
perform only magnetic-field excitation of the scanning
electromagnet 3 (the step S2: the idle operation procedure). After
the idle operation is carried out up to a step corresponding to the
stop position, the irradiation management apparatus 32 controls the
accelerator system 60 (the accelerator 54, the beam transport
system 59) from the resumption step that follows the stop step so
as to resume beam irradiation (the step S3, the irradiation start
procedure).
[0070] As a result, in the particle beam therapy system 51
according to Embodiment 1, even in the case where a contingency
such as a patient becoming ill occurs, irradiation can be
interrupted by operating a sensor or a button or the like, and the
scanning electromagnet 3 is controlled, with a beam unirradiated,
from the initial step for a given slice or from a step that is
predetermined steps before (start step); thus, the excitation
pattern for the scanning electromagnet 3 is made the same as that
at a time when preliminary irradiation is performed, correction
based on the preliminary irradiation (i.e., information from the
preliminary irradiation) can be made effective, and hence
high-accuracy beam irradiation can be realized. Accordingly, even
in the case where the emergency-stop processing is performed during
therapy, the effect of the hysteresis of the scanning electromagnet
3 can be eliminated and high-accuracy beam irradiation can be
resumed from an irradiation position where irradiation has been
interrupted.
[0071] There will be explained the method in which the motion of
the patient 24 is detected and then it is determined whether or not
the motion has exceeded a predetermined range. A change caused by
normal respiration is measured, as a respiratory signal, through
the foregoing patient sensor 78 so that there is preliminarily
obtained a reference patient status waveform, which is a
temporally-changing waveform of a respiratory signal as a reference
(reference respiratory signal). A real patient status waveform,
generated from a respiratory signal (real respiratory signal) that
is measured by the patient sensor 78 during actual irradiation, is
compared with a reference patient status waveform, and it is
determined whether or not the difference between the real patient
status waveform and the reference patient status waveform has
exceeded a predetermined range. As the patient sensor 78 for
measuring the reference respiratory signal, there is utilized a
patient sensor of a type the same (the same measurement principle)
as that of the patient sensor 78 for measuring the respiratory
signal during therapy.
[0072] Although not a complete trigonometric function, the
reference respiratory signal is a signal of an approximately
constant cycle; therefore, there is considered a method in which by
converting the reference respiratory signal into a trigonometric
function that is closest thereto, the gain (the amplitude of the
trigonometric function) and the phase are calculated. Fourier
series expansion is applied to the reference respiratory signal
R.sub.tj(t), for example, as represented in the equation (3); as
represented in the equation (4), among the expanded 0th-order term
through nth-order term, a pair of coefficients a.sub.1 and b.sub.1,
of the trigonometric function, which correspond to the 1st-order
term of the equation (3) are calculated; then, the calculated
coefficients a.sub.1 and b.sub.1 are specified as the describing
functions that indicate the state of the respiratory signal. In
other words, there are calculated the coefficients a.sub.1 and
b.sub.1 of the cosine function and the sine function that configure
the fundamental waveform component that is obtained by removing the
constant term and the high-frequency components from the reference
respiratory signal. FIG. 7A represents the waveform of a describing
function formed of a.sub.1 and b.sub.1 obtained from the reference
respiratory signal NW and the equation (2).
R ( t ) = a 0 2 + n = 1 .infin. ( a n cos ( n .omega. res t ) + b n
sin ( n .omega. res t ) ) ( 3 ) a 1 = 1 .pi. .intg. 0 2 .pi. R ( t
) cos ( .omega. res t ) .omega. res t b 1 = 1 .pi. .intg. 0 2 .pi.
R ( t ) sin ( .omega. res t ) .omega. res t } ( 4 )
##EQU00002##
[0073] As represented in the equations (5) and (6), the gain
G.sub.res and the phase .phi..sub.res can be obtained respectively
from a.sub.1 and b.sub.1 that form the describing function
extracted as described above.
G res = a 1 2 + b 1 2 ( 5 ) .phi. res = arctan b 1 a 1 ( 6 )
##EQU00003##
[0074] FIG. 7A and FIG. 7B are charts representing a reference
respiratory signal and a real respiratory signal respectively. FIG.
