WO2020044604A1

WO2020044604A1 - Particle beam accelerator and particle beam therapy system

Info

Publication number: WO2020044604A1
Application number: PCT/JP2019/005847
Authority: WO
Inventors: 知新堀; 隆光羽江; 孝道青木; 孝義関
Original assignee: 株式会社日立製作所
Priority date: 2018-08-31
Filing date: 2019-02-18
Publication date: 2020-03-05
Also published as: JP2020035728A

Abstract

The present invention is provided with: a main magnetic field magnet 1 for generating a static magnetic field; a frequency-variable high-frequency acceleration cavity 1037 for applying a high-frequency electric field for beam acceleration; and a high-frequency kicker 40 for applying a high-frequency electric field having a different frequency from that of the high-frequency acceleration cavity 1037. Concave parts 21a, 21b, 21c, 21d and convex parts 22a, 22b, 22c, 22d are alternately disposed along a beam orbit direction on surfaces of an upper magnetic pole 8 and a lower magnetic pole 9 of the main magnetic field magnet 1 facing an intermediate plane 2, and the high-frequency kicker 40 is disposed in a space between the concave parts 21a.

Description

Particle accelerator and particle beam therapy system

The present invention relates to a particle accelerator and a particle therapy system.

As an example of a synchrocyclotron particle accelerator using a magnetic field flutter, Patent Document 1 discloses a voltage source for sweeping a high frequency voltage in a cavity to accelerate particles from a particle source which is a plasma column, and a particle source in a cavity. It is described that an accelerator is constituted by a magnet moving on an orbit, a regenerator, and a ferromagnetic device arranged in a cavity with a space from the regenerator to eliminate a magnetic field bump formed by the magnet.

JP 2016-213198 A

Recently, the size of particle beam therapy systems used for particle beam therapy has been reduced. Patent Literature 1 discloses a configuration of a particle beam accelerator called a synchrocyclotron used in a particle beam therapy system.

Generally, a particle beam accelerator called a synchrocyclotron is an injection device that includes an ion source, a main magnetic field magnet that generates a main magnetic field for stably circulating the beam, and an acceleration cavity that applies a high-frequency electric field to accelerate the beam in the circumferential direction A gradient magnet for intentionally displacing the beam from the balanced orbit and applying a magnetic field to the beam, and an exit channel for extracting the beam displaced from the balanced orbit outside the accelerator and guiding it to a downstream beam transport system.

機 The mechanism for extracting the beam from the synchrocyclotron is as follows.

First, the beam incident from the ion source orbits, feeling the main magnetic field. The beam is accelerated to a predetermined energy by adjusting the phase of the high-frequency electric field for acceleration so as to match the timing of the orbiting beam passing through the gap of the acceleration cavity. In a synchrocyclotron, the frequency at which the beam circulates varies depending on the energy, so that the frequency of the high-frequency electric field for acceleration needs to be modulated accordingly.

(4) A gradient magnetic field including a quadrupole magnetic field and a hexapole magnetic field is applied to the beam that has reached a predetermined energy. In the synchrocyclotron, the betatron frequency in the beam orbiting plane, that is, the horizontal tune is designed to be around 1 (typically 0.95 or more and less than 1). Increases, and the beam is greatly displaced from the equilibrium trajectory to reach the output channel.

The output channel is a magnet called a septum, and a magnetic field opposite to the main magnetic field is applied to the beam to expand the radius of curvature of the beam and completely depart the beam orbit from the equilibrium orbit.

ビーム The beam that has escaped from the equilibrium orbit jumps out of the accelerator and is guided to the irradiation device via the transport system. Since the energy of the beam extracted in this manner is fixed, the energy is adjusted by reducing the beam energy by passing the beam through a scatterer called a degrader at any stage up to the irradiation device.

調整 However, there is a problem that the adjustment of the beam energy by the degrader inevitably decreases the beam current. A reduction in beam current results in a reduction in dose rate due to a single beam irradiation.

Therefore, it can be said that if the energy can be adjusted without reducing the beam current, the throughput of particle beam therapy using a synchrocyclotron will be improved.

目的 It is an object of the present invention to provide a small energy beam accelerator that does not use a degrader and has variable energy, and a particle beam therapy system including the particle beam accelerator.

The present invention includes a plurality of means for solving the above-mentioned problems. For example, a particle beam accelerator, a main magnetic field magnet for generating a static magnetic field, a frequency modulatable and a beam acceleration A first high-frequency electric field applying device that applies a high-frequency electric field for applying a high-frequency electric field, and a second high-frequency electric field applying device that applies a high-frequency electric field having a frequency different from that of the first high-frequency electric field applying device. A return yoke and a pair of magnetic poles fixed to the return yoke, wherein the pair of magnetic poles are arranged at plane-symmetric positions with respect to an intermediate plane in a space sandwiched between the pair of magnetic poles; On the surface facing the intermediate plane, concave portions and convex portions are alternately arranged along the beam circling direction, and the second high-frequency electric field applying device is arranged in a space sandwiched by the concave portions. That And butterflies.

According to the present invention, it is possible to provide an energy-variable small particle beam accelerator that does not use a degrader. Problems, configurations, and effects other than those described above will be apparent from the following description of the embodiments.

1 is a configuration diagram of a particle beam therapy system according to Embodiment 1 of the present invention. FIG. 2 is a perspective view of a main magnetic field magnet arranged in the accelerator of the particle beam therapy system according to the first embodiment. FIG. 3 is a cross-sectional view of the main magnetic field magnet according to the first embodiment taken along a vertical plane. FIG. 3 is a plan view of the main magnetic field magnet according to the first embodiment as viewed from an intermediate plane. It is sectional drawing by the intermediate plane of the high frequency kicker in Example 1. FIG. 3 is a cross-sectional view of the high-frequency kicker according to the first embodiment, taken along a vertical plane. FIG. 3 is an enlarged plan view of one of the protrusions of the main magnetic field magnet in the first embodiment. FIG. 3 is an enlarged plan view of one of the protrusions of the main magnetic field magnet in the first embodiment. FIG. 3 is an enlarged plan view of one of the protrusions of the main magnetic field magnet in the first embodiment. FIG. 9 is a plan view of a main magnetic field magnet according to a second embodiment of the present invention as viewed from an intermediate plane. FIG. 10 is an enlarged plan view of one of the protrusions of the main magnetic field magnet in the second embodiment. FIG. 10 is an enlarged plan view of one of the protrusions of the main magnetic field magnet in the second embodiment. FIG. 10 is an enlarged plan view of one of the protrusions of the main magnetic field magnet in the second embodiment. FIG. 10 is an enlarged plan view of one of the protrusions of the main magnetic field magnet in the second embodiment. It is sectional drawing by the intermediate plane of the high frequency kicker in Example 2.

