U.S. patent application number 17/237436 was filed with the patent office on 2021-12-23 for charged particle irradiation apparatus.
This patent application is currently assigned to B dot Medical Inc.. The applicant listed for this patent is B dot Medical Inc.. Invention is credited to Takuji FURUKAWA, Yousuke HARA, Yoshiaki TAKI, Ryohei TANSHO.
Application Number | 20210393984 17/237436 |
Document ID | / |
Family ID | 1000006010518 |
Filed Date | 2021-12-23 |
United States Patent
Application |
20210393984 |
Kind Code |
A1 |
TANSHO; Ryohei ; et
al. |
December 23, 2021 |
CHARGED PARTICLE IRRADIATION APPARATUS
Abstract
Provided is a charged particle irradiation apparatus that
performs scanning with a charged particle beam and irradiates an
irradiation target spot by spot. An embodiment of the present
invention provides a charged particle irradiation apparatus (10)
including: a first dose monitor (54) mounted in an irradiation
nozzle (50); an irradiation pattern converting device (70) that
generates irradiation control data used for controlling the charged
particle irradiation apparatus (10) from treatment plan data
including information on a dose rate and a dose of a charged
particle beam for each spot; and a dose correction factor storage
unit (72) that stores data of a dose correction factor with respect
to a dose rate of a charged particle beam. The irradiation pattern
converting device (70) is configured to select one spot in the
treatment plan data, for instance.
Inventors: |
TANSHO; Ryohei; (Tokyo,
JP) ; TAKI; Yoshiaki; (Tokyo, JP) ; FURUKAWA;
Takuji; (Tokyo, JP) ; HARA; Yousuke; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
B dot Medical Inc. |
Tokyo |
|
JP |
|
|
Assignee: |
B dot Medical Inc.
Tokyo
JP
|
Family ID: |
1000006010518 |
Appl. No.: |
17/237436 |
Filed: |
April 22, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 5/1077 20130101;
A61N 5/1071 20130101; A61N 2005/1087 20130101; A61N 5/103 20130101;
A61N 5/1067 20130101 |
International
Class: |
A61N 5/10 20060101
A61N005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2020 |
JP |
2020-104390 |
Claims
1. A charged particle irradiation apparatus that performs scanning
with a charged particle beam and irradiates an irradiation target
spot by spot, the charged particle irradiation apparatus
comprising: a first dose monitor mounted in an irradiation nozzle;
an irradiation pattern converting device that generates irradiation
control data used for controlling the charged particle irradiation
apparatus from input of treatment plan data including information
on a dose rate and a dose of a charged particle beam for each spot,
wherein the treatment plan data includes information on energy, a
dose rate, and a beam size of a charged particle beam for each spot
and a spot position; and a dose correction factor storage unit that
stores data of a dose correction factor R1 with respect to a
combination of energy, a dose rate, and a beam size of a charged
particle beam and data of a dose correction factor R2 with respect
to a spot position, wherein the irradiation pattern converting
device is configured to (i) select one spot in the treatment plan
data, (ii) acquire a corresponding dose correction factor R1 from
the dose correction factor storage unit by using energy, a dose
rate, and a beam size of a charged particle beam, which correspond
to the selected spot and are included in the treatment plan data,
as a key, (iii) acquire a corresponding dose correction factor R2
from the dose correction factor storage unit by using a spot
position, which corresponds to the selected spot and is included in
the treatment plan data, as a key, (iv) correct a dose value
corresponding to the selected spot by multiplying a dose value,
which corresponds to the selected spot and is included in the
treatment plan data, by the dose correction factors R1 and R2
acquired in processes of the (ii) and (iii), respectively, and (v)
perform processes of the (i) to (iv) on all of spots in the
treatment plan data, and (vi) generate irradiation control data for
a dose by using corrected dose data for all of spots in the
treatment plan data, and wherein the charged particle irradiation
apparatus corrects a difference between an actual dose delivered in
an irradiation target and a dose measured by the first dose
monitor, wherein the difference is caused by influence of ion
recombination in the first dose monitor.
2. (canceled)
3. The charged particle irradiation apparatus according to claim 1
further comprising: a second dose monitor inside the irradiation
nozzle; and a dose monitor output correction factor storage unit
that stores data of an output correction factor used for correcting
output of the second dose monitor with respect to energy of a
charged particle beam, wherein the second dose monitor is arranged
in downstream of the first dose monitor, and wherein a monitor unit
measured by the second dose monitor is corrected spot by spot by
being multiplied by an output correction factor corresponding to
energy of a charged particle beam stored in the dose monitor
output-correction factor storage unit.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a charged particle
irradiation apparatus that performs scanning with a charged
particle beam and irradiates an irradiation target spot by spot
(also referred to as "scanning irradiation").
Description of the Related Art
[0002] Conventionally, particle therapy treatment to irradiate a
malignant tumor such as a cancer with a charged particle beam (also
referred to as "particle ray") accelerated by high energy and treat
the malignant tumor has been employed. In recent years, in particle
therapy treatment using a charged particle beam such as a proton or
a carbon, a new irradiation method called scanning irradiation has
been paid attention, and the number of facilities that implement
the scanning irradiation has increased. In the conventional
particle therapy treatment, a broad beam irradiation method that
statically expands a charged particle beam that is thin in the
lateral direction (irradiation slice plane direction) and the
traveling direction (depth (thickness) direction) by using various
irradiation field forming devices (for example, a scatterer, a
ridge filter, a collimator, or a patient bolus) is the mainstream.
In the scanning irradiation method, however, a charged particle
beam is three-dimensionally, dynamically controlled to form an
irradiation field without using such an irradiation field forming
device, and therefore improvement of a dose distribution to an
irradiation target is expected.
[0003] Japanese Patent Application Laid-Open No. 2002-228755
discloses a technology in which a relationship between the
absorption dose calculated from a measurement of an ionization
chamber measured in advance and collection efficiency of the
ionization chamber is recorded and, based on this recorded
relationship, the absorption dose calculated from the ionization
chamber is corrected by the collection efficiency.
