WO2018181595A1

WO2018181595A1 - Charged particle beam treatment device

Info

Publication number: WO2018181595A1
Application number: PCT/JP2018/013005
Authority: WO
Inventors: 拓也宮下
Original assignee: 住友重機械工業株式会社
Priority date: 2017-03-31
Filing date: 2018-03-28
Publication date: 2018-10-04
Also published as: TW201836666A; TWI658847B; JP2020096647A

Abstract

This charged particle beam treatment device is provided with: an accelerator which accelerates charged particles and emits a charged particle beam; a radiating unit which uses a scanning method to radiate the charged particle beam toward an object to be irradiated; a collimator which defines a radiation field of the charged particle beam to match the shape of the object to be irradiated; and a control unit which controls the radiating unit. When radiating the charged particle beam at a peripheral edge portion of the radiation field defined by the collimator, the control unit modulates the charged particle beam to have a higher dose than when radiating the charged particle beam at other parts of the radiation field.

Description

Charged particle beam therapy system

The present invention relates to a charged particle beam therapy apparatus.

Conventionally, for example, an apparatus described in Patent Document 1 is known as a charged particle beam treatment apparatus that performs treatment by irradiating an affected area of a patient with a charged particle beam. In the charged particle beam therapy apparatus described in Patent Document 1, a charged particle beam accelerated by an accelerator is irradiated from an irradiation unit by a scanning method. In this charged particle beam therapy apparatus, a part of unnecessary charged particle beams is shielded using a collimator, and then the charged particle beam is irradiated in an irradiation field that matches the shape of the irradiated object.

JP 2014-208307 A

Here, in the charged particle beam therapy system as described above, a part of the charged particle beam irradiated to the peripheral part of the irradiation field is shielded by the collimator, so that the penumbra (cut of dose distribution in the lateral direction) is improved. be able to. On the other hand, shielding the charged particle beam at the periphery of the irradiation field with a collimator reduces the dose at the periphery of the irradiation field, and the flatness of the dose distribution of the charged particle beam with respect to the irradiated object (the dose in the entire irradiation field) There is a problem that the flatness of the distribution is lowered.

Therefore, an object of the present invention is to provide a charged particle beam therapy system capable of achieving both improvement of the penumbra and ensuring flatness of the dose distribution.

In order to solve the above problems, a charged particle beam therapy system according to the present invention includes an accelerator that accelerates charged particles and emits the charged particle beam, and an irradiation unit that irradiates the irradiated object with the charged particle beam by a scanning method. And a collimator that defines the irradiation field of the charged particle beam according to the shape of the irradiated object, and a control unit that controls the irradiation unit, and the control unit charges the peripheral part of the irradiation field defined by the collimator. When irradiating a particle beam, it modulates to the charged particle beam of a higher dose than when irradiating the other part in an irradiation field with a charged particle beam.

In the charged particle beam therapy system according to one embodiment of the present invention, the irradiation field of the charged particle beam irradiated from the irradiation unit to the irradiated object by the scanning method can be defined by a collimator. That is, a part of the charged particle beam irradiated to the peripheral part of the irradiation field can be shielded by the collimator. Thus, the use of a collimator can improve the penumbra (cut of dose distribution in the lateral direction). In addition, when the control unit irradiates the charged particle beam to the periphery of the irradiation field defined by the collimator, it modulates the charged particle beam to a higher dose than when irradiating the other part of the irradiation field with the charged particle beam. To do. Therefore, at the periphery of the irradiation field, the dose of the charged particle beam itself is increased by the modulation, and the flatness of the dose distribution is reduced while the penumbra is improved. The dose distribution can be flattened by shielding the part with a collimator. As described above, it is possible to achieve both improvement of the penumbra and ensuring flatness of the dose distribution.

In the charged particle beam therapy system, the position corresponding to the apex of the dose distribution in the modulated dose distribution of the charged particle beam is set as the first position, and the apex of the dose distribution of the charged particle beam irradiated to the other part When the position corresponding to the same dose is the second position, the collimator is a position on the outer peripheral side of the first position, and the modulated charged particle beam is emitted at a position between the first position and the second position. May be shielded. Thereby, the collimator can shield a part of the charged particle beam modulated at the periphery of the irradiation field at an appropriate position.