First, three major issues to be solved in order to achieve variable energy without using a degrader in a synchrocyclotron type particle beam accelerator will be described.

The first problem is to share the output channel of the beam from low energy to high energy.

ならば If only a few types of energy are extracted, it is considered that a plurality of emission channels can be installed to cope with this. However, taking proton beam therapy as an example, it is desirable to change the energy continuously in the range of approximately 70 MeV to 230 MeV. For this reason, in the case where the beam to be taken out is made continuously variable in energy, it is desired that the output channel be shared rather than providing the output channel for each energy.

The second problem is to reduce the magnetic field required for the septum.

(4) Since the main magnetic field of the synchrocyclotron is constant over time, the radius of curvature is smaller for lower energy beams. Therefore, the magnitude of the magnetic field of the septum required to take it out of the accelerator also increases as the energy becomes lower. The simplest way to reduce the magnetic field that the septum must generate to extract the low energy beam is to lower the main magnetic field, which means an increase in accelerator size. For this reason, the advantage of the synchrocyclotron being small is lost. Therefore, there is a need to reduce the required magnetic field of the septum without increasing the size of the accelerator.

The third problem is to apply a gradient magnetic field selectively to the extracted beam.

In a normal synchrocyclotron, a magnetic field is often used to generate a static gradient magnetic field near the beam path of the maximum energy in order to extract only the beam with the maximum energy.

However, in order to apply a gradient magnetic field to a low-energy beam and extract it, it is necessary to generate a static gradient magnetic field near the low-energy beam, but this is difficult to achieve. This means that if a static multipole magnetic field is generated near the low-energy beam to extract the low-energy beam, the beam will be extracted under the influence of the static gradient magnetic field when the beam reaches its energy. That's why. That is, the beam cannot be accelerated to a higher energy.

Therefore, a structure in which a gradient magnetic field is selectively applied to a beam of any energy from low energy to high energy, for example, in the case of a proton beam therapy system, from 70 MeV to 230 MeV, as needed to extract. I need a way.

Hereinafter, embodiments of a variable energy small particle beam accelerator according to the present invention, which solves these three problems without using the above-described degrader, and a particle beam therapy apparatus including the accelerator will be described with reference to the drawings.

<Example 1>
FIG. 1 is a configuration diagram of the particle beam therapy system according to the first embodiment. FIG. 2 is a perspective view of the main magnetic field magnet arranged in the accelerator. FIG. 3 is a sectional view of the main magnetic field magnet taken along a vertical plane. 4 is a plan view of the main magnetic field magnet viewed from an intermediate plane, FIG. 5 is a cross-sectional view of the high-frequency kicker taken along an intermediate plane, FIG. 6 is a cross-sectional view of the high-frequency kicker taken along a vertical plane, and FIGS. It is the top view which expanded one of the parts.

First, the overall configuration of the particle beam therapy system will be described with reference to FIG.

In FIG. 1, the particle beam therapy system 1001 is installed on the floor of a building (not shown). The particle beam therapy system 1001 includes an ion beam generator 1002, a beam transport system 1013, a rotating gantry 1006, an irradiation device 1007, and a control system 1065.

The ion beam generator 1002 includes an ion source 1003 and an accelerator 1004 to which the ion source 1003 is connected. Details of the accelerator 1004 will be described later.

The beam transport system 1013 has a beam path 1048 reaching the irradiation device 1007, and a plurality of quadrupole electromagnets 1046, a deflection electromagnet 1041, and a plurality of quadrupole electromagnets are provided on the beam path 1048 from the accelerator 1004 toward the irradiation device 1007. 1047, a bending electromagnet 1042,

quadrupole electromagnets

1049 and 1050, and bending

electromagnets

1043 and 1044 are arranged in this order.

A part of the beam path 1048 of the beam transport system 1013 is installed in the rotating gantry 1006, and the bending electromagnet 1042, the

quadrupole electromagnets

1049 and 1050, and the bending

electromagnets

1043 and 1044 are also installed in the rotating gantry 1006. The beam path 1048 is connected to an emission channel 1019 provided in the accelerator 1004.

The rotating gantry 1006 is configured to be rotatable about a rotating shaft 1045, and is a rotating device that rotates the irradiation device 1007 around the rotating shaft 1045.

The irradiation device 1007 includes two

scanning electromagnets

1051 and 1052, a beam position monitor 1053, and a dose monitor 1054. The

scanning electromagnets

1051 and 1052, the beam position monitor 1053, and the dose monitor 1054 are arranged along the central axis of the irradiation device 1007, that is, along the beam axis. The

scanning electromagnets

1051 and 1052, the beam position monitor 1053, and the dose monitor 1054 are arranged in a casing (not shown) of the irradiation device 1007.

The beam position monitor 1053 and the dose monitor 1054 are arranged downstream of the

scanning electromagnets

1051 and 1052. The scanning electromagnet 1051 and the scanning electromagnet 1052 deflect the ion beam, respectively, and scan the ion beam in directions perpendicular to each other on a plane perpendicular to the central axis of the irradiation device 1007. The beam position monitor 1053 measures the passing position of the irradiated beam. The dose monitor 1054 measures the dose of the irradiated beam.

The irradiation device 1007 is attached to the rotating gantry 1006, and is arranged downstream of the bending electromagnet 1044.