[0004] International Publication No. 2012/120677 discloses a
technology that finds a correction factor for a dose measured by a
dose monitor corresponding to the irradiation position of an
irradiation object to compensate deterioration of dose measurement
accuracy due to deflection of an electrode of the dose monitor,
corrects the sensitivity of the dose monitor, and thereby enables
accurate dose measurement.
[0005] In the particle therapy treatment, it is important to
irradiate a patient with a (planned) dose set by a medical doctor
and the like, and it is therefore required to accurately measure
the irradiated dose. In general, a dose is measured by using a dose
monitor also called an ionization chamber provided to an
irradiation nozzle near an irradiation target (affected part). In
measurement of a dose of a charged particle beam performed by a
dose monitor, however, the measurement accuracy may be deteriorated
because of influence of ion recombination and the like. Thus, there
may be a difference between a dose actually irradiated to an
irradiation target and a dose measured by a dose monitor.
SUMMARY OF THE INVENTION
[0006] In view of the above, the present invention intends to
provide a charged particle irradiation apparatus that performs
scanning with a charged particle beam and irradiates an irradiation
target spot by spot.
[0007] The present invention includes the following aspects [1] to
[3]:
[0008] [Aspect 1] A charged particle irradiation apparatus (10)
that performs scanning with a charged particle beam and irradiates
an irradiation target spot by spot, the charged particle
irradiation apparatus (10) including:
[0009] a first dose monitor (54) mounted in an irradiation nozzle
(50);
[0010] an irradiation pattern converting device (70) that generates
irradiation control data used for controlling the charged particle
irradiation apparatus (10) from input of treatment plan data
including information on a dose rate and a dose of a charged
particle beam for each spot; and
[0011] a dose correction factor storage unit (72) that stores data
of a dose correction factor R with respect to a dose rate of a
charged particle beam,
[0012] wherein the irradiation pattern converting device (70) is
configured to [0013] (i) select one spot in the treatment plan
data, [0014] (ii) correct a dose value corresponding to the
selected spot by using a dose rate, which corresponds to the
selected spot and is included in the treatment plan data, as a key
to acquire a dose correction factor R corresponding to the dose
rate from the dose correction factor storage unit (72) and
multiplying a dose value corresponding to the selected spot and
included in the treatment plan data by the dose correction factor
R, [0015] (iii) perform processes of the (i) and (ii) on all of
spots in the treatment plan data, and [0016] (iv) generate
irradiation control data for a dose by using corrected dose data
for all of spots in the treatment plan data, and
[0017] wherein the charged particle irradiation apparatus corrects
a difference between an actual dose delivered in an irradiation
target and a dose measured by the first dose monitor, wherein the
difference is caused by influence of ion recombination in the first
dose monitor.
[0018] [Aspect 2] The charged particle irradiation apparatus
according to Aspect 1,
[0019] wherein the treatment plan data includes information on
energy, a dose rate, and a beam size of a charged particle beam for
each spot and a spot position,
[0020] wherein the dose correction factor storage unit (72) stores
data of a dose correction factor R1 with respect to a combination
of energy, a dose rate, and a beam size of a charged particle beam
and data of a dose correction factor R2 with respect to a spot
position, and
[0021] wherein the irradiation pattern converting device (70)
[0022] (i) selects one spot in the treatment plan data, [0023] (ii)
acquires a corresponding dose correction factor R1 from the dose
correction factor storage unit (72) by using energy, a dose rate,
and a beam size of a charged particle beam, which correspond to the
selected spot and are included in the treatment plan data, as a
key, [0024] (iii) acquires a corresponding dose correction factor
R2 from the dose correction factor storage unit (72) by using a
spot position, which corresponds to the selected spot and is
included in the treatment plan data, as a key, [0025] (iv) corrects
a dose value corresponding to the selected spot by multiplying a
dose value, which corresponds to the selected spot and is included
in the treatment plan data, by the dose correction factors R1 and
R2 acquired in processes of the (ii) and (iii), respectively, and
[0026] (v) performs processes of the (i) to (iv) on all of spots in
the treatment plan data, and [0027] (vi) generates irradiation
control data for a dose by using corrected dose data for all of
spots in the treatment plan data.
[0028] [Aspect 3] The charged particle irradiation apparatus
according to Aspect 1 or 2 further including:
[0029] a second dose monitor (55) inside the irradiation nozzle
(50); and
[0030] a dose monitor output correction factor storage unit (74)
that stores data of an output correction factor used for correcting
output of the second dose monitor (55) with respect to energy of a
charged particle beam,
[0031] wherein the second dose monitor (55) is arranged in
downstream of the first dose monitor (54), and
[0032] wherein a monitor unit measured by the second dose monitor
(55) is corrected spot by spot by being multiplied by an output
correction factor corresponding to energy of a charged particle
beam stored in the dose monitor output-correction factor storage
unit (74).
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a schematic diagram of a configuration of a
charged particle irradiation apparatus of a first embodiment.
[0034] FIG. 2A and FIG. 2B are schematic diagrams of an irradiation
nozzle and a scanning irradiation.
[0035] FIG. 3A and FIG. 3B are graphs illustrating relationships of
the dose of a dose monitor and the actual dose with respect to the
dose rate.
[0036] FIG. 4 is a flowchart of particle therapy treatment of the
first embodiment.
[0037] FIG. 5A and FIG. 5B are graphs illustrating relationships of
the energy and the beam size with respect to a charge density.
[0038] FIG. 6A is a schematic sectional view of an ionization
chamber, and FIG. 6B is a graph illustrating a relationship between
the dose monitor output and the inter-electrode distance d.
[0039] FIG. 7A and FIG. 7B illustrate examples of energy, dose
rates, and beam size dose correction factors of a charged particle
beam and spot position dose correction factors.
[0040] FIG. 8 is a flowchart of particle therapy treatment of a
second embodiment.
[0041] FIG. 9A and FIG. 9B are schematic diagrams of an irradiation
nozzle and an irradiation pattern converting device of the second
embodiment.
[0042] FIG. 10 is a graph illustrating a relationship between
output ratios of first and second dose monitors and the energy.