7A is a chart representing a reference respiratory signal; FIG. 7B
is a chart representing a real respiratory signal. The abscissa
denotes the time; the ordinate denotes the signal value of the
respiratory signal R(t). The cycle of the reference respiratory
signal NW is T.sub.res; the cycle of the real respiratory signal
R.sub.rl(t) is T.sub.res1. Reference character BL in FIG. 7A and
FIG. 7B denotes the base line of each of the reference respiratory
signal NW and the real respiratory signal R.sub.rl(t). The real
respiratory signal R.sub.rl(t) is irregular signal. However, for
example, when respiratory induction is performed based on the sine
wave signal on the basis of the cycle T.sub.res of the reference
respiratory signal NW or the reference respiratory signal
R.sub.tj(t), the real respiratory signal R.sub.rl(t) also becomes a
cyclic function having a cycle the same as that of the reference
respiratory signal R.sub.rl(t). By utilizing the respiratory
characteristics thereof, as is the case with the reference
respiratory signal R.sub.tj(t), also with regard to the real
respiratory signal R.sub.rl(t), there can be calculated a
describing function including the pair of coefficients a.sub.1 and
b.sub.1, of the trigonometric functions, that correspond to the
1st-order terms when Fourier series expansion is applied, as
represented in the equation (4).
[0075] In the case where the motion of the patient 24 is detected
and then it is determined whether or not the motion has exceeded a
predetermined range, it is only necessary that the cycle T.sub.res1
of the real respiratory signal R.sub.rl(t) approximately coincides
with the cycle T.sub.res of the reference respiratory signal
R.sub.tj(t). By setting predetermined ranges for the gain G.sub.res
and the phase .phi..sub.res, the ranges of the gain G.sub.res and
the phase .phi..sub.res can be adopted as predetermined ranges. For
example, when a patient has a coughing fit, the gain and the phase
of the real respiratory signal rapidly change; thus, the gain
G.sub.res and the phase .phi..sub.res exceed the predetermined
ranges, whereby the motion of the patient caused by the coughing
fit can be detected. In addition, when the patient falls into a
sleep, the gain of the real respiratory signal gradually becomes
small, and the phase of the real respiratory signal gradually loses
the correlation with the phase of the reference respiratory signal.
Even in this case, by setting appropriate ranges for the gain
G.sub.res and the phase .phi..sub.res, there can be detected a fact
that the patient has fallen into a sleep or a sign that the patient
is going to fall into a sleep.
[0076] As described above, in the particle beam therapy system
according to Embodiment 1, there are provided the irradiation
management apparatus 32 that controls the scanning electromagnet 3,
based on the desired irradiation position coordinates Pi of the
charged particle beam 1; the position monitor 7 that measures the
measured position coordinates Ps of the charged particle beam 1;
and the interlock information inputting device 84 that generates an
interlock signal for stopping irradiation of the charged particle
beam 1, when a contingency occurs. The irradiation management
apparatus 32 is provided with a command value generator that
outputs the control input Io (Ir) to the scanning electromagnet 3,
based on the desired irradiation position coordinates Pi and the
correction data Ia generated on the basis of the measured position
coordinates Ps, measured by the position monitor 7 in the
preliminary irradiation in which the excitation pattern of the
scanning electromagnet 3 is the same as that of the actual
irradiation plan, and the desired irradiation position coordinates
Pi; and a stop step storage memory that stores a stop step
corresponding to the desired irradiation position coordinates Pi at
which irradiation of the charged particle beam 1 stops, when the
interlock signal is generated by the interlock information
inputting device 84. When irradiation of the charged particle beam
1 is resumed, the irradiation management apparatus 32 performs idle
operation in which the scanning electromagnet 3 is controlled, with
the charged particle beam 1 unirradiated, from a start step, which
is situated prior to the stop step and is different from the
initial step corresponding to the initial desired irradiation
position coordinates in actual irradiation, to the stop step, and
then the irradiation management apparatus 32 irradiates the charged
particle beam 1 from the desired irradiation position coordinates
Pi corresponding to the stop step; therefore, in the case where
emergency-stop processing is performed during therapy, idle
operation is carried out, based on irradiation command data
including a control input to the scanning electromagnet 3, from a
start step, which is situated prior to the stop step and is
different from the initial step, and beam irradiation is started
from an irradiation position where the irradiation has been
interrupted. As a result, the effect of the hysteresis of the
scanning electromagnet 3 is eliminated, so that high-accuracy beam
irradiation can be resumed from the irradiation position where the
irradiation has been interrupted.
Embodiment 2
[0077] In Embodiment 1, there has been described idle operation of
the scanning electromagnet 3 at a time when irradiation is resumed
after therapy has been interrupted; however, in Embodiment 2, there
will be described a method of initializing the scanning
electromagnet 3 before the idle operation thereof.