治療 On the downstream side of the irradiation device 1007, a treatment table 1055 on which the patient 1056 lies is arranged so as to face the irradiation device 1007.

The control system 1065 includes a central control unit 1066, an accelerator / transport system control unit 1069, a scan control unit 1070, a rotation control unit 1088, and a database 1072.

The central controller 1066 has a central processing unit (CPU) 1067 and a memory 1068 connected to the CPU 1067. The accelerator / transport system controller 1069, the scanning controller 1070, the rotation controller 1088, and the database 1072 are connected to the CPU 1067 in the central controller 1066.

The particle beam therapy system 1001 further has a treatment planning device 1073, and the treatment planning device 1073 is connected to the database 1072. In the particle beam therapy system 1001, the irradiation energy and the irradiation angle of the particle beam are created as a treatment plan by the treatment planning device 1073 prior to the irradiation of the particle beam, and the irradiation is executed based on the treatment plan.

The CPU 1067 of the central controller 1066 reads various operation control programs related to irradiation of each device constituting the particle beam therapy system 1001 from the treatment plan stored in the database 1072, executes the read program, and executes the accelerator. Outputting a command via the transport system control device 1069, the scan control device 1070, and the rotation control device 1088, controls the operation of each device in the particle beam therapy system 1001.

The control processing of the operation to be executed may be integrated into one program, may be divided into a plurality of programs, or may be a combination thereof.

一部 Part or all of the program may be realized by dedicated hardware or may be modularized. Furthermore, various programs may be installed in each device by a program distribution server or an external storage medium.

The control devices may be independent devices connected by a wired or wireless network, or two or more control devices may be integrated.

The beam current measuring device 1098 includes a moving device 1017 and a position detector 1039.

The high-frequency power supply 1036 inputs electric power to the high-frequency acceleration cavity 1037 provided in the accelerator 1004 through the waveguide 1010 and generates a high-frequency electric field for accelerating a beam between the electrode connected to the high-frequency acceleration cavity 1037 and the ground electrode. Excite.

加速 In the accelerator 1004 of this embodiment, it is necessary to modulate the resonance frequency of the high-frequency acceleration cavity 1037 in accordance with the energy of the beam. In order to modulate the frequency, the inductance or the capacitance may be adjusted.

は A known method can be used for adjusting the inductance and the capacitance. For example, when adjusting the capacitance, a high-frequency acceleration cavity 1037 is connected to a variable capacitor for control.

Next, details of the main magnetic field magnet 1 constituting the accelerator 1004 will be described with reference to FIG.

The main magnetic field magnet 1 is a magnet that generates a static magnetic field, and has, as main components, an upper return yoke 4 and a lower return yoke 5 that have a substantially disk shape when viewed from the vertical direction as shown in FIG. are doing.

The upper return yoke 4 and the lower return yoke 5 have a shape that is substantially vertically symmetric with respect to the intermediate plane 2. The intermediate plane 2 substantially passes through the center of the main magnetic field magnet 1 in the vertical direction, and substantially coincides with the orbital plane drawn by the beam being accelerated. The upper return yoke 4 and the lower return yoke 5 have a shape that is perpendicular to the intermediate plane 2 and is generally plane-symmetric with respect to the vertical plane 3 that is a plane passing through the center of the main magnetic field magnet 1 with respect to the intermediate plane 2.

In FIG. 2, an intersecting portion of the intermediate plane 2 with the main magnetic field magnet 1 is indicated by an alternate long and short dash line, and an intersecting portion of the vertical plane 3 with the main magnetic field magnet 1 is indicated by a broken line.

イオン An ion source 1003 is arranged in the upper return yoke 4.

コイル As shown in FIG. 3, a coil 6 is arranged in a space surrounded by the upper return yoke 4 and the lower return yoke 5 symmetrically with respect to the intermediate plane 2.

In the first embodiment, the ion source 1003 is installed outside the main magnetic field magnet 1 assuming an external ion source, and the through-hole 24 is provided in correspondence with the ion source 1003. May be installed inside.

The coil 6 is a superconducting coil, which is installed inside a cryostat (not shown) and is cooled by a refrigerant such as liquid helium or heat transfer from a refrigerator (not shown). The coil 6 is connected to the coil excitation power supply 1057 by the coil extraction wiring 1022 shown in FIG.

真空 A vacuum vessel 7 is provided inside the coil 6 in a space surrounded by the upper return yoke 4 and the lower return yoke 5.

上部 Inside the vacuum vessel 7, an upper magnetic pole 8 is disposed on a surface of the upper return yoke 4 facing the lower return yoke 5. Further, a lower magnetic pole 9 is disposed on a surface of the lower return yoke 5 facing the upper return yoke 4. The upper magnetic pole 8 and the lower magnetic pole 9 are arranged in plane symmetry with respect to the intermediate plane 2.

The upper return yoke 4, the lower return yoke 5, the upper magnetic pole 8, and the lower magnetic pole 9 are made of, for example, pure iron with low impurity concentration, low carbon steel, or the like. The vacuum container 7 is made of stainless steel or the like. The coil 6 is made of a superconducting wire using a superconductor such as niobium titanium.

A space for rotating and accelerating the ion beam is formed between the upper magnetic pole 8 and the lower magnetic pole 9.

The emission channel 1019 includes an electromagnet called a septum, and is connected to the emission channel power supply 1082 shown in FIG. By supplying a current from the power supply for emission channel 1082 to the electromagnet provided in the emission channel 1019, the ion beam that has reached the emission channel 1019 is adjusted and sent to the beam transport system 1013.

FIG. 4 is a plan view of the facing surface 10 as viewed from the intermediate plane 2. Since the main magnetic field magnet 1 has a plane-symmetric structure with respect to the intermediate plane 2, a detailed structure of the main magnetic field magnet 1 will be described below with reference to FIGS.

Concave portions

21a, 21b, 21c, 21d and

convex portions

22a, 22b, 22c, 22d are formed on a surface of the upper magnetic pole 8 and the lower magnetic pole 9 facing the intermediate plane 2, respectively. As shown, the

concave portions

21a, 21b, 21c, 21d and the

convex portions

22a, 22b, 22c, 22d are alternately arranged along the circling direction of the beam orbit 23.

