U.S. patent application number 11/966383 was filed with the patent office on 2008-08-14 for apparatus for performing in vivo dosimetry.
Invention is credited to Gorgen Nilsson.
Application Number | 20080191141 11/966383 |
Document ID | / |
Family ID | 29405461 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080191141 |
Kind Code |
A1 |
Nilsson; Gorgen |
August 14, 2008 |
APPARATUS FOR PERFORMING IN VIVO DOSIMETRY
Abstract
The present invention relates to a device enabling
quantification of dose delivery in radiotherapy treatment during
patient-specific treatment of the patient utilising measurements in
predefined time-intervals with information means positioned in the
radiation beam, between the patient and the source and converting
the readings to corresponding measures in a phantom.
Inventors: |
Nilsson; Gorgen; (Storvreta,
SE) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET, SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Family ID: |
29405461 |
Appl. No.: |
11/966383 |
Filed: |
December 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10513240 |
Dec 17, 2004 |
7345274 |
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PCT/SE03/00725 |
May 6, 2003 |
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11966383 |
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60377588 |
May 6, 2002 |
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Current U.S.
Class: |
250/393 |
Current CPC
Class: |
A61N 2005/1076 20130101;
A61N 5/1042 20130101; A61N 5/1071 20130101; A61N 5/1048
20130101 |
Class at
Publication: |
250/393 |
International
Class: |
G01J 1/42 20060101
G01J001/42 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2002 |
SE |
0201371-2 |
Claims
1. An apparatus for quantifying dose delivery in radiotherapy
treatment, characterized in that it is configured for: irradiating
a phantom, obtaining fluency measurements in said phantom, and
wherein it comprises electronic circuitry configured for:
collecting information regarding the irradiation by information
means arranged between the phantom and the radiation source,
wherein said measurements are divided in time-intervals, processing
data from the measurements, and obtaining at each time-interval
information regarding the relationship between the measurements in
the phantom and the information collected by said information means
arranged between the phantom and the treatment source, which
relationship information is to be used as verification of the
treatment of a patient.
2. The apparatus in claimed in claim 1, wherein the electronic
circuitry is configured for gathering information about the
position of Multi Leaf Collimator (MLC) leafs arranged for shaping
the irradiating beam of the radiation source.
3. The apparatus as claimed in claim 2, characterized in that the
measurements in the phantom and a determination of the positions of
Multi Leaf Collimator leafs are performed simultaneously.
4. The apparatus as claimed in claim 1, characterized in that it
comprises detectors (ExtDet).
5. The apparatus as claimed in claim 4, wherein the electronic
circuitry is configured for performing measurements in the phantom
and with detectors (ExtDet) simultaneously.
6. The apparatus as claimed in any of claims 2 to 5, wherein the
electronic circuitry is configured for calculating calibration
factors from the obtained relationship information as the ratio of
the reading from information from the information means and the
measurements along the radiation ray in the phantom.
7. The apparatus as claimed in any of claims 1 to 5, characterized
in the further step of storing the data for each specific
time-interval both for measurements in the phantom and information
between the patient and the treatment source.
8. An apparatus for enabling quantification of dose delivery in
radiotherapy treatment, characterized in that it is configured for:
irradiating a phantom, obtaining measurements in said phantom
during irradiation of said phantom collecting information regarding
the irradiation by information means arranged between the phantom
and the radiation source, wherein said measurements are divided in
time-intervals, characterized in that the information means
comprises detectors (ExtDet), analysing the measurements, obtaining
at each time-interval information regarding the relationship
between the measurements in the phantom and the information
collected by said information means arranged between the phantom
and the treatment source, which relationship information is to be
used as verification of the treatment of a patient, and calculating
calibration factors from the obtained relationship information as
the ratio of the reading from information from the information
means and the measurements along the radiation ray in the phantom,
characterized in that the calibration factors are calculated
according to,
Cal.sub.n,f,seg-n,f,p,t(i),t(i+1)=S.sub.n,f,t(i),t(i+1)/(D.sub.seg-n,f,p,-
t(i),t(i+1)) where D.sub.seg-n,f,p,t(i),t(i+1) The dose in point p
in the phantom-segment defined by the DetExt detector-element, n
and the field (projection), f integrated from time t(i) until
t(i+1) S.sub.n,f,t(i),t(i+1) The signal from the ExtDet
detector-element, n, in the field, f, integrated from time t(i)
until t(i+1) Cal.sub.n,f, seg-n,f,p,t(i),t(i+1) The calibration
factor to be used with ExtDet detector-element n, in the field, f,
to convert the signal integrated from time t(i) until t(i+1) to
achieve the dose in the point p in the phantom-segment defined by
the DetExt detector-element, n and the field (projection), f
integrated from time t(i) until t(i+1).