According to the present invention, it is possible to provide a charged particle beam therapy system capable of achieving both improvement of the penumbra and ensuring of flatness of the dose distribution.

1 is a schematic configuration diagram of a charged particle beam therapy system according to an embodiment of the present invention. It is a schematic block diagram of the irradiation part vicinity of the charged particle beam therapy apparatus of FIG. It is a figure which shows the layer set with respect to the tumor. It is the figure which looked at the multileaf collimator from the irradiation axis direction. It is a graph which shows the dose distribution of the charged particle beam in the peripheral part vicinity of the irradiation field shown in FIG. It is a graph which shows the dose distribution of the charged particle beam in the peripheral part vicinity of the irradiation field of the charged particle beam therapy apparatus which concerns on a comparative example.

Hereinafter, a charged particle beam therapy system according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

As shown in FIG. 1, a charged particle beam therapy apparatus 1 according to an embodiment of the present invention is an apparatus used for cancer treatment or the like by radiation therapy, and charged particles generated by an ion source (not shown). An accelerator 3 that accelerates and emits a charged particle beam, an irradiation unit 2 that irradiates the irradiated body with the charged particle beam, and a beam transport line 21 that transports the charged particle beam emitted from the accelerator 3 to the irradiation unit 2. It is equipped with. The irradiation unit 2 is attached to a rotating gantry 5 provided so as to surround the treatment table 4. The irradiation unit 2 can be rotated around the treatment table 4 by a rotating gantry 5.

FIG. 2 is a schematic configuration diagram of the vicinity of the irradiation unit of the charged particle beam therapy system of FIG. In the following description, the terms “X-axis direction”, “Y-axis direction”, and “Z-axis direction” will be used. The “Z-axis direction” is a direction in which the base axis AX of the charged particle beam B extends, and is a depth direction of irradiation of the charged particle beam B. The “base axis AX” is an irradiation axis of the charged particle beam B when it is not deflected by a scanning electromagnet 6 described later. FIG. 2 shows a state in which the charged particle beam B is irradiated along the base axis AX. The “X-axis direction” is one direction in a plane orthogonal to the Z-axis direction. The “Y-axis direction” is a direction orthogonal to the X-axis direction in a plane orthogonal to the Z-axis direction.

First, a schematic configuration of the charged particle beam therapy system 1 according to the present embodiment will be described with reference to FIG. The charged particle beam therapy apparatus 1 is an irradiation apparatus according to a scanning method. The scanning method is not particularly limited, and line scanning, raster scanning, spot scanning, or the like may be employed. As shown in FIG. 2, the charged particle beam therapy system 1 includes an accelerator 3, an irradiation unit 2, a beam transport line 21, and a control unit 7.

The accelerator 3 is a device that accelerates charged particles and emits a charged particle beam B having a preset energy. Examples of the accelerator 3 include a cyclotron, a synchrotron, a synchrocyclotron, a linac, and the like. When a cyclotron that emits a charged particle beam B having a predetermined energy is used as the accelerator 3, the energy adjusting unit 20 is used to adjust (decrease) the energy of the charged particle beam sent to the irradiation unit 2. It becomes possible. Since the synchrotron can easily change the energy of the emitted charged particle beam, the energy adjusting unit 20 may be omitted when the synchrotron is used as the accelerator 3. The accelerator 3 is connected to the control unit 7 and the supplied current is controlled. The charged particle beam B generated by the accelerator 3 is transported to the irradiation nozzle 9 by the beam transport line 21. The beam transport line 21 connects the accelerator 3, the energy adjustment unit 20, and the irradiation unit 2, and transports the charged particle beam emitted from the accelerator 3 to the irradiation unit 2.

