Particle beam therapy device

Abstract

The particle beam therapy device is a charged particle beam therapy device that irradiates a patient with a helium ion beam to perform treatment, wherein where another beam, for example, a deuterium beam, that differs in a nuclide from the helium ion beam is generated from a cation beam, a mixed beam in which the helium ion beam and the other beam are mixed is passed through a deflecting magnetic field of a deflecting electromagnet, and then the helium ion beam of the mixed beam is selectively passed by a passage selection unit.

Description

[Technical Field]

[0001] The present invention relates to a particle beam therapy system. [Background technology]

[0002] A conventional technology in this field is a proton beam therapy device described in Patent Document 1. In this type of proton beam therapy device, the spread of the energy of the proton beam is cut by an energy selection system (ESS) that combines, for example, bending electromagnets, quadrupole electromagnets, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-2772 Summary of the Invention [Problem to be solved by the invention]

[0004] In particle therapy systems, beams of other nuclides may be generated from the therapeutic particle beam during transport, and these other beams may be mixed with the therapeutic particle beam. When the other beams are irradiated onto a patient, the other beams may reach a location deeper within the patient's body than the therapeutic beam due to their smaller particle mass numbers, potentially causing unnecessary damage to the location. In view of this problem, the present invention aims to provide a particle therapy system that reduces the amount of unnecessary particle beams irradiated onto the patient. [Means for solving the problem]

[0005] (1) The particle beam therapy device of the present invention is a particle beam therapy device that treats a patient by irradiating the patient with a positive ion beam. When a different type of beam having a different nuclide from the positive ion beam is generated from the positive ion beam, the mixed beam containing the positive ion beam and the different type of beam is passed through a deflection magnetic field, and then the positive ion beam of the mixed beam is selectively passed through a predetermined passage selection section.

[0006] According to this particle beam therapy device, after the mixed beam passes through the deflection magnetic field, the positive ion beam in the mixed beam selectively passes through the pass selection section, so that other types of beams are reduced in the beam sent downstream of the pass selection section.

[0007] (2) The pass selection unit may pass a beam having the same momentum per unit charge as that of the positive ion beam in the mixed beam that has passed through the deflection magnetic field, and may block a beam having a momentum per unit charge different from that of the positive ion beam in the mixed beam.

[0008] In this case, the passing selection section allows the positive ion beam contained in the mixed beam and other types of beams having momentum per unit charge equivalent to that of the positive ion beam to pass through, while blocking other types of beams other than those mentioned above, so that the other types of beams are reduced in the beam sent downstream of the passing selection section.

[0009] (3) The deflection magnetic field may vary the trajectories of the beams contained in the mixed beam upstream of the pass selection section depending on the momentum per unit charge, and the pass selection section may pass the beams contained in the mixed beam at positions on the trajectory corresponding to the momentum per unit charge of the positive ion beams contained in the mixed beam, and may shield the beams contained in the mixed beam at positions other than the positions on the trajectory corresponding to the momentum per unit charge of the positive ion beams contained in the mixed beam.

[0010] In this case, the trajectories of the beams contained in the mixed beam differ depending on the momentum per unit charge after passing through the deflection magnetic field. Then, the passing selection section allows the positive ion beam and other beams having the same momentum per unit charge as the positive ion beam to pass through, while blocking other beams, so that the other beams are reduced in the beam sent downstream of the passing selection section.

[0011] (4) The positive ion beam may be a helium ion beam, and the other beams may include a deuterium ion beam, thereby obtaining a helium ray therapy device in which the other beams irradiated to the patient are reduced.

[0012] (5) The particle beam therapy device of the present invention may include a degrader that is provided upstream of the deflection magnetic field and reduces the energy of the positive ion beam. In such a degrader, when the energy of the positive ion beam is reduced, other types of beams having nuclei different from those of the positive ion beam are likely to be generated. These other types of beams are reduced by the deflection magnetic field and the pass selection unit as described above.

[0013] (6) The degrader may be provided within the gantry, and the deflection magnetic field and the pass selector may also be provided within the gantry. By providing the degrader, the deflection magnetic field, and the pass selector within the gantry, the beam transport system upstream of the gantry can be shortened, which in turn allows for the miniaturization of the particle beam therapy device.