9. The apparatus as claimed in claim 4, characterized in that it
comprises detectors (ExtDet) positioned on the surface of the
phantom.
10. The apparatus as claimed in claim 4, characterized in that it
comprises detectors (ExtDet) positioned between the radiation
source and the surface of the phantom.
11. The apparatus as claimed in claim 4, wherein the detector setup
allows for detectors (ExtDet) to be placed inside the phantom.
12. An apparatus for enabling quantification of dose delivery in
radiotherapy treatment, characterized in that it is configured to:
irradiate a phantom, obtain measurements in said phantom during
irradiation of said phantom, collect information regarding the
irradiation by information means arranged between the phantom and
the radiation source, wherein said measurements are divided in
time-intervals, characterized in that the information means
comprises the position of Multi Leaf Collimator leafs (MLC)
arranged for shaping the irradiating beam of the radiation source,
analyze the measurements, obtain information regarding the
relationship between the measurements in the phantom and the
information collected by said information means arranged between
the phantom and the treatment source at each time-interval, which
relationship information is to be used as verification of the
treatment of a patient, and calculate calibration factors from the
obtained relationship information as the ratio of the reading from
information from the information means and the measurements along
the radiation ray in the phantom, characterized in that the
calibration factors are calculated according to
Cal.sub.n,f,p,t(i),t(i+1)=F.sub.n,f,t(i),t(i+1)/(D.sub.f,p,t(i),t(i+1))
where D.sub.f,p,t(i),t(i+1) The dose in point p in the phantom at
the field (projection), f integrated from time t(i) until t(i+1)
F.sub.n,f,t(i),t(i+1) The radiation fluency in the field, f,
between the patient and the source along the ray that intersects
point p in the phantom integrated from time t(i) until t(i+1)
Cal.sub.n,f,p,t(i),t(i+1) The calibration factor describing the
relation between the fluency between the patient and the source and
the dose in the phantom.
13. The apparatus as claimed in any of claims 1 to 5 and 9 to 11,
wherein it is configured to be capable of storing in its memory a
patient specific treatment plan during irradiation of the phantom,
and verifying the accuracy of the irradiation of the phantom
comparing the measured dose in the phantom with the treatment
plan.
14. The apparatus as claimed in claim 2 or 3, wherein the
electronic circuitry is configured to, during treatment of the
patient, utilize the same positions of the MLCs as during the
irradiation of the phantom.
15. The apparatus as claimed in claim 4, wherein the electronic
circuitry is configured to, during treatment of the patient,
utilize ExtDet in the same lateral positions between the patient
and the treatment source as during the irradiation of the
phantom.
16. The apparatus as claimed in claim 15, wherein the electronic
circuitry is configured to, during treatment of patient, convert
the readings from ExtDet to dose using calculated calibration
factors for each time-interval.
17. The apparatus as claimed in claim 16, wherein the readings are
converted according to:
D.sub.seg-n,f,p,t(i),t(i+1)=S.sub.n,f,t(i),t(i+1)/Cal.sub.n,f,seg-n,f,p,t-
(i),t(i+1)
18. The apparatus as claimed in claim 12, wherein the electronic
circuitry is configured to, during treatment of the patient,
convert the information from the positions of the MLC's to dose
using said calibration factors for each time-interval.