The irradiation unit 2 irradiates the tumor (irradiated body) 14 in the body of the patient 15 with the charged particle beam B. The charged particle beam B is obtained by accelerating charged particles at high speed, and examples thereof include a proton beam, a heavy particle (heavy ion) beam, and an electron beam. Specifically, the irradiation unit 2 is an apparatus that irradiates the tumor 14 with a charged particle beam B emitted from an accelerator 3 that accelerates charged particles generated by an ion source (not shown) and transported by a beam transport line 21. . The irradiation unit 2 includes a scanning electromagnet 6, a quadrupole electromagnet 8, a profile monitor 11, a dose monitor 12,

position monitors

13a and 13b, a multi-leaf collimator 24, and a degrader 30. The scanning electromagnet 6, the

monitors

11, 12, 13 a, 13 b, the quadrupole electromagnet 8, and the degrader 30 are accommodated in the irradiation nozzle 9. Thus, the irradiation part 2 is comprised by the irradiation nozzle 9 which accommodated each main component in the container. The quadrupole electromagnet 8, the profile monitor 11, the dose monitor 12, the position monitors 13a and 13b, and the degrader 30 may be omitted.

The scanning electromagnet 6 includes an X-axis direction scanning electromagnet 6a and a Y-axis direction scanning electromagnet 6b. The X-axis direction scanning electromagnet 6a and the Y-axis direction scanning electromagnet 6b are each composed of a pair of electromagnets, change the magnetic field between the pair of electromagnets according to the current supplied from the control unit 7, and pass between the electromagnets. The charged particle beam B is scanned. The X-axis direction scanning electromagnet 6a scans the charged particle beam B in the X-axis direction, and the Y-axis direction scanning electromagnet 6b scans the charged particle beam B in the Y-axis direction. These scanning electromagnets 6 are arranged in this order on the base axis AX and downstream of the accelerator 3 from the charged particle beam B.

The quadrupole electromagnet 8 includes an X-axis direction quadrupole electromagnet 8a and a Y-axis direction quadrupole electromagnet 8b. The X-axis direction quadrupole electromagnet 8 a and the Y-axis direction quadrupole electromagnet 8 b converge and focus the charged particle beam B according to the current supplied from the control unit 7. The X-axis direction quadrupole electromagnet 8a converges the charged particle beam B in the X-axis direction, and the Y-axis direction quadrupole electromagnet 8b converges the charged particle beam B in the Y-axis direction. The beam size of the charged particle beam B can be changed by changing the current supplied to the quadrupole electromagnet 8 to change the aperture amount (convergence amount). The quadrupole electromagnet 8 is disposed in this order on the base axis AX and between the accelerator 3 and the scanning electromagnet 6. The beam size is the size of the charged particle beam B on the XY plane. The beam shape is the shape of the charged particle beam B on the XY plane.

The profile monitor 11 detects the beam shape and position of the charged particle beam B for alignment at the time of initial setting. The profile monitor 11 is disposed on the base axis AX and between the quadrupole electromagnet 8 and the scanning electromagnet 6. The dose monitor 12 detects the dose of the charged particle beam B. The dose monitor 12 is disposed downstream of the scanning electromagnet 6 on the base axis AX. The position monitors 13a and 13b detect and monitor the beam shape and position of the charged particle beam B. The position monitors 13 a and 13 b are disposed on the base axis AX and downstream of the charged particle beam B from the dose monitor 12. Each

monitor

11, 12, 13 a, 13 b outputs the detected detection result to the control unit 7.

The degrader 30 finely adjusts the energy of the charged particle beam B by reducing the energy of the charged particle beam B passing therethrough. In the present embodiment, the degrader 30 is provided at the distal end portion 9 a of the irradiation nozzle 9. The tip 9a of the irradiation nozzle 9 is the end on the downstream side of the charged particle beam B.

The multi-leaf collimator 24 defines an irradiation field 60 of the charged particle beam B in a plane direction perpendicular to the irradiation axis direction, and includes shielding

portions

24a and 24b including a plurality of comb teeth. The shielding

portions

24a and 24b are disposed so as to face each other, and an opening 24c is formed between the shielding

portions

24a and 24b. The irradiation field 60 is defined by the opening 24c. The multi-leaf collimator 24 allows the charged particle beam B to pass through the opening 24c, thereby shielding the portion of the charged particle beam B irradiated to the peripheral portion of the irradiation field 60.

Further, the multi-leaf collimator 24 can change the position and shape of the opening 24c, that is, the irradiation field 60, by moving the shielding

portions

24a and 24b back and forth in a direction orthogonal to the Z-axis direction. . Further, the multi-leaf collimator 24 is guided along the irradiation axis direction by the linear guide 28 and is movable along the Z-axis direction. The multi-leaf collimator 24 is disposed on the downstream side of the monitor 4b.