[0014] (7) The particle beam therapy device of the present invention is a particle beam therapy device that treats a patient by irradiating the patient with a positive ion beam, and includes: a cyclotron that emits a positive ion beam; a degrader that is located downstream of the cyclotron and that reduces the energy of the positive ion beam and generates from the positive ion beam a beam of another type having a nuclide different from that of the positive ion beam when the energy is reduced; a bending electromagnet that is located downstream of the degrader and that deflects a mixed beam that is a mixture of a positive ion beam and another type of beam so that the trajectories of the beams contained in the mixed beam vary according to the momentum per unit charge; and a pass selection unit that is located downstream of the bending electromagnet and that allows the beams contained in the mixed beam to pass at the position of the trajectory of the positive ion beam in the mixed beam and blocks the beams contained in the mixed beam at positions other than the position of the trajectory of the positive ion beam in the mixed beam.

[0015] In this particle beam therapy system, due to the nature of the cyclotron, a positive ion beam with a fixed energy is emitted from the cyclotron. By reducing the energy of this positive ion beam using a degrader, the positive ion beam can be adjusted to an energy suitable for treatment. In the degrader, other types of beams with different nuclides are generated from the positive ion beam, and a mixed beam containing the positive ion beam and other types of beams is sent downstream of the degrader. This mixed beam is deflected by a bending electromagnet, and downstream of the bending electromagnet, the trajectories of each beam contained in the mixed beam differ depending on the momentum per unit charge.

[0016] The pass selector then passes the beam contained in the mixed beam at the orbital position of the positive ion beam in the mixed beam. Here, due to the nature of the cyclotron, the positive ion beam extracted from the cyclotron exhibits a biased energy distribution for a single nuclide. Therefore, the momentum per unit charge of the positive ion beam after its energy reduction by the degrader is relatively biased. Therefore, by targeting the orbital position corresponding to the momentum per unit charge of the positive ion beam, the pass selector can be set to pass most of the positive ion beam contained in the mixed beam. On the other hand, since the other-species beam is generated when the energy of the positive ion beam is reduced by the degrader, the variation in momentum per unit charge is greater than that of the positive ion beam derived from the cyclotron. Furthermore, as described above, the region in which the momentum per unit charge of the positive ion beam after its energy reduction is biased is considered to be relatively narrow, so the range of momentum per unit charge of the beam to be passed by the pass selector can be relatively narrow. Therefore, even if some of the other types of beams have momentum per unit charge equivalent to that of the positive ion beam, they pass through the pass selector, but the amount is kept small and most of the other types of beams are blocked by the pass selector, resulting in a reduction of the other types of beams from the positive ion beam irradiated onto the patient downstream of the pass selector. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a particle beam therapy system that reduces unnecessary particle beams irradiated onto a patient. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a plan view of the particle beam therapy system according to the first embodiment. FIG. [Figure 2](a) is a graph showing a schematic diagram of the momentum distribution per unit charge of a helium ion beam extracted from an accelerator, and (b) is a graph showing a schematic diagram of the momentum distribution per unit charge of a decompressed helium ion beam and the momentum distribution per unit charge of other beams, superimposed on each other. [Figure 3] 10(a) and 10(b) are perspective views, partly cut away, that schematically show the vicinity of the passage selection section of each example. [Figure 4] FIG. 2 is an enlarged view showing the vicinity of a beam selection unit. [Figure 5] FIG. 4 is an enlarged plan view of a main part of a particle beam therapy system according to a second embodiment. [Figure 6] FIG. 10 is an enlarged plan view of a main part of a particle beam therapy system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] A preferred embodiment of a particle beam therapy system according to the present invention will be described below with reference to the drawings. In the description of the drawings, identical elements are designated by the same reference numerals, and duplicated explanations will be omitted. The particle beam therapy system 1 of this embodiment is applied to, for example, cancer treatment, and is a charged particle beam therapy system that treats tumors in a patient's body by irradiating them with helium ion beams (α rays), which are a type of positive ion beam.

[0020] Fig. 1 is a plan view of the layout of a particle beam therapy system 1. As shown in Fig. 1, the particle beam therapy system 1 includes an accelerator 3 that emits a helium ion beam, an irradiation unit 9 that irradiates a patient 7 on a treatment table 5 with the helium ion beam, and a transport unit 11 that transports the helium ion beam extracted from the accelerator 3 to the irradiation unit 9. The particle beam therapy system 1 is installed in, for example, a one-story building 13.