19. The apparatus as claimed in claim 18, wherein the readings are
converted according to:
D.sub.f,p,t(i),t(i+1)=F.sub.n,f,t(i),t(i+1)/Cal.sub.n,f,p,t(i),t(i+1)
20. The apparatus as claimed in any of the claims 16 to 17, wherein
the electronic circuitry is configured to totalize the readings
from all time-intervals for each specific dose point in order to
obtain the total dose.
21. The apparatus according to claim 20, wherein the totalization
is obtained according to: D seg - n , f , p = i = 0 to T D seg - n
, f , p , t ( i ) , t ( i + 1 ) ) = i = 0 to T ( S n , f , t ( i )
, t ( i + 1 ) / Cal n , f , seg - n , f , p , t ( i ) , t ( i + 1 )
) ##EQU00003##
22. The apparatus as claimed in any of claims 18-19, wherein the
electronic circuitry is configured to totalize the readings from
all time-intervals for each specific dose point in order to obtain
the total dose, wherein the totalization is obtained according to:
D f , p = i = 0 to T D f , p , t ( i ) , t ( i + 1 ) = i = 0 to T F
n , f , t ( i ) , t ( i + 1 ) / Cal n , f , p , t ( i ) , t ( i + 1
) ##EQU00004##
23. The apparatus as claimed in claim 4, wherein it is configured
to determine the position of the ExtDet in the transversal plane
using the projection of the detectors or markers well defined to
the ExtDet utilising an image from an image device downstream the
phantom e.g. EPID or radiographic film.
24. The apparatus as claimed in any of claims 1-5, 9-11, 15-17 and
23, wherein the electronic circuitry is configured to calculate the
dose distribution using measurement of the patient anatomy and
delivered dose, using the dose distribution in a patient at one
treatment fraction or accumulated for several treatment fractions,
and to modify the subsequent treatments due to previous treatments
in order to adapt the intended dose distribution.
25. The apparatus as claimed in claim 8, wherein the electronic
circuitry is configured so that measurements in the phantom and
with detectors (ExtDet) can be performed simultaneously.
26. The apparatus as claimed in claim 12, wherein the electronic
circuitry is configured to enable measurements in the phantom and a
determination of the positions of Multi Leaf Collimator leafs to be
performed simultaneously.
Description
[0001] This application is a continuation-in-part of U.S. Ser. No.
10/513,240 filed Dec. 17, 2004, which is a national stage of PCT
application PCT/SE03/00725 filed May 6, 2003, claiming priority to
a U.S. provisional application No. 60/377,588 filed May 6, 2002,
and Swedish application number 0201371-2 filed May 6, 2002.
TECHNICAL FIELD
[0002] The present invention relates to an apparatus for
quantifying dose delivery in radiotherapy treatment intended for
use during radiotherapy treatment of a patient to verify the
accuracy of the delivered dose to the patient.
BACKGROUND OF THE INVENTION
[0003] Radiotherapy has been used to treat cancer in the human body
since early 1900. Even though radiation of cancer tumours is known
to be efficient, mortality rate for many cancers remained virtually
unchanged for a long time. The major reasons for this have been the
inability to control the primary tumour or the occurrence of
metastases. Only by improving the local control may the treatment
be more effective. In the last years Treatment Planning Systems,
TPS, in Radiation Therapy have developed extensively and is now
able to take into account the anatomy of the specific patient and
in a time efficient way plan a more optimised treatment for each
individual patient, homogenous dose to the target and minimum dose
to risk-organs.
[0004] The treatment technique to deliver this optimised treatment
is more complicated than conventional treatments because each field
must be modulated laterally in intensity and thereby compensate for
the heterogeneity and contour of the patient, the technique is
called IMRT--Intensity Modulated Radiation Therapy. The delivery
can be done using compensators, filters that reduce the intensity
to a predefined level in each part of the field due to attenuation
of the primary photon beam. However when using several fields
(4-8), each field requiring individual compensators, this technique
is time consuming and requires a lot of effort. Additionally the
attenuation of the beam also causes unwanted change of the spectral
distribution in the beam, thereby complicating the whole process.