[0078] FIG. 8 is a schematic diagram representing a fact that a
diseases site is scanned with a beam along a beam path in a
particle beam therapy system according to Embodiment 2 of the
present invention. The charged particle beam 1 scanned by the
scanning electromagnet 3 is irradiated onto each of the layers
(slices) of a diseased site such as a cancer, which is the
irradiation subject 15, along an irradiation path 14 (referred to
also as a beam path). In the scanning-type particle beam therapy
system 51, the beam path 14 for each layer is generated by use of a
treatment planning apparatus. In the treatment planning apparatus,
an optimum treatment plan is generated in such a way that the
cancer diseased site is reached through as short path as possible
and there exists no unnecessary irradiation onto normal tissues. In
the treatment planning apparatus, there is incorporated a computer
that performs the optimization; the optimum path is obtained by use
of the computer. A doctor, who is a main person (person in charge)
for the therapy, eventually determines whether or not the obtained
path is optimum. The X-direction scanning electromagnet 3x and the
Y-direction scanning electromagnet 3y are controlled by the
irradiation management apparatus 32 in such a way that the charged
particle beam 1 is scanned along the generated beam path 14, and
the scanning electromagnet power source 4 (referred to also as a
pattern power source) supplies a driving current (command
current).
[0079] FIG. 9A and FIG. 9B are charts representing the hysteresis
characteristics of a scanning electromagnet in a particle beam
therapy system according to Embodiment 2. FIG. 9A represents the
hysteresis characteristics of the X-direction scanning
electromagnet 3x; FIG. 9B represents the hysteresis characteristics
of the Y-direction scanning electromagnet 3y. As represented in
FIG. 9A and FIG. 9B, the magnetic material, which is a material of
the scanning electromagnet, has hysteresis characteristics. In FIG.
9 A and FIG. 9B, the abscissa denotes the magnetic-field intensity
H of a magnetic field generated by an inputted command current; the
ordinate denotes the magnetic flux density B. ".alpha.x" denotes a
maximum hysteresis curve of the X-direction scanning electromagnet
3x; ".alpha.y" denotes a maximum hysteresis curve of the
Y-direction scanning electromagnet 3y. The hysteresis
characteristics denote the relationship between the magnetic-field
intensity H and the magnetic flux density B in which even when the
magnetic-field intensity H is determined, the magnetic flux density
B is not uniquely determined simply based on the magnetic-field
intensity H, as showed in FIG. 9 A and FIG. 9B. In order to realize
the beam path 14 optimized for each diseased site, the scanning
electromagnet 3 is excited in accordance with each of patterns that
vary depending on diseased sites. Accordingly, the BH hysteresis
curves on the BH plane, along which the magnetization
characteristics of the scanning electromagnet 3 follow, vary
depending on the beam paths.
[0080] For example, in the case where the scanning electromagnet 3
is excited in a given pattern, the magnetic characteristic of the
scanning electromagnet 3 follows the BH hysteresis curves such as
thin solid lines 26a and 27a in FIG. 9A and FIG. 9B. Because the
particle beam therapy system 51 deals with a human body, the
irradiation is stopped when a contingency occurs. The coordinates
of a point, on the hysteresis curve, that corresponds to the stop
position (stop spot) where the irradiation has been stopped are
(P1x, P1y). After that, the irradiation is resumed after the safety
is confirmed. When the irradiation is resumed, it is required to
resume the irradiation after the condition of the scanning
electromagnet 3 at a time when irradiation has not been stopped is
reproduced. In order to reproduce the condition of the scanning
electromagnet 3, it is required to reproduce the same magnetic flux
density B, the same magnetic-field intensity H, and the same
magnetic-field vs. time gradient dH/dt. Accordingly, it is
effective that before the irradiation of the charged particle beam
1 is started, the scanning electromagnet 3 is initialized, for
example, as B=0, H=0, and dH/dt=0, in such a way that the
irradiation is always started with the same condition of the
scanning electromagnet 3, i.e., in such a way that when the
condition of the scanning electromagnet 3 is represented on the BH
plane, the BH hysteresis curve always starts from the same point
(P1x, P1y). The broken lines 26b and 27b are the BH hysteresis
curves at a time when the scanning electromagnet 3 is controlled
with irradiation unstopped. The initialization of the scanning
electromagnet 3 and the idle operation explained in Embodiment 1
enable the condition of the scanning electromagnet 3 to always
start from the same point (P1x, P1y) when represented on the BH
plane.
[0081] With regard to the initialization of the scanning
electromagnet 3, there is given a predetermined excitation pattern,
for example, in such a way that the scanning electromagnet 3 is
excited up to +H-direction maximum value, which is within the
specification range, and then is excited up to -H-direction maximum
value, which is within the specification range. By, as described
above, exciting the scanning electromagnet 3 up to the maximum
values, it can be expected that the residual magnetism in the
magnetic material of the scanning electromagnet 3 is eliminated.