[0021] The accelerator 3 accelerates helium nuclei (α particles) and emits a helium ion beam. In this embodiment, the accelerator 3 is a cyclotron (e.g., a superconducting cyclotron). The irradiation unit 9 is mounted on a rotatable gantry 15. The gantry 15 is provided to surround the treatment couch 5 and is rotatable within the building 13 about a predetermined rotation axis H near the treatment couch 5. The irradiation unit 9 is rotatable around the patient 7 on the treatment couch 5 as the gantry 15 rotates, and is able to irradiate the patient 7 with the helium ion beam from various directions. The irradiation unit 9 also includes, for example, a scanning magnet and a multi-leaf collimator (not shown), and irradiates the tumor in the patient 7 with the helium ion beam while scanning it.

[0022] Next, the transport unit 11 will be described. Hereinafter, the upstream / downstream direction of the helium ion beam in the transport unit 11 is referred to as the Z direction, a direction perpendicular to the Z direction is referred to as the X direction, and a direction perpendicular to both the Z direction and the X direction is referred to as the Y direction. In the state shown in FIG. 1 , the direction perpendicular to the plane of the paper in FIG. 1 is referred to as the Y direction in each part of the transport unit 11. The transport unit 11 includes a beam duct 17 and a number of bending electromagnets 21 and quadrupole electromagnets 23 arranged along the beam duct 17. The bending electromagnets 21 are, for example, normal-conducting electromagnets. The transport unit 11 includes an external path 11A that transports the helium ion beam from the accelerator 3 to the entrance 15 a of the gantry 15, and an internal path 11B that is provided in the gantry 15 and transports the helium ion beam from the entrance 15 a of the gantry 15 to the irradiation unit 9. The external path 11A is fixed to the building 13, and the internal path 11B rotates as a whole around the rotation axis H as the gantry 15 rotates.

[0023] The beam duct 17 is a vacuum duct through which the helium ion beam passes. The bending electromagnet 21 forms a bending magnetic field in the Y direction within the beam duct 17, thereby bending the traveling direction of the helium ion beam in the X direction. By providing such a bending electromagnet 21, the transport path of the helium ion beam can be curved at a desired position within the building 13, and the transport section 11 can be shaped as desired. The quadrupole electromagnet 23 includes an electromagnet that focuses the helium ion beam in the X direction and an electromagnet that focuses the helium ion beam in the Y direction. The quadrupole electromagnet 23 focuses the helium ion beam during transport by the transport section 11, adjusting the beam shape.

[0024] The accelerator 3 of the particle beam therapy system 1 emits a helium ion beam with a fixed energy due to the nature of a cyclotron, and the energy of the helium ion beam cannot be adjusted. For this reason, the particle beam therapy system 1 is equipped with a degrader 27 provided in the beam duct 17 of the external path 11A. The degrader 27 is provided in a portion of the external path 11A that extends linearly downstream from the accelerator 3. In other words, the degrader 27 is located further upstream than the bending electromagnet 21, which is located most upstream of the transport section 11.

[0025] The degrader 27 has, for example, a plate-shaped attenuating material made of a predetermined material (for example, graphite or beryllium). In the degrader 27, the helium ion beam passes through the attenuating material, thereby reducing the energy of the helium ion beam. In this way, by reducing the energy of the helium ion beam by the degrader 27, the energy of the helium ion beam sent to the irradiation unit 9 is adjusted to be suitable for treating the patient 7. Note that a collimator (not shown) is installed immediately downstream of the attenuating material of the degrader 27 to cut off the beam that deviates from the aperture of the transport unit 11.

[0026] In the degrader 27, as the helium ion beam passes through the damping material, some helium nuclei decay, generating particle beams of other nuclides such as deuterium, tritium, neutrons, helium-3, and hydrogen, generating a deuterium ion beam, a tritium ion beam, a neutron ion beam, a helium-3 ion beam, a hydrogen ion beam, etc. Then, a beam (hereinafter referred to as a "mixed beam") that is a mixture of the helium ion beam used for treatment and the beams of the above-mentioned other nuclides that are not required for treatment (hereinafter referred to as "other beams") is transported downstream from the degrader 27.

[0027] Fig. 2(a) is a graph schematically showing the momentum distribution F per unit charge of the helium ion beam extracted from the accelerator 3. Fig. 2(b) is a graph schematically showing the momentum distribution Fj per unit charge of the helium ion beam that has passed through the degrader 27 and the momentum distribution Fk per unit charge of the other type of beam generated by the degrader 27, superimposed on each other.