The most common way to deliver the IMRT fields will therefore be to
use the MLC (Multi Leaf Collimator) a device that consists of thin
blocks (Leafs) that can be individually positioned to block a small
part of the field and thereby shape the beam in the lateral
direction to various irregular shapes. By moving the Leafs during
the treatment each part of the treated volume will be irradiated
during various time and thereby the intensity over the treated area
is modulated.
[0005] The new treatment technique however impose that the patient
is exactly in the position expected, something not always easy to
achieve. Additionally the requirements on accurate dose delivery
increase and thereby the requirements on quality control (QC) of
the treatment machine, the planning process and finally during the
treatment, increase. New verification and QC are to be used.
However very little has been published on measurements during
treatment, In Vivo dosimetry.
[0006] Traditional In Vivo dosimetry, measuring with a detector on
the skin of the patient to predict the dose inside the patient is
very demanding already with a fixed field (conventional therapy)
due to limitations in the TPS (Treatment Planning System) to
predict the dose distribution in the region of the patient where
externally generated secondary electrons contribute significantly
to the delivered dose e.g. build-up region (the part where the beam
enters the patient and to a depth 5-35 mm into the patient).
Thereby neither the surface or skin dose or the dose in air
up-streams the patient can be accurately predicted by the TPS in
fixed fields and the difficulty increases with a dynamically
delivered treatment. In fixed fields this is solved either by using
a special design of the detector, by general calibration or a
combination of the two. In IMRT treatments it is not that easy to
handle this either by general calibration or design due to the fact
that the varying intensity in the field is patient specific. The
traditional In Vivo dosimetry is normally not used at each fraction
and thereby the perturbation of the specially designed detectors
becomes negligible. The small margins in IMRT treatments require
extended dosimetry and quality control also at each fraction to
minimise the uncertainties and therefore the perturbation of the
detectors used in conventional therapy becomes significant.
Additionally when using IMRT, measurements must be done in many
points to verify the field's topography and the lateral position of
the detectors is very critical. To simplify the problem it has been
suggested to just measure the fluence in air. However, then the
discrepancy from the predicted values will be difficult to judge
due to lack of understandable quantification.
[0007] Alternatively to traditional in vivo dosimetry it has been
proposed to use imaging systems positioned down-streams the
patient, film or EPID (Electronic Portal Imaging Device) where the
device is calibrated to measure dose. Such a method is discussed in
"Portal dose image prediction for dosimetric treatment verification
in radiotherapy I: and algorithm for open beam", by K. I. Pasma et
al., Medical Physics 25(6), pages 830-840, 1998. A comparison can
then be done with calculated dose distribution using e.g. the TPS
(Treatment Planning System) at the position of the measuring
device. An example of this is described in "In Vivo dosimetry for
prostate cancer patients using an electronic portal imaging device;
demonstration of internal organ motion", by M. Kroonwijk et al.,
Radiotherapy and Oncology. 49(2), pages 125-132, 1998. Another
alternative is to calculate the dose distribution in the patient
from the measured dose distribution in the EPID. This is disclosed
in "Modelling the dose distribution to an EPID with collapsed cone
kernel superposition", C. Vallhagen Dahlgren et al., Workshop in
Uppsala, Mar. 13, 2001, organised by the company MDS Nordion.
[0008] The latter has the benefit of providing data that is more
easily understandable. However measurement down-streams the patient
alone will always be less accurate than combined with measurements
up-streams the patient and will thereby not distinguish if the
deviation was caused due to incorrect dose delivery by the
treatment machine or due to positioning errors or change in anatomy
of the patient (the patient might loose weight etc. from original
diagnostics). The latter is important not least in order to analyse
the root of the deviation and thereby to prevent it from occurring
in the next treatment-fraction (normally a patient receives 30
fractions before the treatment is completed).
BRIEF DESCRIPTION OF THE INVENTION
[0009] The aim of the present invention is to separate the dose
verification from the patient-positioning verification during Radio
Therapy treatment of a patient and provide a device able to perform
the dose verification. The device is configured to calibrate the
detectors to be used In Vivo (during treatment) in a time-efficient
and accurate way to achieve high quality, reliable dose
measurements during treatment.