More specifically, as shown in FIG. 4, the multi-leaf collimator 24 has a pair of

leaf groups

31 and 32 that face each other in the X-axis direction. The pair of

leaf groups

31 and 32 face each other in the X-axis direction with the reference axis A in between on the XY plane orthogonal to the reference axis A. The pair of

leaf groups

31 and 32 includes a leaf member 40 that includes a large number of leaves 41 that can advance and retreat independently in the X-axis direction.

The leaf member 40 includes a leaf 41 and a leaf driving unit 43 that moves the leaf 41. The leaf member 40 is disposed along the XY plane so that the leaf 41 of the leaf member 40 included in the leaf group 31 and the leaf 41 of the leaf member 40 included in the leaf group 32 face each other.

The leaf 41 is a rectangular plate-like member extending along the X-axis direction. Since the leaf 41 is a member used to shield the charged particle beam B, the leaf 41 is manufactured from a material capable of shielding the charged particle beam B. Examples of the material capable of shielding the charged particle beam B include brass, copper, tantalum, molybdenum, iron, and the like, but brass or iron is preferable from the viewpoint of good workability and cost.

The leaf drive unit 43 drives each leaf 41 in the X-axis direction based on a signal from the control unit 7 and arranges the leaf 41 at a requested position. The control unit 7 sets the shape of the opening 24c of the multi-leaf collimator 24 according to the shape of the tumor 14 when viewed from the irradiation axis direction. In this embodiment, the charged particle beam B is irradiated by a scanning method. Accordingly, when the multi-leaf collimator 24 performs irradiation of a charged particle beam B to a layer L _n described later, the irradiation field having a shape corresponding to the beam trajectory TL (see FIG. 3B) for the layer L _n . 60 is formed. Details of the operation of the multi-leaf collimator 24 will be described later.

The control unit 7 includes, for example, a CPU, a ROM, a RAM, and the like. The control unit 7 controls the accelerator 3, the scanning electromagnet 6, the quadrupole electromagnet 8, and the multi-leaf collimator 24 based on the detection results output from the

monitors

11, 12, 13a, and 13b.

Further, the control unit 7 of the charged particle beam therapy apparatus 1 is connected to a treatment planning apparatus 100 that performs a treatment plan for charged particle beam therapy. The treatment planning apparatus 100 measures the tumor 14 of the patient 15 by CT or the like before the treatment, and plans a dose distribution (a dose distribution of a charged particle beam to be irradiated) at each position of the tumor 14. Specifically, the treatment planning apparatus 100 creates a treatment plan map for the tumor 14. The treatment planning apparatus 100 transmits the created treatment plan map to the control unit 7.

When performing charged particle beam irradiation by the scanning method, the tumor 14 is virtually divided into a plurality of layers in the Z-axis direction, and the charged particle beam is scanned in one layer so as to follow the scanning path determined in the treatment plan. Irradiate. Then, after the irradiation of the charged particle beam in the one layer is completed, the charged particle beam B is irradiated in the next adjacent layer.

When the charged particle beam treatment apparatus 1 shown in FIG. 2 irradiates the charged particle beam B by the scanning method, the quadrupole electromagnet 8 is turned on (ON) so that the passing charged particle beam B converges.

Subsequently, the charged particle beam B is emitted from the accelerator 3. The emitted charged particle beam B is scanned so as to follow the scanning path determined in the treatment plan by the control of the scanning electromagnet 6. Accordingly, the charged particle beam B is irradiated while being scanned within the irradiation range in one layer set in the Z-axis direction with respect to the tumor 14. Further, the multi-leaf collimator 24 forms an opening 24 c so as to shield a part of the charged particle beam B that is scanning the peripheral portion of the scanning path based on the control signal of the control unit 7. When the irradiation of one layer is completed, the charged particle beam B is irradiated to the next layer.

The charged particle beam irradiation image of the scanning electromagnet 6 according to the control of the control unit 7 will be described with reference to FIGS. 3A shows an irradiation object virtually sliced into a plurality of layers in the depth direction, and FIG. 3B shows a scanning image of a charged particle beam in one layer viewed from the depth direction. , Respectively.