The

concave portions

21a, 21b, 21c, 21d and the

convex portions

22a, 22b, 22c, 22d may be formed integrally with the upper magnetic pole 8 and the lower magnetic pole 9, or may be formed as a separate member and then formed as an upper magnetic pole. At the time of assembly, it may be engaged with the surface of the lower magnetic pole 8 or the lower magnetic pole 9 by a known method such as welding or bolting. The material is desirably the same as the upper magnetic pole 8 and the lower magnetic pole 9.

In addition, as shown in FIG. 4, a gradient magnetic field magnet 31 (peeler), a gradient magnetic field magnet 32 (regenerator), and a high-frequency kicker 40 are provided in the concave portion 21a in which the emission channel 1019 is disposed in the vicinity. .

The

gradient magnets

31 and 32 are coils that generate a gradient magnetic field for displacing the beam trajectory. Among them, the gradient magnetic field magnet 31 is preferably a coil that generates a gradient magnetic field in which the magnetic field distribution of the generated gradient magnetic field decreases in the magnetic field strength radially outward of the accelerator 1004. Further, it is desirable that the gradient magnetic field magnet 32 is a coil that generates a gradient magnetic field in which the magnetic field distribution of the generated gradient magnetic field increases in radial direction and the magnetic field strength increases outward.

The gradient

magnetic field magnets

31 and 32 can be replaced with a structure integrally formed with the concave portion 21a instead of the coil. Examples of such a structure include a structure manufactured as a separate member and then engaged with the concave portion 21a by a known method such as welding or bolting. More specifically, a magnetic substance can be further added to the surface of the concave portion 21a, or the surface shape of the concave portion 21a can be processed.

In the first embodiment, the case where the gradient magnetic field magnet 31 is disposed near the convex portion 22d of the concave portion 21a and the gradient magnetic field magnet 32 is disposed near the convex portion 22a of the concave portion 21a, This position can be reversed.

In addition, since the magnetic field in the region from the outer peripheral surface of the magnetic pole to the inner peripheral surface of the yoke decreases radially outward, the gradient that generates a gradient magnetic field in which the magnetic field intensity decreases radially outward. The magnetic field magnet 31 may be omitted in some cases.

The gradient magnetic field generated by the gradient

magnetic field magnets

31 and 32 desirably includes at least a quadrupole magnetic field component, and desirably includes a multipolar magnetic field having four or more poles or a dipole magnetic field.

The through hole 18 is a through hole for installing the beam transport system 1013. The through hole 19 is provided so as to be symmetric with the through hole 18 with respect to the vertical plane 3 in order to increase the symmetry of the main magnetic field magnet and to increase the accuracy of the magnetic field generated by the main magnetic field magnet. .

FIG. 5 is a sectional view of the high-frequency kicker 40 taken along the intermediate plane 2. FIG. 6 is a sectional view of the high-frequency kicker 40 taken along the vertical plane 3.

The high-frequency kicker 40 shown in FIGS. 2, 5, and 6 is a device for applying a high-frequency electric field having a frequency different from that of the high-frequency accelerating cavity 1037, and is similar to the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32 as shown in FIG. Are arranged in a space interposed between the concave portions 21a.

An emission channel 1019 for extracting a beam accelerated to a predetermined energy out of the accelerator 1004 is provided in a magnetic pole outer peripheral region of the concave portion 21 a provided with the gradient magnetic field magnet 31, the gradient magnetic field magnet 32, and the high frequency kicker 40. .

As shown in FIGS. 5 and 6, the high-frequency kicker 40 includes a ground electrode 41 and a high-voltage electrode 42. The ground electrode 41 is provided on the inner peripheral side, and the high-voltage electrode 42 is provided on the outer peripheral side. As shown in FIGS. 2 and 6, the ground electrode 41 and the high-voltage electrode 42 have shapes substantially parallel to the curve of the beam trajectory so that the high-frequency electric field acts in a direction orthogonal to the beam trajectory in the intermediate plane. Designed for

As shown in FIGS. 5 and 6, a metal projection 43 is attached to the ground electrode 41, so that the concentration of the high-frequency electric field generated between the ground electrode 41 and the high-voltage electrode 42 can be increased.

(6) Since a high-frequency voltage is applied to the high-voltage electrode 42, the high-voltage electrode 42 is supported by the ground electrode 41 via the insulating support 45 as shown in FIG. The ground electrode 41 is supported by the upper magnetic pole 8 and the lower magnetic pole 9 via a non-magnetic support 44.

The ground electrode 41 and the high-voltage electrode 42 are both vertically divided about the intermediate plane 2 through which the beam passes. Although the high-frequency kicker 40 of the present embodiment has a shape with an open end face as shown in FIG. 6, the end face may be closed with a ground electrode except for a beam passage hole to form a resonator structure.

設計 In order to explain the effect of the magnetic pole structure, a design procedure of the main magnetic field magnet 1 will be described with reference to FIGS.

First, in order to determine the size of the main magnetic field magnet 1, it is necessary to determine the magnetic field strength and the radius of the beam orbit at the highest energy. As the magnetic field generated by the main magnetic field magnet 1 is larger, the spread of the beam trajectory becomes smaller, and the accelerator 1004 and, consequently, the particle beam therapy system 1001 can be downsized.

In this example, the magnetic field at the incident point was set to 5 [T], and the beam radius of the highest energy was set to 1 [m]. In this embodiment, the position of the incident point of the beam to be accelerated and the position of the center O1 of the maximum beam energy trajectory are matched.

Next, we need to find the ideal magnetic field distribution in which the beam circulates stably. Therefore, in the present embodiment, the magnetic field is designed based on the principle of weak convergence in order to stably circulate the beam.

加速 In an accelerator using the principle of weak convergence, generally, an amount called an n index as shown in the following equation (1) is used.