[0010] This aim is achieved by a device having the features of
claim 1. Preferable embodiments of the invention are characterised
by the dependent claims.
[0011] According to one aspect of the invention it is characterised
by the a device able to perform irradiation of a phantom,
measurement in said phantom, measurement with detectors (ExtDet)
between the patient and the radiation source, wherein said
measurements are divided in time-intervals, and analysing the
measurements for obtaining information regarding the relationship
between the measurements in the phantom and between the patient and
the treatment source at each time-interval, which information can
be used in the treatment of the patient.
[0012] According to the invention the relationship between the
measurements may be utilised in different ways.
[0013] Because the measurements in the phantom and by the detectors
are stored in specific time-intervals a proportionality is obtained
between the measurements and a fluence reference can be defined.
This enables the calculation of calibration factors for the
detectors, which are used in the subsequent treatment of the
patient, In Vivo measurement.
[0014] The readings from such In Vivo measurements shall after
applying the calibration factors predict the dose inside a phantom
as if it was in place. The quantification of a deviation in dose
distribution can thereby be used to judge if the deviation is
acceptable or not. In most cases this verification of the dose
delivery will be sufficient, providing similar results as the
off-line verification.
[0015] The verification of the patient positioning can then be done
in a traditional way using an EPID or other methods could be used
e.g. using a diagnostic x-ray source and transmission detector in a
projection out of the treatment beam (called image guided radio
Therapy). The use of diagnostic x-ray source would have the benefit
of extensive improvement in image-contrast and thereby position
accuracy, as is well known in the art.
[0016] An alternative may be a fluence verification where a
reference value for each time-interval is obtained for the ExtDet
comparing the integrated value for all time intervals with an
integrated measurement in the phantom. A combination with back
projection from the EPID-images or as an input to the treatment
planning system could give quantitative dose data in the
patient.
[0017] After verifying major deviations in dose delivery and/or
patient positioning a second step can be to combine the two and
thereby predict the dose distribution in the patient for more
precise checks of dose to the tumour, risk-organs etc. This data
from one fraction or accumulated for several fractions can be used
to modify the treatment plan for the remaining treatment fractions
and thereby compensate for the earlier deviations. Such an adaptive
treatment technology can be updated after each fraction if
required.
[0018] Another alternative to measure the fluence with the detector
up-streams the patient, ExtDet, is to calculate the fluence using
any information of the MLC positions as input and then calibrate
that fluence using the described method, eg. calibrate the fluence
for each time interval to dose measured in the phantom during the
pre treatment verification. Such a determination of the dose in the
phantom will be limited in accuracy and verification compared to
the use of an ExtDet but still very useful because it enables
quantification of deviations during treatment as dose in the
phantom as if it was in place.
[0019] Radio Therapy is developing towards improved tumor control
with reduced side effects. The era after IMRT may comprise IMAT
(Intensity Modulated ARC Therapy--rotation therapy), VMAT
(Volumetric Modulated Arc Therapy; an extension of IMAT including
dose rate modulation), Gating (irradiation during a limited part of
and synchronized with the respiratory cycle), 4DRT (tumor tracking,
reduced margin where beam follows the target motion) and
TomoTherapy (helical therapy). The new treatment techniques are a
challenge to dosimetry and QA during treatment and prior to
treatment. A measurement system will consequently need to measure
dose distribution with time resolution intervals as described above
both to gain accuracy and to make it possible to divide the
treatment into sub-treatments and thereby make the analysis of
discrepancies possible.
[0020] A measurement system where the doses measured at short time
intervals are combined with, and tagged to, information on external
machine parameters and on-line patient anatomy localization will
make it possible to verify the new treatment modalities. External
machine parameters include: beam pulse synchronisation; beam
shaping e.g. MLC leaf positioning; beam direction in relation to
patient; and fluency shaping devices e.g. MLC etc. Patient anatomy
localizers are devices that directly or indirectly detect the
actual position of the target e.g. X-ray systems; localizers for
implants etc.