[0028] Due to the nature of the cyclotron, which emits a particle beam of a single nuclide biased toward a predetermined energy, the momentum distribution per unit charge of the helium ion beam extracted from the accelerator 3 shows a sharp peak at E0. In this way, the momentum per unit charge of the helium ion beam extracted from the accelerator 3 is E0, whereas the momentum per unit charge of the helium ion beam corresponding to the energy suitable for treating the patient 7 is assumed to be E1 to E2 (however, E2 <E0)。

[0029] As shown in Figures 2(a) and 2(b), the momentum per unit charge of the helium ion beam is reduced from E0 to E1 to E2 by passing through the degrader 27. As shown in Figure 2(b), the distribution of the momentum per unit charge of the helium ion beam after the reduction shows a gentler peak than before the reduction, but is still distributed in a relatively narrow range from E1 to E2. On the other hand, as shown in Figure 2(b), the momentum per unit charge of the other beams generated by the degrader 27 varies greatly and is distributed in a wide range spanning E1 to E2.

[0030] Here, the particle beam irradiated onto the patient 7 has a range within the body of the patient 7 that varies depending on the mass number, valence, and velocity of the particle. That is, the range of a heavy charged particle is approximately: (A / Q 2 )×v 4 (where A is the mass number, Q is the valence, and v is the velocity) Therefore, if the patient 7 is irradiated with a different type of beam having a different mass number, valence, and velocity from that of helium nuclei, there is a high possibility that unnecessary damage will be caused to areas in front of or behind the tumor. Therefore, it is desirable that the different type of beam generated by the degrader 27 as described above be removed as much as possible before reaching the patient 7.

[0031] Therefore, as shown in FIG. 1, the particle beam therapy device 1 includes a beam selector 31 provided in the transport unit 11 downstream of the degrader 27. The beam selector 31 selectively shields other beams from the mixed beam transported downstream from the degrader 27 and selectively passes the helium ion beam used for treatment. "Selectively passing" the helium ion beam does not mean that no beams other than the helium ion beam are allowed to pass, but rather means that the helium ion beam is relatively easily passed and other beams are relatively difficult to pass. Similarly, "selectively shielding" other beams does not mean that no beams other than the other beam are blocked, but rather means that the other beams are relatively easily blocked and other beams are relatively difficult to block.

[0032] Specifically, the beam selection unit 31 has one bending electromagnet 21A, which is arranged downstream of the degrader 27 among the bending electromagnets 21 of the transport unit 11, and a passage selection unit 33, which is arranged further downstream of the bending electromagnet 21A. The bending electromagnet 21A constituting the beam selection unit 31 is the bending electromagnet 21 through which the mixed beam generated in the degrader 27 first passes. In other words, although a quadrupole electromagnet 23 may be arranged between the degrader 27 and the bending electromagnet 21A, no other bending electromagnets 21 are arranged.

[0033] The pass selection unit 33 is, for example, a member that opens a part of the cross section of the beam duct 17 in the X direction and allows the beam to pass through the opening. The pass selection unit 33 is arranged upstream of the bending electromagnet 21 that is arranged next downstream of the bending electromagnet 21A. In other words, although a quadrupole electromagnet 23 may be arranged between the bending electromagnet 21A that constitutes the beam selection unit 31 and the pass selection unit 33, no other bending electromagnets 21 are arranged. In the example of FIG. 1, neither the quadrupole electromagnet 23 nor the other bending electromagnets 21 are arranged between the bending electromagnet 21A and the pass selection unit 33.

[0034] 3(a) and (b) are perspective views, partly cut away, that schematically show the vicinity of the pass selection section 33. As the pass selection section 33, for example, a slit member 33A, an example of which is shown in FIG. 3(a), may be used. In the slit member 33A, a slit that is opened to pass the beam is formed as a beam passing section 35 in a partial range in the X direction of the cross section of the beam duct 17. Furthermore, a beam blocking section 37 that blocks the beam by causing it to collide is formed in a position other than the beam passing section 35.

[0035] FIG. 4 is an enlarged view of the vicinity of the beam selector 31. In the beam selector 31, as shown in FIG. 4, the traveling direction of the mixed beam 101 is curved by a Y-direction deflection magnetic field AY formed in the beam duct 17 by the deflection electromagnet 21A. The radius of curvature of the curvature of each beam included in the mixed beam 101 depends on the momentum per unit charge of the beam. The higher the momentum per unit charge of the beam, the larger the radius of curvature. The lower the momentum per unit charge of the beam, the smaller the radius of curvature. As a result, the trajectories of each beam included in the mixed beam 101 differ depending on the momentum per unit charge. At the position of the slit member 33A, the passing position in the X direction of each beam differs depending on the momentum per unit charge. Of the mixed beam 101, only beams having momentum per unit charge E1 to E2 pass through the beam passing section 35, for example, on trajectory 103, and are transported downstream. Of the mixed beam 101, a beam having a momentum per unit charge less than E1 or more than E2 is transported, for example, in an orbit 105, collides with the beam shielding portion 37, and is shielded.