Is designed to be larger than 0 and equal to or smaller than 0.2. Here, B is the magnetic field in the intermediate plane 2, ρ is the radius of curvature of the beam orbit, and the magnetic field gradient ∂B / ∂r is perpendicular to the beam traveling direction on the intermediate plane 2 with respect to the direction in which the beam energy increases. The derivative of the magnetic field is shown.

As described above, in this embodiment, since the magnetic field intensity is 5 [T] and the beam radius of the highest energy (maximum orbital radius) is 1 [m], ∂B / ∂r is −1 [T / m]. As described above, the value should be smaller than 0. Here, ∂B / ∂r is -0.5 [T / m]. Then, since the beam radius of the highest energy is 1 [m], the magnetic field on this orbit is 4.5 [T].

円形 Generally, in a circular accelerator that converges a beam based on the principle of weak convergence, the magnetic pole shape is often axially symmetric in order to generate an axially symmetric magnetic field distribution. Then, the magnetic field B becomes a constant value along the beam circling direction. However, the principle of weak convergence does not necessarily require that B is constant in the beam circling direction, and is valid even when B is an average magnetic field in the beam circling direction. That is, the strength of the magnetic field may be distributed in the beam circling direction.

Therefore, in this embodiment, the four

concave portions

21a, 21b, 21c, and 21d and the four

convex portions

22a, 22b, 22c, and 22d distribute the magnetic field in the beam circling direction, and the magnetic field in the beam circulating direction. The average was designed to decrease according to equation (1) with increasing beam energy.

Further, in a region sandwiched between the upper and lower

convex portions

22a, 22b, 22c, and 22d, the distance between the upper magnetic pole 8 and the lower magnetic pole 9 becomes shorter, so that the region is sandwiched between the upper and lower

concave portions

21a, 21b, 21c, and 21d. The magnetic field is larger than in the region that has been set.

Therefore, as shown in FIG. 7, as the beam energy increases and approaches the magnetic pole outer peripheral surface 25, the angular widths θ ₁ , θ of the

convex portions

22a, 22b, 22c, 22d as viewed from the center O1 of the beam orbit. _2,..., it was to θ _n is gradually narrowed _{_{(θ 1> θ 2> θ}} 3>···> θ n) as. In FIG. 7, only the protrusion 22c is shown as a representative. 8 and 9 are the same.

As described above, the narrowing of the angular widths θ ₁ , θ ₂ , θ ₃ ,..., Θ _n of the protruding

portions

22 a, 22 b, 22 c, and 22 d depends on the present embodiment when viewed from the center O 1 of the beam orbit. Means that the angular width of the

concave portions

21a, 21b, 21c, 21d becomes wider as the beam energy increases.

As a first approximation, the magnetic field in the region between the

concave portions

21a, 21b, 21c, and 21d and the magnetic field in the region between the

convex portions

22a, 22b, 22c, and 22d are considered to be constant values, and are determined by Expression (1). Adjustment may be made so that the angular width of the

projections

22a, 22b, 22c, 22d decreases in accordance with the decrease in the average magnetic field.

That is, the

recess

21a, 21b, 21c, a magnetic field _{B v} in region sandwiched 21d, protruding

portions

22a, 22b, 22c, when the magnetic field and _{B h} in a region sandwiched by 22 d, the following formula (2)

May be determined from the relationship. Here, the unit of θ is radian, and _Bv <B (r) < _Bh .

In the

convex portions

22a, 22b, 22c, 22d designed in this way, as shown in FIG. 8, the distances L ₁ , L ₂ ,... In which the accelerated beam passes through one

convex portion

22a, 22b, 22c, 22d. , _{L n} is a turn in a decrease followed by an increase with increasing beam energy _{_{_{(L x> L 2> L}}} 1) (L x> L n) relationship.

Further, as shown in FIG. 9, the

protrusions

22a, 22b, 22c, and 22d have a tangent at a boundary between the protrusion 22c and the recess 21d and a tangent at a boundary between the protrusion 22c and the recess 21c on the opposite side. Are reduced as the beam energy increases (θ ′ ₁ > θ ′ ₂ ). Thereafter, the two tangent lines become parallel, and thereafter, the angle increases.

磁場 The magnetic field obtained in this way can have an average magnetic field for the highest energy beam of 4.5 [T], which is the same value as when the magnetic poles are axisymmetric, so that the size of the accelerator is the same. On the other hand, in the case of the axially symmetric magnetic pole shape, the magnetic field with respect to the beam having the highest energy is uniformly 4.5 [T]. T].

Therefore, by setting the entrance of the emission channel 1019 for taking out the beam accelerated to the predetermined energy to the outside of the accelerator 1004 near the magnetic pole outer peripheral surface 25 of the concave portion 21a, the magnetic field to be generated by the emission channel 1019 for beam extraction is provided. Can be made smaller than the axially symmetric magnetic pole shape, and beam extraction can be facilitated.

Next, the effects of the high-frequency kicker 40, the gradient magnetic field magnet 31, and the gradient magnetic field magnet 32 will be described.

In a synchrocyclotron having the same structure as usual, the beam accelerated to the maximum energy senses the gradient magnetic field generated by the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32, so that a resonance phenomenon occurs in the horizontal movement of the beam, and the beam moves from the equilibrium orbit. Is increased, and the beam reaching the exit channel 1019 is extracted outside the accelerator.

At this time, it is necessary to avoid that the beam having an energy lower than the maximum energy feels the gradient magnetic field formed by the gradient magnetic field magnet 31 or the gradient magnetic field magnet 32 and the orbital motion becomes unstable.

For this reason, the gradient magnetic field generated by the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32 is corrected radially inward of the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32 so that the influence of the gradient magnetic field is sufficiently small inside the beam orbit of the maximum energy. It is desirable to install a magnetic material and a coil (not shown).

Furthermore, in order to extract a low-energy beam, the low-energy beam approaching the extraction energy must be destabilized in the horizontal direction. It is necessary to balance the two of acceleration.