[0043] FIG. 11 is a diagram illustrating calculation of a dose
correction factor.
DESCRIPTION OF THE EMBODIMENTS
First Embodiment
[0044] The first embodiment of the present invention relates to a
charged particle irradiation apparatus that performs scanning with
a charged particle beam and irradiates an irradiation target spot
by spot. In particular, the charged particle irradiation apparatus
of the present embodiment mainly corrects a difference between an
actual dose delivered in an irradiation target and a dose measured
by a dose monitor, and the difference is caused by influence of ion
recombination in the dose monitor provided to an irradiation
nozzle.
[0045] Charged Particle Irradiation Apparatus 10
[0046] FIG. 1 is a schematic diagram of a configuration of a
charged particle irradiation apparatus 10, and FIG. 2A and FIG. 2B
are schematic diagrams of an irradiation nozzle 50 and scanning
irradiation.
[0047] The charged particle irradiation apparatus 10 has an
accelerator 20, a charged particle beam transport system 30, a
focusing magnet 40, and an irradiation nozzle 50. Further, the
charged particle irradiation apparatus 10 has a treatment planning
system 60, an irradiation pattern converting device 70, and an
irradiation control device 80.
[0048] The accelerator 20 is a device that generates a charged
particle beam, which is a synchrotron, a cyclotron, or a linear
accelerator, for example. The charged particle beam generated by
the accelerator 20 is guided to the focusing magnet 40 through the
charged particle beam transport system 30.
[0049] The charged particle beam transport system 30 includes one
or multiple charged particle beam adjustment units 31, a vacuum
chamber 32, a bending magnet 33, a sector-shaped vacuum chamber 34,
and the like. The accelerator 20, the charged particle beam
adjustment units 31, and the bending magnet 33 are connected via
the vacuum chambers 32, and the bending magnet 33 and the focusing
magnet 40 are connected via the sector-shaped vacuum chamber 34.
The charged particle beam adjustment units 31 includes a beam slit
used for adjusting the beam shape and/or the dose of a charged
particle beam, an electromagnet used for adjusting the traveling
direction of a charged particle beam, a quadrupole magnet used for
adjusting the beam shape of a charged particle beam, a steering
magnet used for fine-tuning the beam position of a charged particle
beam, and the like as appropriate in accordance with the
specification.
[0050] The bending magnet 33 continuously deflects a charged
particle beam at the deflection angle (.PHI.) and launches the
charged particle beam to the focusing magnet 40. When the traveling
direction of a charged particle beam is defined as an X-axis, the
direction of a magnetic field generated by the focusing magnet 40
is defined as a Z-axis, and the direction orthogonal to the X-axis
and the Z-axis is defined as a Y-axis, the focusing magnet 40
converges a charged particle beam, which is incident from a wide
range of a deflection angle (.PHI.) relative to the X-axis, into
the isocenter (O) at an irradiation angle (.theta.) on the XY plane
through the irradiation nozzle 50. The bending magnet 33 and the
focusing magnet 40 are those described in prior patent documents
(Japanese Patent No. 6364141, Japanese Patent No. 6387476, Japanese
Patent Application No. 2020-63275) filed by the present applicant,
which are incorporated herein by reference, and detailed
description thereof is omitted.
[0051] The irradiation nozzle 50 is located inside a treatment room
in which treatment using a charged particle beam and the like are
performed and continuously moves along the shape on the exit side
of an effective magnetic field region generated by the focusing
magnet 40 on the XY plane. The charged particle beam traveling from
the exit side of the effective magnetic field region to the
isocenter passes inside the irradiation nozzle 50, and a scan with
the charged particle beam is performed by the irradiation nozzle
50.
[0052] With respect to a difference between adjustment of the
irradiation position using a change of the irradiation angle
(.theta.) and adjustment of the irradiation position using a scan
with a charged particle beam performed by a scanning magnet 52
inside the irradiation nozzle 50, it can be understood that
relatively coarse adjustment of the irradiation position of a
charged particle beam is performed with a change of the irradiation
angle .theta., and relatively fine adjustment (fine tune) of the
irradiation position of a charged particle beam is performed with a
scan with a charged particle beam by a scanning magnet 52, although
not limited thereto. In both the cases, adjustment of the
irradiation position in the depth (thickness) direction of an
irradiation target can be performed by changing the energy of the
charged particle beam.
[0053] The irradiation nozzle 50 has the scanning magnet 52, a dose
monitor 54, and a position monitor 56. The energy of a charged
particle beam may be adjusted by providing an energy adjustment
unit such as a range shifter to the irradiation nozzle 50, may be
adjusted on the accelerator 20 side, or may be adjusted by both of
the above.
[0054] By adjusting the amount of flowing current or the direction
of the current of the scanning magnet 52, it is possible to
fine-tune the traveling direction of a charged particle beam
launched from the irradiation nozzle 50, change the irradiation
position of the charged particle beam, and perform a scan
(scanning) of the charged particle beam.
[0055] The dose monitor 54 is an ionization chamber that monitors a
charged particle beam and measures the dose of the charged particle
beam. The ionization chamber is a radiation detector in which
two-polarity electrodes are installed inside a container filled
with a gas. When an ionized radiation such as charged particles
enters the ionization chamber, the internal gas is ionized into
electrons and positive ions. A voltage is applied between
electrodes inside the ionization chamber, the ionized electrons and
positive ions move to the positive electrode and the negative
electrode, respectively, and current occurs. This current is
measured, and thereby the dose of a charged particle beam is
measured.
[0056] The position monitor 56 measures the position of a passing
charged particle beam and measures the position of a charged
particle beam at an irradiation target.
[0057] In the scanning irradiation, an irradiation target is
divided into multiple slice layers (also referred to as irradiation
slice planes), and each slice layer is divided into multiple spots.