As shown in FIG. 3A, the irradiated object is virtually sliced into a plurality of layers in the irradiation depth direction, and in this example, from the deep layer (the range of the charged particle beam B is long). In order, the layers are virtually sliced into a layer L ₁ , a layer L ₂ ,..., A layer L _n−1 , a layer L _n , a layer L _{n + 1} , a layer L _N−1 , a layer L _N and an N layer. As shown in FIG. 3B, the charged particle beam B follows the beam trajectory TL of the layer L _{n in} the case of continuous irradiation (line scanning or raster scanning) while drawing the beam trajectory TL (scanning path). continuously irradiated Te, in the case of spot scanning is irradiated to a plurality of irradiation spots of the layer L _n. That is, the charged particle beam B emitted from the irradiation nozzle 9 controlled by the control unit 7 moves on the beam trajectory TL.

Next, with reference to FIG.4 and FIG.5, the detail of the control content by the control part 7 is demonstrated. In order to facilitate understanding, and the irradiation field 60 corresponding to the beam trajectory TL layer L _n of the irradiation target in FIG. 4 in a rectangular shape. That is, the

peripheral edge portions

61 and 62 extending in the X-axis direction and the

peripheral edge portions

63 and 64 extending in the Y-axis direction of the irradiation field 60 both extend straight. The

peripheral edge portions

61 and 62 extending in the X-axis direction are defined by side edge portions of the leaf 41 extending in the X-axis direction. The

peripheral edge portions

63 and 64 extending in the Y-axis direction are defined by a plurality of end portions in the X-axis direction of the leaf 41 being arranged in a straight line. In the present embodiment, the beam trajectory TL is configured by combining a plurality of beam lines extending straight in the X-axis direction and beam lines for moving one spot of the charged particle beam B in the Y-axis direction. Shall be.

Specifically, as shown in FIG. 4, the negative end of the beam trajectory TL in the Y-axis direction has an X-axis beam line BLx1 extending along the peripheral edge 61 in the X-axis direction. Further, the beam trajectory TL has an X-axis beam line BLx2 at a position spaced at a predetermined pitch in the Y-axis direction on the positive side in the Y-axis direction with respect to the X-axis beam line BLx1, and further predetermined on the positive side in the Y-axis direction. X-axis beam lines BLx3 are provided at positions separated by a pitch of λ, and thereafter, X-axis beam lines BLxn having the same meaning are provided. The beam trajectory TL has an X-axis beam line BLxN extending in the X-axis direction along the peripheral edge 62 at the positive end in the Y-axis direction.

Further, the beam trajectory TL extends along the peripheral edge 63 from the positive end of the X-axis beam line BLx1 in the X-axis direction toward the positive end of the X-axis beam line BLx2 in the X-axis direction. It has a Y-axis beam line BLy1 extending to the positive side in the axial direction. Further, the beam trajectory TL extends along the peripheral edge 64 from the negative end portion of the X-axis beam line BLx2 in the X-axis direction toward the negative end portion of the X-axis beam line BLx3 in the X-axis direction. It has a Y-axis beam line BLy2 extending to the positive side in the axial direction. The beam trajectory TL has Y-axis beam lines BLy1 and BLy2 having the same meaning at other positions in the Y-axis direction.

When acquiring the beam trajectory TL as described above, the control unit 7 drives the multi-leaf collimator 24 to regulate the shape of the opening 24c in order to define the irradiation field 60 corresponding to the beam trajectory TL. The arrangement is as shown in FIG. And when the control part 7 irradiates the

peripheral part

61,62,63,64 of the irradiation field 60 with the charged particle beam B, it is higher than when irradiating the other part in the irradiation field 60 with the charged particle beam B. Modulate to a dose of charged particle beam B. In the above-described example, “when the charged particle beam is irradiated to the peripheral portion of the irradiation field” means that the charged particle beam B is irradiated to the X axis beam lines BLx1 and BLxN, and the Y axis beam line BLy1. This is when the charged particle beam B is irradiated to BLy2. In the above-mentioned example, “when irradiating a charged particle beam to another part in the irradiation field” means that the charged particle beam B is irradiated from the X-axis beam line BLx2 to the X-axis beam line BLx (N−1). It is time to do. In FIG. 4, only the beam shape of the charged particle beam B irradiated to the

peripheral portions

61, 62, 63, and 64 is shown for easy understanding, but with respect to other beam lines. Also, the charged particle beam B set to a predetermined size and shape is irradiated.