ため Therefore, when extracting a low energy beam, a mechanism for selectively applying a gradient magnetic field, such as applying a gradient magnetic field generated by the gradient

magnetic field magnets

31 and 32 only at that timing, is required. The mechanism for this is the high-frequency kicker 40. The role of the high-frequency kicker 40 is to make the beam to be extracted selectively feel the magnetic field of the gradient

magnetic field magnets

31 and 32.

That is, the beam that is incident and accelerated from the ion source gradually increases its average orbital radius, and finally passes through the inside of the high-frequency kicker 40.

When the beam reaches the desired energy to be extracted, the high-frequency power source 1036 is turned off to cut off the high-frequency electric field excited between the electrode connected to the high-frequency accelerating cavity 1037 and the ground electrode. Turn on.

When the frequency at which the beam reaching the high-frequency kicker 40 orbits the accelerator is f _rev , and the fractional part of the horizontal betatron frequency of the beam is δν, the frequency of the high-frequency kicker 40 is set to be substantially the same as f _rev × δν. Then, a high-frequency electric field of the high-frequency kicker 40 is applied.

As a result, each time the beam trajectory passes through the inside of the high-frequency kicker 40, the beam trajectory receives a radially outward force, and the beam trajectory is gradually shifted radially outward, and finally, the gradient

magnetic field magnets

31 and 32 are generated. It reaches a position where the user can feel the gradient magnetic field.

The beam that has begun to feel the gradient magnetic field of the gradient

magnetic field magnets

31 and 32 begins to diverge in the amplitude of the horizontal betatron motion, and finally reaches the exit channel 1019 and is taken out of the accelerator.

Next, effects of the present embodiment will be described.

In the particle beam therapy system 1001 according to the first embodiment of the present invention, the accelerator 1004 includes a main magnetic field magnet 1 that generates a static magnetic field, and a high-frequency acceleration that can modulate a frequency and applies a high-frequency electric field for accelerating a beam. The main magnetic field magnet 1 includes a cavity 1037 and a high-frequency kicker 40 for applying a high-frequency electric field having a frequency different from that of the high-frequency acceleration cavity 1037. The main magnetic field magnet 1 is fixed to the upper return yoke 4 and the lower return yoke 5. The upper magnetic pole 8 and the lower magnetic pole 9 are arranged at a plane symmetric position with respect to the intermediate plane 2 in a space sandwiched between the upper magnetic pole 8 and the lower magnetic pole 9. On the surface of the upper magnetic pole 8 and the lower magnetic pole 9 facing the intermediate plane 2, the

concave portions

21a, 21b, 21c, 21d and the

convex portions

22a, 22b, 22c, 22d cross along the beam circling direction. Are arranged in the high-frequency kicker 40 is arranged in space between the concave portion 21a.

In the accelerator provided with the high-frequency acceleration cavity 1037 capable of frequency modulation by the high-frequency kicker 40 arranged in the space sandwiched between the recesses 21a, the high-performance and large-sized emission channel 1019 provided only in one is provided. A beam having a predetermined energy can be extracted without arranging a septum electromagnet in which measures such as conversion are taken. Therefore, it is possible to provide a small particle beam accelerator 1004 in which the energy of the extracted beam is continuously variable without using a plurality of emission channels and without using a degrader.

加速 The accelerator 1004 having such a configuration is suitable for a particle beam therapy system which is expected to realize a high irradiation dose rate and improve the treatment throughput of a patient.

Further, since the gradient

magnetic field magnets

31 and 32 for generating a gradient magnetic field for displacing the beam trajectory are arranged in a space between the concave portions 21 a provided with the high frequency kicker 40, the high frequency kicker 40 is displaced. The arrangement can be such that the low-energy beam surely senses the gradient magnetic field. This allows the beam of predetermined energy to reach the emission channel 1019 more efficiently by expanding the horizontal betatron oscillation amplitude in the horizontal direction, and it is possible to extract the beam outside the accelerator.

Further, an emission channel 1019 for extracting a beam accelerated to a predetermined energy to the outside of the accelerator 1004 is provided in a magnetic pole outer peripheral region of the concave portion 21 a provided with the high frequency kicker 40, so that the beam is displaced by the high frequency kicker 40. The beam with the increased horizontal betatron oscillation amplitude can more easily reach the exit channel 1019.

The

convex portions

22a, 22b, 22c, and 22d have a main magnetic field due to the fact that the angular width θ of the

convex portions

22a, 22b, 22c, and 22d as viewed from the center of the beam orbit decreases as the beam energy increases. Is increased, the beam can be accelerated stably without increasing the size of the accelerator. Further, the magnetic field strength in the outer peripheral region of the magnetic pole where the entrance of the exit channel 1019 serving as the exit of the accelerated beam can be reduced. For this reason, it is possible to provide a small accelerator having a main magnetic field magnet from which a beam can be easily extracted without using a difficult method such as high performance and large size of the septum.

Further, when the beam is accelerated to a desired energy, the high-frequency electric field by the high-frequency accelerating cavity 1037 is shut off, and the application of the high-frequency electric field by the high-frequency kicker 40 is started, so that the energy of the beam to be extracted can be selected with high accuracy. it can.

Further, the component of the multipole magnetic field generated by the gradient magnetic field magnet 32 has a magnetic field gradient in which the magnetic field strength increases toward the radially outer side, and the component of the multipole magnetic field generated by the gradient magnetic field magnet 31 Has a magnetic field gradient that reduces the magnetic field strength toward the radially outer side, which can destabilize the betatron oscillation in the orbital plane for the beam with the specific energy to be extracted. Therefore, it is possible to obtain an effect that a beam having an arbitrary energy can be more easily extracted.

<Example 2>
Second Embodiment A particle accelerator and a particle beam therapy system according to a second embodiment of the present invention will be described with reference to FIGS. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 10 is a plan view of the main magnetic field magnet according to the second embodiment viewed from an intermediate plane. 11 to 14 are enlarged plan views of one of the projections of the main magnetic field magnet. FIG. 15 is a cross-sectional view of the high-frequency kicker taken along an intermediate plane.