In general, the number of spots may be up to several ten thousands
even for a typical irradiation target size (several hundreds
cm.sup.3). The position of a charged particle beam is adjusted by
the scanning magnet 52, and irradiation is performed as if spots
are filled one by one (FIG. 2B). The position of the charged
particle beam is measured by the position monitor 56, and the dose
to each spot is measured by the dose monitor 54. When the dose
value measured by the dose monitor 54 reaches a preset value
(targeted dose) set in advance by a medical worker such as a
medical doctor for each spot (irradiation completion), the charged
particle beam is moved to the next spot position. When irradiation
to all the spots on one slice plane ends, the irradiation of the
charged particle beam is temporarily stopped, and irradiation of
the next slice plane (in the depth direction) is then prepared.
With repetition of this flow, the entire irradiation target is
irradiated with the charged particle beam, and when all the spots
of the irradiation target are finally irradiated with a targeted
dose, the beam irradiation is completely stopped, and the treatment
ends.
[0058] When a different slice plane is irradiated, the energy of a
charged particle beam is changed. The change of energy can be
performed by changing the output of the accelerator 20 to change
the energy of a charged particle beam or using an energy adjustment
unit such as a range shifter for the irradiation nozzle 50. In
response to completion of setting for energy change, spot
irradiation in the next slice is started. The entire irradiation
target is irradiated by repetition of the above flow, and when
irradiation of the targeted doses set for all the spots of the
irradiation target is completed, the irradiation of the charged
particle beam is stopped.
[0059] The treatment planning system 60 generates treatment plan
data based on input from a medical worker and transmits the
generated treatment plan data to the irradiation pattern converting
device 70. The treatment plan data is generated by a medical worker
specifying the range of a tumor (irradiation target) based on a CT
image and/or an MRI image of a patient secured on a treatment stage
of a treatment room to specify the tumor shape, specifying an
irradiating dose, a dose rate, and the like in the treatment
planning system 60.
[0060] The treatment plan data includes information on a dose rate
and a dose of a charged particle beam for each spot and spot
positions (coordinates). The treatment plan data may further
include information on energy and a beam size of a charged particle
beam for each spot, a position and a size of a tumor (irradiation
target), an irradiation range (an irradiation direction and the
like) of a charged particle beam to a tumor, and the like.
[0061] Herein, information handled in the treatment plan data is
based on patient CT information and the like and thus is unable to
be used directly for irradiation by the charged particle
irradiation apparatus 10 and the like, for example. Therefore,
conversion from treatment plan data into irradiation control data
is required. For example, in the treatment plan data, values of a
dose, a dose rate, energy, and the like for each spot are
determined so as to provide a planned dose to an irradiation
target. In the actual irradiation, since a dose inside an
irradiation target, that is, inside a patient body is unable to be
measured, the dose monitor 54 using an ionization chamber serves
such a function. The dose monitor 54 is formed of an ionization
chamber and a circuit such as an electrometer. Current ionized by a
charged particle beam that has passed through the ionization
chamber is converted into a corresponding frequency by the circuit
and output as a pulse signal, and the dose monitor 54 counts the
pulse signal. Therefore, the dose for each spot in the treatment
plan data is handled in a unit specific to radiation therapy that
is called a monitor unit (MU) in irradiation control data and
associates a count value of pulse signals with a dose.
[0062] The irradiation pattern converting device 70 generates
irradiation control data based on treatment plan data received from
the treatment planning system 60 and transmits the generated
irradiation control data to the irradiation control device 80. In
the scanning irradiation method, various parameters such as a dose
rate, a dose, energy, and the like of a charged particle beam in
the irradiation control data are set spot by spot. Thus, correction
to measurement values from the dose monitor 54 is required to be
performed spot by spot.
[0063] That is, in response to receiving treatment plan data from
the treatment planning system 60, the irradiation pattern
converting device 70 accesses a dose correction factor storage unit
72 and acquires a dose correction factor related to an associated
dose rate by using a dose rate for each spot specified in the
treatment plan data as a key. The dose correction factor storage
unit 72 may be provided in the irradiation pattern converting
device 70 or may be configured as a device separated from the
irradiation pattern converting device 70.
[0064] Then, after correcting the dose for each spot specified by
the treatment plan data by using the dose correction factor, the
irradiation pattern converting device 70 generates irradiation
control data and transmits the generated irradiation control data
to the irradiation control device 80. The irradiation control data
includes control information on the accelerator 20, the charged
particle beam transport system 30, the focusing magnet 40, and the
irradiation nozzle 50 (for example, a power supply current value of
the accelerator 20, current control of the charged particle beam
transport system 30 and the focusing magnet 40, drive control of
the irradiation nozzle 50, and the like) and the like.
[0065] The irradiation control device 80 controls the accelerator
20, the charged particle beam transport system 30, the focusing
magnet 40, and the irradiation nozzle 50 to control irradiation of
a charged particle beam to an irradiation target in accordance with
scanning irradiation based on irradiation control data received
from the irradiation pattern converting device 70 and performs
treatment by using a charged particle beam in accordance with the
scanning irradiation method.
[0066] Dose Correction
[0067] In measurement using the dose monitor 54 (ionization
chamber), a primary factor of deterioration in the accuracy of dose
measurement is influence caused by ion recombination in the
ionization chamber. Ion recombination is a phenomenon that
electrons and positive ions ionized by a radioactive ray recombine
before reaching electrodes. Since occurrence of ion recombination
reduces the generated current amount, the measurement value of the
dose monitor 54 will indicate a value that is lower than a dose of
the actually irradiated charged particle beam. Ion recombination
includes initial ion recombination and general ion recombination,
and it is known that, while the initial ion recombination does not
depend on the dose rate of a radiation (a dose per unit time), the
occurrence rate of the general ion recombination increases as the
dose rate increases. Thus, there is a problem of a higher dose rate
of a charged particle beam resulting in a larger difference between
a dose measured by the dose monitor 54 and a dose of an actual
charged particle beam.