Here, the dose distribution of the charged particle beam B irradiated to the position corresponding to the broken line SL extending in the Y-axis direction as shown in FIG. 4 will be described with reference to FIG. In the dose distribution shown in FIG. 5, the horizontal axis of FIG. 5 indicates the position in the Y-axis direction, and the vertical axis indicates the dose of the charged particle beam B. Further, the dose distribution in FIG. 5 indicates the dose distribution on the upper surface of the multi-leaf collimator 24. However, during the actual operation of the charged particle beam therapy system 1, the dose distribution of the charged particle beam B is acquired at the positions of the

various monitors

12, 13a, 13b. Therefore, the control unit 7 calculates the dose distribution at the position of the multi-leaf collimator 24 based on the detection results of the

various monitors

12, 13a, and 13b, and then controls the multi-leaf collimator 24 and a charged particle beam described later. Control for modulating the dose of B may be performed. Alternatively, the control unit 7 performs a predetermined calculation using the dose distribution at the positions of the

various monitors

12, 13a, and 13b, thereby controlling the multi-leaf collimator 24 and controlling the dose of the charged particle beam B described later. May be done.

In FIG. 5, the dose distribution of the charged particle beam B with respect to the X-axis beam line BLx1 is indicated by “M1”, the dose distribution of the charged particle beam B with respect to the X-axis beam line BLx2 is indicated by “M2”, and the X-axis beam line The dose distribution of the charged particle beam B with respect to BLx3 is indicated by “M3”.

The vertex TP1 of the dose distribution M1 is located at a position P1 on the negative side in the Y-axis direction by a predetermined pitch from the vertex TP2 of the dose distribution M2. Further, the dose ST1 at the vertex TP1 of the dose distribution M1 (that is, the dose peak of the dose distribution M1) is larger than the dose ST2 at the vertex TP2 of the dose distribution M2. The vertex TP3 of the dose distribution M3 is the same distribution as the dose distribution M2 except that the vertex TP3 of the dose distribution M3 is positioned on the positive side in the Y-axis direction by a predetermined pitch from the vertex TP2 of the dose distribution M2. That is, the dose at the apex TP3 of the dose distribution M3 is the dose ST2 as in the dose distribution M2. The dose distribution of the charged particle beam B with respect to the X-axis beam lines after the X-axis beam line BLx3 is a distribution having the same shape as the dose distributions M2 and M3, except that the vertex positions are different.

As described above, the charged particle beam B irradiated to the peripheral portion 61 of the irradiation field 60 (hereinafter sometimes referred to as “modulated charged particle beam”) is different from other parts in the irradiation field 60. Therefore, the dose distribution M1 is modulated to a higher dose than the charged particle beam B (hereinafter sometimes referred to as “normally charged particle beam”), so that the dose distribution M1 is higher than the other dose distributions M2 and M3. The distribution is large and the dose at the peak is large. The magnitude of the dose peak of the modulated charged particle beam B is not particularly limited. For example, the dose peak may be modulated with a magnitude of about 105 to 200% of the peak dose of the charged particle beam B in a normal state. By setting the dose distribution of the charged particle beam B in each beam line as described above, the total dose distribution TM obtained by summing up the individual dose distributions has a local peak before descending in the vicinity of the periphery. (Shown as A in FIGS. 5 and 6).

The arrangement of the multi-leaf collimator 24 with respect to the charged particle beam B that draws the dose distribution as described above will be described. In FIG. 5, in the modulated dose distribution M1 of the charged particle beam B, a position corresponding to the vertex TP1 of the dose distribution M1 is defined as a first position P1. In the dose distribution M1, a position corresponding to the same dose ST2 as the vertices TP2 and TP3 of the dose distributions M2 and M3 of the charged particle beam B irradiated to other portions is set as a second position P2. Note that the second position P2 is set on the positive side and the negative side in the Y-axis direction, but here, the second position P2 indicates a position set on the negative side (that is, on the outer peripheral side). In such a case, the multi-leaf collimator 24 is a charged particle beam modulated at a position on the outer peripheral side from the first position P1 and between the first position P1 and the second position P2. Shield B. That is, when the area between the first position P1 and the second position P2 is the area E1, the side edge of the leaf 41 is disposed at any position in the area E1. When the position of the side edge of the leaf 41 is the position PC, the dose in the region E2 on the negative side of the position PC in the dose distribution TM is shielded. Moreover, the control part 7 adjusts the shape of the opening part 24c of the multileaf collimator 24 so that the leaf 41 may be arrange | positioned in the said position. Alternatively, the control unit 7 may finely adjust the position of the X-axis beam line BLx1 so that the leaf 41 is disposed at the position.