[0021] These and other aspects of, and advantages with, the present
invention will become apparent from the following detailed
description and from the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In the following detailed description, reference will be
made to the accompanying drawings, of which
[0023] FIG. 1a schematically shows a treatment machine to which a
phantom is arranged, which in turn is provided with detectors,
[0024] FIG. 1b schematically shows the arrangement of FIG. 1a but
with a human body instead of the phantom,
[0025] FIG. 2a schematically shows the machine of FIG. 1a but with
a 2D detector device arranged between the machine and the
phantom,
[0026] FIG. 2b schematically shows the arrangement of FIG. 2a but
with a human body instead of the phantom,
[0027] FIG. 3 is a schematic view of a radiation beam, and
[0028] FIG. 4 shows off-line verification of a treatment plan.
DETAILED DESCRIPTION OF THE INVENTION
[0029] A radiotherapy device utilised for treating tumours with
radiation is shown schematically in FIGS. 1-2 and is generally
denoted with reference numeral 10. The device comprises a
radiotherapy system capable of emitting a beam 12 of electrons or
photons from a treatment head. The radiotherapy system is provided
with conventional field-shaping device (not shown), for example an
MLC, for allowing the lateral shape of the beam to be altered so as
to shield off non-affected areas of the body and concentrate the
beam to the tumour. Control means (not shown) are provided for the
radiotherapy system.
[0030] A table 22 is arranged for a patient 20 to lie on. The table
is rotatable around a vertical axis, and movable horizontally and
vertically in order to place the area to be treated of the patient
in the area of the beam. Further, the apparatus according to the
invention utilises different detectors for measuring the radiation
emitted from the radiotherapy device. They may for example comprise
real-time detectors for measurement on surface/skin 14, such as
semiconductor detector, gas detector, scintillator detector etc.
The detector device might be thin or including a build-up to reduce
the dependency on scatter radiation. It might also be designed in a
way that it is evenly thick measured in g/cm2 over its entire area
thereby taking into account the various density in encapsulation
and the detector itself at a typical beam modality.
[0031] The detectors may also be detectors for measurement
in-between radiation source and phantom/patient like for example
imaging systems such as film or EPID. The detectors are connected
to suitable signal processing means (not shown). The above
mentioned details are well known to the man skilled in the art and
will not be described in detail. The apparatus according to the
present invention is adapted to utilise the above-mentioned
equipment in order to enable quantification of dose delivery in
radiotherapy treatment, in particular during patient-specific
treatment of the patient (from now on called In Vivo) utilising
measurements in predefined time-interval with detectors (from now
on called ExtDet) positioned in the radiation beam, between the
patient and the source and converting the readings to corresponding
measures in a phantom using the proportionality between the
measurements of the detectors and the measures in the phantom.
[0032] An apparatus according to the present invention is further
aimed at preferably obtaining calibration factors for the ExtDet.
The said calibration factors are obtained for each ExtDet per point
in the defined segment in the phantom 36, FIG. 3, and said
definable time-interval for each field simultaneously irradiating
the ExtDet and said phantom including detectors to measure the
absorbed dose using the said patient-specific treatment without
patient (from now on called off-line).