[0068] For example, FIG. 3A illustrates an example that plots a
change in the output of the dose monitor when irradiating a dose
monitor (ionization chamber) with a charged particle beam providing
the same dose while changing only the dose rate I. Although the
same dose monitor is supposed to exhibit the same monitor unit (MU)
ideally in any case of the dose rates I1 to I4, the cases of high
dose rates I3 and I4 are highly affected by ion recombination
described previously, and a lower monitor unit (MU) than the actual
dose will be output from the dose monitor. In particle
radiotherapy, irradiation of the charged particle beam is then
stopped in accordance with the monitor unit (MU) output by the dose
monitor spot by spot. Thus, spots irradiated with the charged
particle beam of the high dose rates I3 and I4 are irradiated with
a more dose of the charged particle beam in an actual treatment
than the dose set by a medical worker, as illustrated in FIG.
3B.
[0069] Since treatment with a high dose rate has been desired for
the purpose of reducing the irradiation time period or the number
of irradiation times to reduce patient burden and the like in
recent years, it is important to correct or compensate a change in
the output of the dose monitor 54 caused by a change in a dose
rate.
[0070] Further, since the amount of information in irradiation
control data of scanning irradiation is significantly large,
generation thereof may take time, and a large capacity of memory of
the irradiation pattern converting device 70 may be required. From
such view points, by using a dose correction factor with respect to
a dose rate acquired in advance for the output change of the dose
monitor in the scanning irradiation and stored in the dose
correction factor storage unit 72, it is possible to perform
correction efficiently and suppress increase in the time required
for generating irradiation control data and memory enhancement of
the irradiation pattern converting device 70.
[0071] Dose correction in the irradiation pattern converting device
70 will be described.
[0072] The treatment plan data generated by the treatment planning
system 60 includes data of doses, dose rates, and the like for
respective spots of a charged particle beam. This treatment plan
data is converted into irradiation control data by the irradiation
pattern converting device 70 (for example, Table 1). The
irradiation control data in Table 1 is data when no correction is
performed on the monitor unit, and irradiation control data
actually generated and transmitted to the irradiation control
device 80 is corrected dose data (for example, Table 3). Further,
corresponding three-dimensional coordinates are allocated to each
spot. For example, the coordinates of spot 1 are (x.sub.1, y.sub.1,
z.sub.1), the coordinates of spot 2 are (x.sub.2, y.sub.2,
z.sub.2), . . . , the coordinates of spot 10000 are (x.sub.10000,
y.sub.10000, z.sub.10000), and so on.
TABLE-US-00001 TABLE 1 Irradiation Control Data Spot position Dose
Dose Spot (coordinates) (MU) rate Energy . . . 1 (x.sub.1, y.sub.1,
z.sub.1) 100 I4 E400 . . . 2 (x.sub.2, y.sub.2, z.sub.2) 120 I1
E400 . . . 3 (x.sub.3, y.sub.3, z.sub.3) 90 I2 E395 . . . . . . . .
. . . . . . . . . . . . . 9999 (x.sub.9999, y.sub.9999, z.sub.9999)
80 I1 E80 . . . 10000 (x.sub.10000, y.sub.10000, z.sub.10000) 70 I3
E70 . . .
[0073] The dose correction factor storage unit 72 stores dose
correction factor data for each dose rate found in advance by
calculation (for example, see Table 2. It is assumed that
I1<I2<I3<I4). A method of finding a dose correction factor
will be described later.
TABLE-US-00002 TABLE 2 Dose Correction Factor Data Dose rate Dose
correction factor R I1 1.00 I2 1.00 I3 0.99 I4 0.98 . . . . . .
[0074] For example, in the example of FIG. 3A and FIG. 3B, while no
dose correction is required for the cases of I1 and I2 with a low
dose rate, the value of monitor unit (MU) output by the dose
monitor 54 results in a small value for the cases of I3 and I4 with
a relatively high dose rate (FIG. 3A), and as a result, the
actually irradiated dose is larger than the planned dose (FIG. 3B).
In the present embodiment, however, when converting a dose of
treatment plan data into irradiation control data, the irradiation
pattern converting device 70 corrects in advance the dose in
treatment plan data with a dose correction factor R in accordance
with a dose rate and generates corrected dose irradiation control
data (for example, Table 3).
TABLE-US-00003 TABLE 3 Corrected Dose (MU) Irradiation Control Data
from Irradiation Control Data of Table 1 Spot position Dose Dose
Spot (coordinates) (MU) rate Energy . . . 1 (x.sub.1, y.sub.1,
z.sub.1) 98 (=100*0.98) I4 E400 . . . 2 (x.sub.2, y.sub.2, z.sub.2)
120 (=120*1.00) I1 E400 . . . 3 (x.sub.3, y.sub.3, z.sub.3) 90
(=90*1.00) I2 E395 . . . . . . . . . . . . . . . . . . . . . 9999
(x.sub.9999, y.sub.9999, z.sub.9999) 80 (=80*1.00) I1 E80 . . .
10000 (x.sub.10000, y.sub.10000, z.sub.10000) 70 (=70*0.99) I3 E70
. . .
[0075] The irradiation pattern converting device 70 generates
irradiation control data while correcting the dose for each spot
described in the treatment plan data by using the dose correction
factor R in accordance with a dose rate. Accordingly, it is
possible to prevent or reduce excessive irradiation of a charged
particle beam due to a difference between a dose actually
irradiated to an irradiation target and a dose measured by the dose
monitor 54.
[0076] Method of Finding Dose Correction Factor
[0077] The dose correction factor storage unit 72 stores data of
dose correction factors R for respective dose rates I derived in
advance. The dose correction factor R for each dose rate I can be
found as follows.
[0078] The ion collection efficiency .eta. in the dose monitor 54
(ionization chamber) is a ratio of ions that can be collected at
the electrode out of ions generated in the ionization chamber, and
.eta.=1 is met in the absence of ion recombination. However, since
all the ions generated in the ionization chamber are not collected
at the electrode in the actual implementation because of ion
recombination, the ion collection efficiency .eta. will be a
smaller value than 1. Thus, the dose correction factor R is
calculated from Equation (1) and (2) below.
R = 1 .eta. ( 1 ) .eta. = z < z max .times. y < y max .times.
F .function. ( y , z ) .times. .eta. i .function. ( y , z ) ( 2 )
##EQU00001##
[0079] Equation (2) will be described here with reference to FIG.