When the dose of the charged particle beam B is modulated, the control unit 7 changes the velocity of the charged particle beam B moving on the X-axis beam line BLx1 to other beams in the case of continuous irradiation (line scanning or raster scanning). It may be slower than the line. As a result, the time during which the charged particle beam B is applied to the X-axis beam line BLx1 is longer than that of the other beam lines, and a large dose distribution can be obtained. In the case of spot scanning, the control unit 7 may modulate the dose of the charged particle beam B by increasing the irradiation time at each irradiation spot set on the X-axis beam line BLx1. In addition, the dose of the charged particle beam B may be modulated by increasing the amount of ions output from the ion source.

In FIG. 5, the dose distribution in the vicinity of the peripheral portion 61 of the irradiation field 60 has been described as an example. However, the same control is performed on the peripheral portion 62. In the vicinity of the

peripheral portions

63 and 64, the control unit 7 determines that the dose of the charged particle beam B with respect to the Y-axis beam lines BLy1 and BLy2 is higher than that of the charged particle beam B with respect to the X-axis beam lines BLx2 to BLx (N−1). Modulate to increase.

Next, functions and effects of the charged particle beam therapy system 1 according to this embodiment will be described.

First, a charged particle beam therapy apparatus according to Comparative Example 1 that does not have a collimator and that does not modulate the dose of the charged particle beam B at the periphery of the irradiation field will be described. In such a charged particle beam therapy system according to Comparative Example 1, as shown in FIG. 6B, the dose distributions M1, M2, and M3 at any irradiation position have the same shape. In this case, the total dose distribution TM draws a graph that gradually decreases near the periphery of the irradiation field. Therefore, there arises a problem that a penumbra (indicated by “T2” in the figure) indicating a break in the dose distribution in the lateral direction becomes large.

In contrast, a charged particle beam therapy apparatus according to Comparative Example 2 will be described in which an irradiation field is defined by a collimator, but the dose of the charged particle beam B is not modulated at the periphery of the irradiation field. In this case, as shown in FIG. 6B, the total dose distribution TM in the region E2 on the outer peripheral side of the position PC of the side edge of the collimator is shielded. As a result, the dose rapidly decreases in the vicinity of the peripheral portion, so that the penampula can be decreased. However, in such a charged particle beam therapy system according to Comparative Example 2, since the dose in the vicinity of the peripheral portion is shielded, the dose distribution with respect to the irradiation field is flattened due to a sudden drop in the dose at the location. The degree may decrease. That is, even after the charged particle beam B is shielded at the collimator position, the charged particle beam B that has passed through the collimator travels to the downstream side and is irradiated onto the tumor layer L _n . At this time, the dose distribution in the vicinity of the periphery of the layer L _n of the irradiation target, by fall due to shielding of the collimator, there is a case where the flatness of the dose distribution is reduced.

Further, as the charged particle beam irradiation apparatus according to Comparative Example 3, an apparatus that modulates the dose of the charged particle beam B at the periphery of the irradiation field without defining the irradiation field with the collimator will be described. In this case, as shown in FIG. 6 (a), the dose distribution M1 with respect to the peripheral portion becomes large, so that the total dose distribution TM rises rapidly in the vicinity of the peripheral portion, thereby reducing the penumbra. (Indicated by “T1” in the figure). On the other hand, the dose distribution TM related to the sum may have a peak (indicated by A in the figure) near the periphery. As a result, the flatness of the dose distribution may decrease due to a locally large dose.