The initialization of the scanning electromagnet 3 is not limited
to the condition in which B=0, H=0, and dH/dt=0; there may exist an
offset, as long as the reproducibility can be ensured.
[0082] In Embodiment 1, there has been explained an example in
which irradiation of the scanning electromagnet 3 is not performed
before idle operation. In Embodiment 1, although it is rare, a case
may occur in which even during idle operation, the effect of the
hysteresis of the scanning electromagnet 3 cannot sufficiently be
eliminated. In the case where the effect of the hysteresis of the
scanning electromagnet 3 is not sufficiently eliminated, the
positional accuracy of beam irradiation may be deteriorated to some
extent. However, in Embodiment 2, the scanning electromagnet 3 is
initialized before idle operation; therefore, the effect of the
hysteresis of the scanning electromagnet 3 can sufficiently be
eliminated.
[0083] In addition, it is also conceivable that as the method of
adjusting the condition of the scanning electromagnet 3, an
auxiliary coil is utilized. In the case where the command value for
the scanning electromagnet 3 is "0", i.e., in the case where
because no driving current is supplied from the scanning
electromagnet power source 4, the scanning electromagnet 3 is not
excited, the magnetic flux density B should be "0". However, as
represented in FIG. 9A and FIG. 9B, in some cases, due to the
hysteresis characteristics, the magnetic flux density B does not
become "0". In this situation, an electric current is applied to an
auxiliary coil provided in the scanning electromagnet 3 so that the
condition thereof is controlled, whereby the magnetic flux density
B can be made to be "0" in such a way that the residual magnetism
is cancelled. Also in such a manner as described above, beam
irradiation can be started with the condition of the scanning
electromagnet 3 made always the same (for example, the origin on
the BH plane or the stop position (P1x, P1y) in FIG. 9A and FIG.
9B). As described above, the initialization of the scanning
electromagnet 3 is not limited to the condition in which B=0; there
may exist an offset, as long as the reproducibility can be
ensured.
[0084] A procedure for stopping and resuming beam irradiation will
be explained with reference to FIG. 10. FIG. 10 is a flowchart
representing a procedure for stopping and resuming beam irradiation
in a particle beam therapy system according to Embodiment 2. The
procedure for stopping and resuming beam irradiation according to
Embodiment 2 differs from the procedure for stopping and resuming
beam irradiation according to Embodiment 1 in that a procedure (the
step S10) for initializing the scanning electromagnet 3 is added,
and the idle operation where the scanning electromagnet 3 is
controlled starts from the initial step in actual irradiation,
i.e., from the initial step in the first slice (the step S11: the
idle operation procedure).
[0085] In the case where a contingency occurs during therapy, the
irradiation management apparatus 32 performs the foregoing
determination on irradiation stop, based on the interlock signal
generated by the interlock information inputting device, and stops
the irradiation. The irradiation management apparatus 32 stores the
interruption step (the step S1: the stop step storage procedure).
The irradiation management apparatus 32 initializes the scanning
electromagnet 3 (the step S10: the magnetic-field initialization
procedure). The foregoing method can be utilized for initializing
the scanning electromagnet 3. After the magnetic-field
initialization, the irradiation management apparatus 32 activates
the scanning electromagnet power source 4, with a beam unirradiated
in the process from the initial step in actual irradiation to the
stop step, so as to perform only magnetic-field excitation of the
scanning electromagnet 3 (the step S11: the idle operation
procedure). As is the case with Embodiment 1, beam irradiation is
resumed (the step S3: irradiation start procedure).
[0086] By performing idle operation after magnetic-field
initialization, the irradiation resumption condition (i.e., the BH
hysteresis curve on the BH plane) where B=B.sub.0, H=H.sub.0, and
dH/dt=H'.sub.0 can be reproduced. In this regard, however, B.sub.0
denotes the magnetic flux density at a time before irradiation
interruption; H.sub.0 denotes the magnetic-field intensity at a
time before irradiation interruption; H'.sub.0 denotes the
magnetic-field vs. time gradient at a time before irradiation
interruption.