[0033] An example of a method for utilising an apparatus according
to the invention may be described with the following steps: [0034]
An individual treatment plan for the patient is made using a
Treatment Planning System (TPS). The anatomy of the patient is then
defined using diagnostic equipment e.g. CT, Computerised Tomography
and the radiation characteristics of the treatment device is
defined generally by measurements both imported in the TPS. The
target-volume and risk-organs are defined and then the optimum plan
for the treatment is made where criteria as maximum dose to the
risk-organs and the minimum dose to the target etc. is used. The
outcome of the plan is information that will be used by the
treatment machine to define projections, beam modality, field
shapes and movement of the MLC-leaves etc. [0035] The patient
specific treatment plan, in the TPS, is applied on a phantom,
suitable for dose measurements, and the dose distribution inside
the phantom is calculated. [0036] Prior to treatment, off-line, a
physical phantom, identical to the one used in the calculation, is
irradiated using the patient specific treatment. The dose
distribution inside the phantom is measured to verify the
integrated dose comparing the measurement and the plan for a
complete field, sub-field or fraction (off-line quality control or
pre treatment verification). Additionally the dose distribution is
measured for each field, in all measurement points in the phantom
for each time-interval, defined by appropriate time or
synchronisation to the treatment machine of the Intensity Modulated
field, and stored. The above procedure is shown in FIG. 4. [0037]
Simultaneously as measuring inside the phantom, off-line, the dose
is also measured using external detectors, ExtDet, on the phantom
surface or in any position in the beam between the phantom and the
treatment source using the same time-interval as in the phantom
measurements or synchronized to it. This step may also be done by
first placing detectors inside the phantom and measure the
irradiation for each time interval and then to place the detectors
upstream the phantom, reproduce the previous irradiation conditions
and measure it for each time interval. With this solution the same
detectors may be used for both measurements. The obtained reading
for each ExtDet, for each field and time-interval and interval will
then be used to calculate the calibration factors together with the
dose values in the phantom. Either the obtained readings are
firstly stored and subsequently the calibration factors are
calculated, or they are calculated immediately. The calibration
factors are preferably calculated according to
[0037]
Cal.sub.n,f,seg-n,f,p,t(i),t(i+1)=S.sub.n,f,t(i),t(i+1)/(D.sub.se-
g-n,f,p,t(i),t(i+1)), where
[0038] D: Absorbed dose measured in the phantom with know shape,
positioning and orientation during a certain time interval
[0039] S: The integrated signal from the ExtDet
[0040] n: Detector-element in ExtDet, 32 in FIG. 3
[0041] f: The specific field (one projection of the beam defined by
a field-identity)
[0042] seg: A segment in the phantom described as the shadowed
volume of one specific detector-element in the ExtDet, n and in one
specific projection defined by the field, f, 36 in FIG. 3
[0043] p: Well defined point in the segment
[0044] Cal: The calibration factor
[0045] t(i): Time at start of interval i, t(0) is the start time
for the sequence.
[0046] t(i+1): Time at start of interval i+1, t(T) is the end of
the sequence.
[0047] D.sub.seg-n,f,p,t(i),t(i+1) The dose in point p in the
phantom-segment defined by the DetExt detector-element, n and the
field (projection), f integrated from time t(i) until t(i+1)
[0048] S.sub.n,f,t(i),t(i+1) The signal from the ExtDet
detector-element, n, in the field, f, integrated from time t(i)
until t(i+1)
[0049] Cal.sub.n,f,seg-n,f,p,t(i),t(i+1) The calibration factor to
be used with ExtDet detector-element n, in the field, f. To convert
the signal integrated from time t(i) until t(i+1) to achieve the
dose in the point p in the phantom-segment defined by the DetExt
detector-element, n and the field (projection), f integrated from
time t(i) until t(i+1) [0050] During treatment of the patient the
reading by each of the ExtDet can now be converted to dose in the
points in respectively segment in the phantom, as if it was in
place, using the said calibration factors for each time-interval
according to
[0050]
D.sub.seg-n,f,p,t(i),t(i+1)=S.sub.n,f,t(i),t(i+1)/Cal.sub.n,f,seg-
-n,f,p,t(i),t(i+1)
[0051] The readings from all time-intervals for each specific dose
point in the phantom can be totalised to present the total dose in
that point for each respectively field according to
D seg - n , f , p = i = 0 to T D seg - n , f , p , t ( i ) , t ( i
+ 1 ) ) = i = 0 to T ( S n , f , t ( i ) , t ( i + 1 ) / Cal n , f
, seg - n , f , p , t ( i ) , t ( i + 1 ) ) ##EQU00001##
[0052] The dose from all fields to each specific point can then be
totalised to present the total dose in all points for the complete
treatment fraction (a complete treatment consists of several
fractions given over several days or weeks). The total dose in each
point can directly be compared with the result from the treatment
planning system when applied on the phantom similar to the off-line
verification (pre treatment verification).