11. FIG. 11 represents the shape of an ionized charge distribution
in the lateral direction (i.e. a direction perpendicular to the
beam traveling direction) generated in the ionization chamber when
the ionization chamber is irradiated with a charged particle beam.
The coordinate in the beam traveling direction is denoted as x, and
the coordinates in directions perpendicular to the beam traveling
direction are denoted as y and z. The function F(y, z) representing
the ionized charge distribution in the lateral direction represents
a Gaussian distribution (Gaussian function). The symbol .eta. of
Equation (2) represents the ion collection efficiency within the
entire region of F(y, z), and .eta..sub.i denotes ion collection
efficiency in one small segment i. The value is calculated for each
small segment i, because the ionized charge amount varies depending
on y and z. Further, the range where .eta..sub.i is integrated is
specified by z.sub.max and y.sub.max. Since the beam size is
represented by a Gaussian distribution a, the ranges of z.sub.max
and y.sub.max vary depending on the size of a (that is, the beam
size).
[0080] The value .eta. is calculated from Equations (3) and (4)
below.
.eta. i .function. ( y , z ) = 1 1 + .xi. i .function. ( y , z ) 2
6 ( 3 ) .xi. .function. ( y , z ) = 2.01 .times. 10 7 .times. ( d 2
.times. q i .function. ( y , z ) V ) ( 4 ) ##EQU00002##
[0081] In Equation (4), d denotes the inter-electrode distance in
the ionization chamber, q.sub.i(y, z) denotes an ionized charge
density in the region i represented by coordinates (y, z), and V
denotes a voltage applied between electrodes in the ionization
chamber. After all, it is indicated that the ionized charge density
q changes depending on the coordinates (y, z). The values
q.sub.i(y, z) are calculated from Equation (5).
q i .function. ( y , z ) = F .function. ( y , z ) .times. I .times.
( dE dx .times. d ) W .times. C v i ( 5 ) ##EQU00003##
[0082] In Equation (5), I denotes the dose rate of a charged
particle beam, dE/dx denotes stopping power per unit length when a
beam passes through the ionization chamber, (where the stopping
power corresponds to energy given to a gas inside the ionization
chamber and depends on beam energy), W denotes a W value of a gas
inside the ionization chamber (where W value is an energy value
required for generating one pair of ionized charges), C denotes an
elementary charge, and v.sub.i denotes a volume of the small
segment i.
[0083] Since the parameters d, V, W, C, and vi in the above
Equations (1) to (5) are constant values in accordance with the
specification in the design of the dose monitor 54, the dose
correction factor R changes in accordance with each parameter of
the dose rate I, dE/dx that depends on the energy, and z.sub.max
and y.sub.max that depend on the beam size.
[0084] In the present embodiment, since the dose correction factor
R is established under the assumption that the dose rate I is a
parameter, the dose correction factor R in accordance with the dose
rate I is calculated by defining the values of dE/dx, which depends
on the energy, and z.sub.max and y.sub.max, which depend on the
beam size, as fixed values (for example, averaged values of the
energy and the beam size available in the charged particle
irradiation apparatus 10). The data of the dose correction factor R
derived in such a way is stored in the dose correction factor
storage unit 72.
[0085] FIG. 4 is a flowchart of particle therapy treatment using
the charged particle irradiation apparatus 10 that performs
scanning irradiation in the present embodiment.
[0086] First, in the treatment planning system 60, a medical worker
specifies a range of a tumor (irradiation target) based on a CT
image and/or an MRI image of a patient secured on a treatment stage
in a treatment room and specifies the shape of the tumor.
Accordingly, the treatment planning system 60 generates treatment
plan data including data of doses and dose rates for respective
spots and transmits the generated treatment plan data to the
irradiation pattern converting device 70 (step S1). The treatment
plan data may include data of energy and beam sizes of a charged
particle beam for respective spots.
[0087] Next, the irradiation pattern converting device 70 selects a
spot in the treatment plan data (step S2) and uses the dose rate I
in the treatment plan data corresponding to the selected spot as a
key to acquire the dose correction factor R corresponding to the
dose rate I from the dose correction factor storage unit 72 (step
S3). The irradiation pattern converting device 70 then corrects a
dose value corresponding to the selected spot by multiplying the
dose value corresponding to the selected spot in the treatment plan
data by the acquired dose correction factor (step S4). Steps S2 to
S4 are repeated until the dose correction for all the spots in the
treatment plan data ends (step S5, No). The corrected dose value
for each spot is temporarily stored in a RAM (not illustrated) of
the irradiation pattern converting device 70 and the like.
[0088] In response to completion of the dose correction for all the
spots, the irradiation pattern converting device 70 generates
irradiation control data based on the treatment plan data (the
corrected dose value stored in advance in the RAM for the dose) and
transmits the generated irradiation control data to the irradiation
control device 80 (step S6). The irradiation control device 80
controls the accelerator 20, the charged particle beam transport
system 30, the focusing magnet 40, and the irradiation nozzle 50 to
control charged particle beam irradiation to the irradiation target
by performing scanning irradiation based on the irradiation control
data received from the irradiation pattern converting device 70,
and irradiation treatment with a charged particle beam to the
irradiation target is started (step S7).
[0089] As described above, in the charged particle irradiation
apparatus 10 that performs scanning irradiation according to the
present embodiment, in response to receiving treatment plan data
including information on a dose and a dose rate for each spot from
the treatment planning system 60, the irradiation pattern
converting device 70 corrects the dose for each spot in treatment
plan data by using data of the dose correction factor R related to
the dose rate I stored in advance in the dose correction factor
storage unit 72 and generates irradiation control data based on the
treatment plan data and the corrected dose value. It is therefore
possible to prevent or reduce, spot by spot, a difference between a
dose actually irradiated and a monitor unit (MU) measured by the
dose monitor 54 in scanning irradiation.