[0087] As the effect of adopting this sequence, even when
irradiation is interrupted halfway, the irradiation can be resumed
with the same condition, of the scanning electromagnet 3, that has
followed the same BH hysteresis curve; thus, it is made possible to
minimize the positional deviation of the irradiation spot. In
Embodiment 2, as examples of methods for reproducing the condition,
at a time before irradiation interruption, where B=B.sub.0,
H=H.sub.0, dH/dt=H'.sub.0, there have been described a method where
excitation is carried out up to the maximum level and then is
carried out up to the minimum level and a method where an auxiliary
coil is utilized; however, there exists no intention to limit the
present invention thereto, because the initialization method in
which the condition where B=B.sub.0, H=H.sub.0, dH/dt=H'.sub.0 can
be reproduced when therapy is resumed has the same effect.
[0088] However, the particle beam therapy system 51 according to
Embodiment 2 performs magnetic-field initialization before idle
operation; therefore, in Embodiment 2, the effect of the hysteresis
of the scanning electromagnet 3 can more sufficiently be eliminated
than in Embodiment 1.
[0089] In the case of an irradiation method in which the charged
particle beam 1 is stopped when slices are changed and the charged
particle beam 1 is continuously irradiated when irradiation is
performed within a single and the same slice, it is made possible
that a magnetic-field sensor is provided in the scanning
electromagnet 3 and through the magnetic-field sensor, the residual
magnetism can be measured before a beam is irradiated onto each
slice. By preliminarily measuring the residual magnetism, the
initialization of the scanning electromagnet 3 can be performed
based on the measured value of the residual magnetism, when the
initial step in the slice is resumed before the idle operation.
Before the idle operation is performed, the initialization of the
scanning electromagnet 3 can be performed based on the measured
value of the residual magnetism in the initial step in the slice at
which the idle operation is started. Because the initialization of
the scanning electromagnet 3 can be performed before the idle
operation is performed, operation can be implemented from the
initial step in the slice at which beam irradiation has been
interrupted or from a step that is predetermined steps prior to the
stop step. FIG. 11 represents a procedure for stopping and resuming
beam irradiation in the foregoing case.
[0090] FIG. 11 is a flowchart representing another procedure for
stopping and resuming beam irradiation in a particle beam therapy
system according to Embodiment 2. FIG. 11 differs from FIG. 10 in
that the step S11 has been replaced by the step S2 explained in
Embodiment 1. A magnetic-field sensor measures the magnetic field
of the scanning electromagnet 3 at the initial desired irradiation
position coordinates Pi in each of the slices. The irradiation
management apparatus 32 performs initialization processing for the
scanning electromagnet 3 based on the measured value of the
magnetic field at the initial desired irradiation position
coordinates Pi in the slice at which the idle operation is started.
In this method, in the case where the irradiation subject 15 is
large and hence the number of irradiation steps is large, even when
irradiation is interrupted in a latter slice, idle operation is
performed not from the initial step in actual irradiation but from
the initial step in the slice at which the irradiation has been
interrupted; therefore, the time for the idle operation can be
reduced.
[0091] In Embodiment 1, it has been explained that although in view
of the reproducibility, it is desirable to perform the idle
operation from the initial step for a given slice, a considerable
effect can still be obtained even when the idle operation is
performed from a step, empirically confirmed, that is predetermined
steps (predetermined spots) prior to the stop step. By utilizing
this method, the effect of the hysteresis of the scanning
electromagnet 3 can sufficiently be eliminated not only in the case
where initialization processing for the scanning electromagnet 3 is
performed based on the measured value of the magnetic field at the
initial desired irradiation position coordinates Pi in a given
slice, but also in the case where the initialization processing for
the scanning electromagnet 3 is performed under a predetermined
initialization condition, for example, where B=0, H=0, and dH/dt=0;
therefore, the irradiation accuracy can fall within an allowable
range.
[0092] In each of Embodiments 1 and 2, there has been explained an
irradiation method in which the charged particle beam 1 is stopped
when slices are changed, and the charged particle beam 1 is
continuously irradiated when irradiation is performed within a
single and the same slice; however, the present invention can be
applied to other irradiation methods such as the spot-scanning
method in which the charged particle beam 1 is stopped for each
irradiation spot and the raster-scanning method.
DESCRIPTION OF REFERENCE NUMERALS
[0093] 1: charged particle beam [0094] 3, 3a, 3b, 3x, 3y: scanning
electromagnet [0095] 7: position monitor [0096] 15: irradiation
subject [0097] 24: patient [0098] 32: irradiation management
apparatus [0099] 51: particle beam therapy system [0100] 54:
accelerator [0101] 78: patient sensor [0102] 84, 84a, 84b:
interlock information inputting device [0103] Ia: current
correction data [0104] Io, Ir: command current [0105] Pi: desired
irradiation position coordinates [0106] Ps: measured position
coordinates
* * * * *