On the other hand, in the charged particle beam therapy apparatus 1 according to this embodiment, the irradiation field 60 of the charged particle beam B irradiated from the irradiation unit 2 to the tumor 14 by the scanning method can be defined by the multi-leaf collimator 24. That is, a part of the charged particle beam B irradiated to the peripheral portion of the irradiation field 60 can be shielded by the collimator. Thus, by using the multi-leaf collimator 24, the penumbra (cut of dose distribution in the lateral direction) can be improved. Furthermore, when the control unit 7 irradiates the charged particle beam B to the peripheral portion of the irradiation field 60 defined by the multi-leaf collimator 24, the control unit 7 irradiates the other part of the irradiation field 60 with the charged particle beam B. Modulate to a high dose of charged particle beam B. Therefore, at the peripheral portion of the irradiation field 60, the dose of the charged particle beam B itself is increased due to the modulation, so that the flatness of the dose distribution is reduced while the penumbra is improved, but the charged particle beam at the peripheral portion of the irradiation field is reduced. The dose distribution can be flattened by shielding a part of B with the multi-leaf collimator 24. As described above, it is possible to achieve both improvement of the penumbra and ensuring flatness of the dose distribution.

In the charged particle beam therapy system 1, in the modulated dose distribution M1 of the charged particle beam B, the position corresponding to the vertex TP1 of the dose distribution M1 is set as the first position P1, and the charged particle beam irradiated to other portions. A position corresponding to the same dose ST2 as the vertices TP2 and TP3 of the dose distributions M2 and M3 of B is defined as a second position P2. In this case, the multi-leaf collimator 24 shields the modulated charged particle beam B at a position on the outer peripheral side from the first position P1 and between the first position P1 and the second position P2. . For example, when the charged particle beam B is shielded on the inner peripheral side from the position P1, the dose at the vertex TP1 of the dose distribution M1 is also shielded. In this case, the effect of modulating the charged particle beam B is reduced. Further, when the charged particle beam B is shielded on the outer peripheral side from the second position P2, the effect of using the multi-leaf collimator 24 is reduced because the amount of the shielded dose is too small. Therefore, by blocking the modulated charged particle beam B at a position between the first position P1 and the second position P2, the effect of modulation of the charged particle beam B and the use of the multi-leaf collimator 24 are achieved. It is possible to achieve both effects. As described above, the multi-leaf collimator 24 can shield a part of the charged particle beam B modulated at the periphery of the irradiation field 60 at an appropriate position.

The present invention is not limited to the embodiment described above.

For example, the shape of the irradiation field shown in FIG. 4 is merely an example, and irradiation fields of any shape may be defined in accordance with the shape of the tumor 14.

Further, the structure of the multi-leaf collimator shown in FIG. 4 is merely an example, and any type of collimator may be adopted as long as the irradiation field can be defined.

In addition, the position where the dose of the charged particle beam is increased by modulating the dose is not limited to the outermost position of the irradiation field, and the doses at a plurality of positions inside the irradiation field may be increased. For example, instead of increasing the dose of only the dose distribution M1 shown in FIG. 5, the dose of the dose distribution M2, for example, may be increased.

DESCRIPTION OF SYMBOLS 1 ... Charged particle beam therapy apparatus, 2 ... Irradiation part, 3 ... Accelerator, 7 ... Control part, 14 ... Tumor (irradiated body), 24 ... Multi-leaf collimator.

Claims

An accelerator that accelerates charged particles and emits charged particle beams;
An irradiating unit for irradiating the charged object with the charged particle beam by a scanning method;
A collimator for defining an irradiation field of the charged particle beam according to the shape of the irradiated object;
A control unit for controlling the irradiation unit,
When the control unit irradiates the charged particle beam to the peripheral portion of the irradiation field defined by the collimator, the control unit has a higher dose than when the other part of the irradiation field is irradiated with the charged particle beam. A charged particle beam therapy device that modulates a charged particle beam.
In the modulated dose distribution of the charged particle beam, the position corresponding to the apex of the dose distribution is the first position, and the dose corresponds to the same dose as the apex of the dose distribution of the charged particle beam irradiated to the other part. When the position to be used is the second position,
The collimator shields the modulated charged particle beam at a position on the outer peripheral side from the first position and between the first position and the second position. The charged particle beam therapy apparatus of description.