[0053] Deviations between the measured and calculated dose values
can be analysed by using the data for each time-interval and
thereby simplifying the analysing phase.
[0054] If the deviation is caused by incorrect motion of the leaves
the calculated dose value in the phantom might be slightly
incorrect and in such a case the exact value can be verified using
a phantom measurement simulating the motion during the
miss-delivered treatment.
[0055] The position of the ExtDet can be determined in the
transversal plane on the phantom and in particular on the patient
using the projection of the detectors or markers well defined to
the ExtDet utilising the image from an image device down streams
the phantom e.g. EPID or radiographic film.
[0056] Incorrect positioning of the patient in the field compared
to the detector can be visualised using markers on the detector
device that light-up on the EPID image e.g. lead-seeds. Using
several projections the positioning of the patient can be
defined.
[0057] The alternative of a fluence verification of the integrated
dose in the phantom with the treatment plan and simultaneously
measured reference signals with ExtDet in each time-interval where
the (S.sub.n,f,t(i),t(i+1) is proportional to the
(D.sub.seg-n,f,p,t(i),t(i+1) makes it possible to estimate the
deviation in fluence for each time-interval during treatment
although it is not directly convertible into dose in the
phantom.
[0058] An alternative to measure the fluence with the detector
up-streams the patient, ExtDet, is to calculate the fluence using
any information of the MLC positions as input and then calibrate
that fluence using the described method, eg. calibrate the fluence
for each time interval to dose measured in the phantom during the
pre treatment verification. Such a determination of the dose in the
phantom will be limited in accuracy and verification compared to
the use of an ExtDet but still very useful because it enables
quantification of deviations during treatment as dose in the
phantom as if it was in place. The information regarding the MLC
positions is easily obtainable since there is already provided
means in the radio therapy device for controlling the position of
the MLC leaves. This information can then be used in the comparison
with the measurements inside the phantom.
[0059] When using the information of the MLC positions, the
calibration factors may be calculated according to
Cal.sub.n,f,p,t(i),t(i+1)=F.sub.n,f,t(i),t(i+1)/(D.sub.f,p,t(i),t(i+1))
where [0060] D.sub.f,p,t(i),t(i+1) The dose in point p in the
phantom at the field (projection), f integrated from time t(i)
until t(i+1) [0061] F.sub.n,f,t(i),t(i+1) The radiation fluency in
the field, f, between the patient and the source along the ray that
intersects point p in the phantom integrated from time t(i) until
t(i+1) [0062] Cal.sub.n,f,p,t(i),t(i+1) The calibration factor
describing the relation between the fluency between the patient and
the source and the dose in the phantom.
[0063] The readings from all time-intervals for each specific dose
point in the phantom can be totalised to present the total dose in
that point for each respectively field according to
D f , p = i = 0 to T D f , p , t ( i ) , t ( i + 1 ) = i = 0 to T F
n , f , t ( i ) , t ( i + 1 ) / Cal n , f , p , t ( i ) , t ( i + 1
) ##EQU00002##
[0064] The method for utilising an apparatus according to the
invention may be implemented in the control and measurement system
of the radiotherapy device, and thereby using the processor and
storage means available there. It may of course be implemented in a
stand-alone unit comprising the necessary equipment such as a
central processing unit CPU performing the steps of the method.
This is performed with the aid of a dedicated computer program,
which is stored in the program memory. It is to be understood that
the computer program may also be run on a general purpose
industrial computer instead of a specially adapted computer.
[0065] The software includes computer program code elements or
software code portions that make the computer perform the method
using equations, algorithms, data and calculations previously
described. A part of the program may be stored in a processor as
above, but also in a ROM, RAM, PROM or EPROM chip or similar. The
program in part or in whole may also be stored on, or in, other
suitable computer readable medium such as a magnetic disk, CD-ROM
or DVD disk, hard disk, magneto-optical memory storage means, in
volatile memory, in flash memory, as firmware, or stored on a data
server.
[0066] It is to be understood that the above description of the
invention and the accompanying drawings is to be regarded as a
non-limiting example thereof and that the scope of protection is
defined by the appended patent claims.
* * * * *