Second Embodiment
[0090] The charged particle irradiation apparatus 10 of a second
embodiment of the present invention is to correct a difference in
dose caused by another influence in addition to the influence due
to ion recombination in the dose monitor 54 (depending on a dose
rate). Herein, another influence may be energy E (parameter dE/dx
in the above equations) and a beam size S (parameters z.sub.max and
y.sub.max in the above equations) of a charged particle beam and a
position of the dose monitor 54 at which a charged particle beam
passes.
[0091] The energy of a charged particle beam depends on the
position in the depth direction of a spot in an irradiation target
as described previously. The beam size of a charged particle beam
depends on the size of one spot. The beam size of a charged
particle beam may be the same or different for respective spots.
Further, the position of the dose monitor 54 (ionization chamber)
at which a charged particle beam passes depends on a spot position
(coordinates).
[0092] First, influence of the energy and the beam size of a
charged particle beam in the dose monitor 54 will be described. As
illustrated in FIG. 5A and FIG. 5B, even with charged particle
beams having the same dose rate (for example, I1), the lower the
energy is (see FIG. 5A, E1<E2<E3) or the smaller the beam
size is (see FIG. 5B, S1<S2<S3), the higher the charge
density ionized in the dose monitor 54 (ionization chamber) will
be. The ionized charge density being high is equal to the fact that
the dose rate is high locally. Thus, the occurrence rate of ion
recombination increases, and this leads to a reduction in the
output of the dose monitor 54 (that is, the dose value measured by
the dose monitor 54 becomes lower than the actual dose). For the
beam size S of a charged particle beam, the beam spread may be
assumed by the Gaussian distribution, and the full width at half
maximum and the like may be used as a reference of the beam
size.
[0093] Further, although a pair of facing electrodes (a high
voltage electrode and a signal electrode) of the dose monitor 54
are ideally planar, respectively, such electrodes may deflect to
some extent such that the distance between the centers of the
electrodes decreases in the actual implementation (FIG. 6A is an XY
plane sectional view of an ionization chamber). Thus, in the dose
monitor 54, the distance of passage between the electrodes varies
in accordance with a position where the charged particle beam
passes. As illustrated in FIG. 6B, the position B is close to the
center of the electrode resulting in the shortest inter-electrode
distance d (=d2) (the passage distance of the charged particle beam
is the shortest), and as the position approaches an electrode
support at the end, the inter-electrode distance d is longer (d2
(position B)<d1 (position A)<d3 (position C). Further, as the
inter-electrode distance d is shorter, even when the same dose is
intended, the output value (MU) of the dose monitor 54 will
indicate a smaller value.
[0094] As described above, with respect to the parameters of a dose
rate, energy, and a beam size of a charged particle beam, the
output of the dose monitor 54 differently changes depending on a
combination of respective parameters. It is required to find in
advance a dose correction factor spot by spot taking the above into
consideration.
[0095] On the other hand, a change in the output of the dose
monitor 54 that depends on the position of the dose monitor 54 at
which a charged particle beam passes (that is, a spot position)
does not depends on the parameters of a dose rate, energy, and a
beam size of a charged particle beam and thus is required to be
considered independently of these parameters. That is, in the
present embodiment, after correction of the energy and the like of
a charged particle beam is completed, correction of the dose is
performed in accordance with the position of the spot.
[0096] Therefore, both a data table of dose correction factors
related to combinations of a dose rate, energy, and a beam size of
a charged particle beam and a data table of dose correction factors
related to spot positions (coordinates) are derived in advance and
stored in the dose correction factor storage unit 72.
[0097] In more details, with respect to generation of the data
table of dose correction factors related to combinations of a dose
rate, energy, and a beam size of a charged particle beam, the dose
correction factor R changes in accordance with each parameter of
the dose rate I, dE/dx that depends on the energy, and z.sub.max
and y.sub.max that depend on the beam size, however, the value of
the energy E, the value of dose rate I, and the value of the beam
size (z.sub.max, y.sub.max) used in the charged particle
irradiation apparatus 10 are within a certain range according to
Equations (1) to (5) described above. For example, in FIG. 7A, when
values that can be taken by the energy E are E1, E2, . . . , E50,
values that can be taken by the dose rate I are I1, I2, . . . ,
I30, and values taken by the beam size S are S1, S2, . . . , S100,
the dose correction factors R are derived in advance from Equations
(1) to (5) and stored in the dose correction factor storage unit 72
for all the combinations of these parameters.
[0098] Further, generation of the data table of dose correction
factors related to spot positions (coordinates) is performed
empirically. That is, in the charged particle irradiation apparatus
10, doses are measured with only the spot position being changed
for the same energy E, spot size S, and dose rate I, and a relative
dose ratio (for example, each monitor unit is divided by the lowest
value of the measured doses) is calculated as the dose correction
factor R and stored in the dose correction factor storage unit 72.
For example, in the example of FIG. 7B, while the energy E, the
spot size S, and the dose rate I of a charged particle beam are
fixed, doses are measured by the dose monitor 54 for respective
spot positions (coordinates (x1, y1, z1) to (xn, yn, zn)) used in
the charged particle irradiation apparatus 10, and relative ratios
of respective doses are calculated as the dose correction factors R
and stored in the dose correction factor storage unit 72.
[0099] FIG. 8 is a flowchart of particle therapy treatment using
the charged particle irradiation apparatus 10 that performs
scanning irradiation in the present embodiment.
[0100] First, in the treatment planning system 60, a medical worker
contours a region of a tumor (irradiation target) based on a CT
image and/or an MRI image of a patient fixed on a treatment stage
in a treatment room and specifies the shape of the tumor.
Accordingly, the treatment planning system 60 generates treatment
plan data including data of doses and dose rates for respective
spots and energy and beam sizes of a charged particle beam and
transmits the generated treatment plan data to the irradiation
pattern converting device 70 (step S11).
[0101] Next, the irradiation pattern converting device 70 selects a
spot in the treatment plan data (step S12). The irradiation pattern
converting device 70 uses the energy E, the dose rate I, and the
beam size S (z.sub.max, y.sub.max) of the charged particle beam in
the treatment plan data corresponding to the selected spot as a key
to acquire a corresponding dose correction factor R1 from the data
table of dose correction factors related to combinations of dose
rates, energy, and beam sizes of a charged particle beam stored in
the dose correction factor storage unit 72 (step S13).