The particle beam accelerator of the second embodiment is different from the particle beam accelerator of the first embodiment in the shape of the surfaces of the upper magnetic pole and the lower magnetic pole in the main magnetic field magnet. Hereinafter, description will be made with reference to FIG.

In the particle accelerator, if the kinetic energy of the beam is K, the static energy is E ₀ , the speed of light is c, and the number of charges of the charged particles is q, the following equation (3) is obtained.

Holds.

組み合わせる By combining the above equation (3) with the equation (2) described in the first embodiment, θ can be redefined from a function of the radial distance r to a function of the kinetic energy K.

In particular, when the center of the beam orbit coincides with the center of the magnetic pole, r = ρ. However, in the second embodiment, the center of the beam orbit does not coincide with the center of the magnetic pole, and the incident point of the accelerating beam is set. A case is shown in which the position of O2 is different from the center O4 of the maximum beam energy orbit and the centers O3, O5 and O6 of the orbit of the beam of the accelerator.

FIG. 10 is a plan view of the opposing surface 10 according to the second embodiment as viewed from the intermediate plane 2. About the same structure etc. as Example 1, the same number is diverted and pointed out.

In FIG. 10, the beam incident point is O2, the orbital center of the highest energy beam orbit 126 is O4, the orbital center of the intermediate energy beam orbit 127 is O3, and the center of the energy beam orbit accelerated from the middle is O3. Are O5 and O6.

In the second embodiment, the width 128 from the incident point to the beam orbit of the maximum energy is set to 0.1 [m]. Then, assuming that ∂B / －r is -1.0 [T / m] as in the first embodiment, the magnetic field for the highest energy is 4.9 [T].

Also in the second embodiment, as shown in FIG. 11, the angular widths θ _1A , θ _2A , θ _3A ,... Of the convex portion 122c as viewed from the centers O3, O5, O6, O4 of the beam orbit. θ _nA narrows according to the increase of the beam energy according to Expressions (2) and (3) (θ _1A > θ _2A > θ _3A >>...> θ _nA ).

Similarly, as shown in FIG. 12, the angle widths θ _1B , θ _2B ,..., Θ _nB of the convex portion 122d when viewed from the centers O3, O5, and O4 of the beam orbit are expressed by the equations (2) and ( According to 3), the beam energy becomes narrower as the beam energy increases (θ _1B > θ _2B >>...> Θ _nB ).

13, the distance L _1A , L _2A ,..., L _{nA at} which the accelerated beam passes through one convex portion 122c increases as the beam energy increases, as shown in FIG. increase _{_(L 2A>} L _1A) to turn to decrease after the _{_{_{(L 2A> L xA> L}}} nA) relationship.

Further, as shown in FIG. 14, in the convex portion 122c, the angle between the tangent to the boundary between the convex portion 122c and the concave portion 121d and the tangent to the boundary line between the convex portion 122c and the concave portion 121c on the opposite side is a beam. It decreases with increasing energy, after which the two tangents become parallel. Thereafter, the angle becomes larger (θ ′ _3A >>... Θ ′ _nA ).

が Although illustration is omitted, the convex portion 122c and the convex portion 122b symmetrical with respect to the vertical plane 3 are the same as the convex portion 122c. Further, the convex portion 122a having a shape symmetrical to the convex portion 122d and the vertical plane 3 is the same as the convex portion 122d.

In the magnetic field obtained in this way, the average magnetic field along the beam circling direction can be set to the same value as 4.9 [T] when the magnetic poles are axisymmetric, so that the size of the accelerator is axisymmetric. Is equivalent to

On the other hand, in the axially symmetric magnetic pole shape, the magnetic field for the beam with the highest energy is constant at 4.9 [T] along the beam circling direction, but in the second embodiment, 4.9 in the

concave portions

121a, 121b, 121c, and 121d. The magnetic field is less than [T], and the magnetic field exceeds 4.9 [T] in the

convex portions

122a, 122b, 122c, and 122d.

Therefore, also in the second embodiment, the entrance of the emission channel 1019 for taking out the beam accelerated to the predetermined energy to the outside of the accelerator 1004 is set near the magnetic pole outer peripheral surface 125 of the concave portion 121a. Thereby, the magnetic field to be generated by the emission channel 1019 for beam extraction can be made smaller than the axially symmetric magnetic pole shape, and the beam extraction can be facilitated.

Also, the orbital center O4 of the highest energy does not coincide with the incident point O2, and the incident point O2 is shifted toward the beam entrance of the exit channel 1019. When the center of the beam trajectory is shifted in this way, the low-energy beam trajectory approaches the entrance of the emission channel 1019 on the concave portion 121a side, so that a region where the beam trajectory is dense is formed on the emission channel 1019 side.

Therefore, as shown in FIG. 15, the energy band of the beam orbit passing through the high-frequency kicker 40 increases. That is, as compared with the first embodiment, the second embodiment passes through the high-frequency kicker 40 to a lower energy beam orbit.

Therefore, since a high-frequency electric field by the high-frequency kicker 40 can be applied to the lower-energy beam orbit, the lower-energy beam orbit than in the first embodiment can be applied to the gradient magnetic field generated by the gradient

magnetic field magnets

31 and 32. Can be passed nearby.

At this time, since the low energy beam has a smaller radius of curvature than the high energy beam, in order for the low energy beam to feel the gradient magnetic field generated by the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32, the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32 is preferably arranged in a direction in which the beam trajectory is shifted by the high-frequency kicker 40 and is closer to the vertical plane 3.

That is, as described above, similarly to the high-frequency kicker 40, the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32 have the smallest volume of the concave portion 121a in the space between the

concave portions

121a, 121b, 121c, and 121d. It is preferable to arrange them in a space between them.

By arranging the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32 in this way, the low energy beam displaced by the high frequency kicker 40 can surely feel the gradient magnetic field, and the amplitude of the betatron oscillation in the horizontal direction increases. Reaches the emission channel 1019 and can be taken out of the accelerator.

The other configurations and operations are substantially the same as those of the particle accelerator and the particle therapy system according to the first embodiment described above, and the details are omitted.