[0102] The irradiation pattern converting device 70 uses spot
positions (coordinates) in the treatment plan data corresponding to
the selected spot as a key to acquire a corresponding dose
correction factor R2 from the data table of dose correction factors
related to the spot positions (coordinates) stored in the dose
correction factor storage unit 72 (step S14).
[0103] The irradiation pattern converting device 70 corrects a dose
value corresponding to the selected spot by multiplying a dose
value corresponding to the selected spot in the treatment plan data
by the dose correction factors R1 and R2 acquired in step S13 and
S14 (step S15). Steps S12 to S15 are repeated until dose correction
for all the spots in the treatment plan data is completed (step
S16, No).
[0104] In response to completion of the dose correction for all the
spots, the irradiation pattern converting device 70 generates
corrected dose irradiation control data and transmits the generated
irradiation control data to the irradiation control device 80 (step
S17). The irradiation control device 80 controls the accelerator
20, the charged particle beam transport system 30, the focusing
magnet 40, and the irradiation nozzle 50 to control charged
particle beam irradiation to the irradiation target by performing
scanning irradiation based on the irradiation control data received
from the irradiation pattern converting device 70, and irradiation
treatment with the charged particle beam to the irradiation target
is started (step S18).
[0105] As described above, in the charged particle irradiation
apparatus 10 that performs scanning irradiation according to the
present embodiment, in response to receiving treatment plan data
including information on energy, a beam size, a dose rate and a
dose of a charged particle beam for each spot from the treatment
planning system 60 and a spot position, the irradiation pattern
converting device 70 corrects the dose for each spot in treatment
plan data by using the dose correction factor data related to the
energy, the beam size, and the dose rate of the charged particle
beam and dose correction factor data related to the spot position
stored in advance in the dose correction factor storage unit 72 and
generates irradiation control data based thereon. It is therefore
possible to effectively prevent or reduce, spot by spot, a
difference between a dose actually irradiated and a dose measured
by the dose monitor 54 in scanning irradiation.
Third Embodiment
[0106] In the charged particle irradiation apparatus 10 of the
third embodiment of the present invention, a second dose monitor 55
inside the irradiation nozzle 50 is further installed in addition
to the first dose monitor 54 (FIG. 9A). The second dose monitor 55
is a backup dose monitor, which is a dose monitor mainly used for
verifying whether or not there is an error in the dose measurement
value of the first dose monitor 54.
[0107] The second dose monitor 55 is placed at the downstream of
the first dose monitor 54 in the traveling direction of a charged
particle beam. Further, in the present embodiment, the charged
particle irradiation apparatus 10 further has a dose monitor
output-correction factor storage unit 74 (FIG. 9B), which corrects
a dose that is measured by the second dose monitor 55 placed at the
downstream for influence of the first dose monitor 54 (mainly,
influence of an energy loss of a charged particle beam) placed at
the upstream. The dose monitor output-correction factor storage
unit 74 may be embedded in the irradiation pattern converting
device 70 or the dose correction factor storage unit 72 or may be
configured as a device separated from both of the above.
[0108] In general, a change in the output of the second dose
monitor 55 due to an energy loss of the charged particle beam in
the first dose monitor 54 increases with a lower irradiation energy
(for example, FIG. 10). Thus, in the present embodiment, the dose
value output by the second dose monitor 55 is corrected by using a
dose monitor output correction factor stored in the dose monitor
output-correction factor storage unit 74 in accordance with the
energy value of a charged particle beam.
[0109] The dose monitor output-correction factor storage unit 74
stores a correction factor used for correcting a dose value
measured by the second dose monitor 55 in accordance with the
energy of a charged particle beam (for example, Table 4).
TABLE-US-00004 TABLE 4 Output Correction Factor Data for Correcting
Output of Dose Monitor Energy Output correction factor E1 0.95 E2
0.98 E3 1.00 E4 1.00 . . . . . .
[0110] As described above, in the present embodiment, by applying
correction of a monitor unit measured by the second dose monitor 55
by using a correction factor stored in the dose monitor
output-correction factor storage unit 74, it is possible to prevent
or reduce a difference between a monitor unit output by the first
dose monitor 54 and a monitor unit output by the second dose
monitor 55.
[0111] The charged particle irradiation apparatus according to one
embodiment of the present invention uses a correction factor
storing a dose correction factor corresponding to a dose rate to
correct a dose for each spot with a dose correction factor and then
performs irradiation of charged particle beam. Therefore, a
difference between a dose actually irradiated to an irradiation
target and a dose measured by a dose monitor is prevented or
reduced.
[0112] The size, the material, the shape, the relative position of
components, and the like described above may be changed in
accordance with the structure of the apparatus to which the present
invention is applied or various conditions. It is not intended to
limit the disclosure to any specific terms used in the description
and the embodiments, those skilled in the art can use another
equivalent component, and the embodiments described above can be
modified and changed differently as long as not departing from the
spirit or the scope of the present invention. Further, even if not
explicitly described, the feature described in association with one
of the embodiments of the present invention can be used together
with another embodiment.
[0113] The present application is based on and claims priority from
Japanese Patent Application No. 2020-104390, filed Jun. 17, 2020,
the disclosure of which is hereby incorporated by reference herein
in its entirety.
LIST OF REFERENCE SYMBOLS
[0114] 10 charged particle irradiation apparatus [0115] 20
accelerator [0116] 30 charged particle beam transport system [0117]
31 charged particle beam adjustment unit [0118] 32 vacuum chamber
[0119] 33 bending magnet [0120] 34 sector-shaped vacuum chamber
[0121] 40 focusing magnet [0122] 50 irradiation nozzle [0123] 52
scanning magnet [0124] 54 dose monitor (first dose monitor) [0125]
55 second dose monitor [0126] 56 position monitor [0127] 60
treatment planning system [0128] 70 irradiation pattern converting
device [0129] 72 dose correction factor storage unit [0130] 74 dose
monitor output-correction factor storage unit [0131] 80 irradiation
control device
* * * * *