において The particle beam accelerator and the particle beam therapy system according to the second embodiment of the present invention can provide substantially the same effects as those of the particle beam accelerator and the particle beam therapy system according to the first embodiment.

Further, the space between the concave portions 121a in which the high-frequency kicker 40 and the gradient

magnetic field magnets

31 and 32 are arranged has the smallest volume among the spaces between the

concave portions

121a, 121b, 121c and 121d. A region where the beam orbit becomes dense can be provided on the outer periphery of the magnetic pole where the entrance of the emission channel 1019 is installed. Further, the magnetic field to be generated by the emission channel 1019 for beam extraction can be reduced as compared with the case where the magnetic pole shape is symmetrical with respect to the axis. Therefore, from these effects, it is possible to more easily extract the beam accelerated to the predetermined energy.

<Others>
Note that the present invention is not limited to the above-described embodiment, and includes various modifications. The above embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described above.

In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for a part of the configuration of each embodiment, it is also possible to add / delete / replace another configuration.

For example, in the description of the first and second embodiments, the particles to be accelerated are not specified. That is, regardless of whether protons are supplied from the ion source 1003 or carbon ions are supplied from the ion source 1003, the frequency of the high-frequency accelerating cavity 1037 is adjusted in accordance with each of the accelerating particles to stably rotate the beam. Can be done. The particles to be accelerated are not limited to the protons and carbon ions described above, but may be heavy particle ions other than carbon ions such as helium ions.

In the description of the first and second embodiments, the number of the concave portions and the number of the convex portions provided in the upper magnetic pole 8 and the lower magnetic pole 9 are each four, but the number of the concave portions and the convex portions is not limited to four. If it is an integer of 3 or more, it is possible to generate a magnetic field such that the beam circulates stably.

Although the case where the particle beam therapy system 1001 includes the beam transport system 1013 has been described, the ion beam generator directly connects the ion beam generator and the rotating gantry or the irradiation device without providing the beam transport system. Can be.

Although the case where the rotating gantry 1006 is used as an apparatus for irradiating a particle beam used for treatment has been described, a fixed irradiation apparatus can be used. The number of irradiation devices is not limited to one, and a plurality of irradiation devices can be provided.

In addition, the scanning method using the

scanning electromagnets

1051 and 1052 has been described as an irradiation method. An irradiation method that forms a dose distribution can also be applied to the present invention.

Also, the case where the accelerator is used for particle beam therapy has been described. However, the application of the accelerator is not limited to particle beam therapy, and the accelerator can be used for high energy experiments, PET (Positron Emission Tomography) drug generation, and the like.

DESCRIPTION OF SYMBOLS 1 ... Main magnetic field magnet 2 ... Intermediate plane 3 ... Vertical plane 4 ... Upper return yoke 5 ... Lower return yoke 6 ... Coil 7 ... Vacuum container 8 ... Upper magnetic pole 9 ... Lower

magnetic poles

15, 16, 17, 18, 19, 24 ... Through-hole 20:

Symmetry axes

21a, 21b, 21c, 21d, 121a, 121b, 121c, 121d:

Concave parts

22a, 22b, 22c, 22d, 122a, 122b, 122c, 122d:

Convex parts

23, 126, 127 ...

Beam trajectory

25 , 125 ... magnetic pole outer

peripheral surfaces

31, 32 ... gradient magnetic field magnet 40 ... high frequency kicker (second high frequency electric field applying device)
41 Ground electrode 42 High voltage electrode 43 Projection 44 Nonmagnetic support 45 Insulating support 128 Beam trajectory width 1001 Particle beam therapy system 1004 Accelerator (particle beam accelerator)
1019: emission channel 1037: high-frequency accelerating cavity (first high-frequency electric field applying device)

Claims

A particle accelerator,
A main magnetic field magnet for generating a static magnetic field;
A first high-frequency electric field applying device whose frequency is modulatable and applies a high-frequency electric field for accelerating the beam;
A second high-frequency electric field applying device that applies a high-frequency electric field having a different frequency from the first high-frequency electric field applying device,
The main magnetic field magnet has a return yoke and a pair of magnetic poles fixed to the return yoke,
The pair of magnetic poles is disposed at a plane-symmetric position with respect to an intermediate plane in a space between the pair of magnetic poles,
On the surface of the magnetic pole facing the intermediate plane, concave portions and convex portions are alternately arranged along the beam circling direction,
The particle beam accelerator, wherein the second high-frequency electric field applying device is disposed in a space interposed between the concave portions.
The particle beam accelerator according to claim 1,
A gradient magnetic field magnet for generating a gradient magnetic field for displacing the trajectory of the beam is disposed in a space between the concave portions provided with the second high-frequency electric field applying device. A particle accelerator. .
The particle beam accelerator according to claim 1,
An emission channel for taking out a beam accelerated to a predetermined energy out of the particle beam accelerator is provided in a magnetic pole outer peripheral region of the concave portion provided with the second high-frequency electric field applying device. Line accelerator.
The particle beam accelerator according to claim 2,
The particle beam accelerator, wherein the space between the concave portions in which the second high-frequency electric field applying device and the gradient magnetic field magnet are arranged has the smallest volume among the spaces between the plurality of concave portions.
The particle beam accelerator according to claim 1,
The particle beam accelerator, wherein the angular width of the convex portion as viewed from the center of the beam orbit is narrowed as the beam energy increases.
The particle beam accelerator according to claim 1,
When the beam is accelerated to a desired energy, the high-frequency electric field applied by the first high-frequency electric field applying device is cut off, and the application of the high-frequency electric field by the second high-frequency electric field applying device is started.
The particle beam accelerator according to claim 2,
A component of the multipole magnetic field generated by the gradient magnetic field magnet has a magnetic field gradient in which the intensity of the static magnetic field increases toward a radially outer peripheral side.
The particle beam accelerator according to claim 7,
A component of the multipole magnetic field generated by the gradient magnetic field magnet has a magnetic field gradient in which the intensity of the static magnetic field decreases toward a radially outer peripheral side.
A particle beam therapy system comprising the particle beam accelerator according to claim 1.