[0036] As a result, most of the helium ion beams contained in the mixed beam pass through the pass selector 33, and most of the other beams except for those having momentum per unit charge of E1 to E2 are blocked by the pass selector 33. That is, the pass selector 33 selectively passes the helium ion beams used for treatment out of the mixed beam, and the beam selector 31 selectively passes the helium ion beams used for treatment out of the mixed beam.

[0037] As the pass selector 33, a collimator 33B, an example of which is shown in FIG. 3(b), may be used instead of the slit member 33A. The beam passing section 35 in this collimator 33B is configured with an opening provided near the center of the cross section of the beam duct 17, instead of the above-mentioned slit. This opening is circular in the example of FIG. 3(b), but may also be rectangular. A pass selector 33 employing such a collimator 33B also selectively passes the helium ion beam out of the mixed beam.

[0038] Next, the effects of the particle beam therapy system 1 will be described. In the particle beam therapy system 1, due to the nature of the cyclotron, a fixed-energy helium ion beam is emitted from the accelerator 3. By reducing the energy of this helium ion beam by the degrader 27, the helium ion beam can be adjusted to an energy suitable for treatment. Thereafter, when the mixed beam transported downstream from the degrader 27 is deflected by the bending electromagnet 21A and its trajectory is curved, the curvature of the curve differs depending on the momentum per unit charge of the beam, so that downstream of the bending electromagnet 21A, the trajectories of the individual beams included in the mixed beam differ in the X direction depending on the momentum per unit charge.

[0039] Thereafter, the passing selection unit 33 passes the beam contained in the mixed beam at the position of the trajectory of the helium ion beam in the mixed beam. Here, due to the properties of the cyclotron, the helium ion beam extracted from the accelerator 3 exhibits a momentum distribution per unit charge biased toward E0, and therefore the helium ion beam after its energy reduction by the degrader 27 also exhibits a momentum distribution per unit charge relatively biased toward E1 to E2. Therefore, by providing the beam passing unit 35 aiming at the trajectory position corresponding to the momentum range E1 to E2 per unit charge of the helium ion beam (the position of the trajectory 103 in FIG. 4), it becomes possible to set the passing selection unit 33 to pass most of the helium ion beam contained in the mixed beam.

[0040] On the other hand, since the other-type beam is accidentally generated by the collision of the helium ion beam with the degrader 27, the momentum per unit charge varies more significantly than the helium ion beam derived from the cyclotron. Furthermore, as described above, the range E1 to E2 in which the momentum per unit charge of the helium ion beam is biased is relatively narrow, so the beam passing section 35 can be made relatively narrow. Therefore, even if some of the other-type beams have momentum per unit charge E1 to E2 equivalent to that of the helium ion beam pass through the beam passing section 35, their amount is kept small, and most of the other other-type beams are blocked by the beam blocking section 37. As a result, the other-type beams are reduced from the helium ion beam sent downstream of the pass selector 33. Therefore, the other-type beams irradiated to the patient 7 are reduced, reducing unnecessary damage to areas other than the tumor. Furthermore, the activation and malfunction of the various components of the transport section 11 due to the other-type beams are also reduced.

[0041] Second Embodiment In this embodiment, components identical or equivalent to those in the first embodiment are designated by the same reference numerals, and redundant description will be omitted. In the particle beam therapy system of this embodiment, as shown in FIG. 5 , a degrader 27 is provided immediately upstream of the entrance 15a of the gantry 15. A beam selector 31 is constructed in the internal path 11B within the gantry 15. The beam selector 31 includes one bending electromagnet 21B within the gantry 15 and a pass selector 33 disposed downstream of the bending electromagnet 21B. In this configuration in which the beam selector 31 is provided within the gantry 15, it is not necessary to provide a bending electromagnet 21 in the external path 11A extending from the accelerator 3 to the entrance 15a of the gantry 15. Therefore, the external path 11A can be made straight and can be shortened. Furthermore, shortening the external path 11A enables the particle beam therapy system to be miniaturized as a whole.

[0042] Third Embodiment In this embodiment, components that are the same as or equivalent to those in the first or second embodiment are assigned the same reference numerals, and redundant description will be omitted. In the particle beam therapy system of this embodiment, as shown in FIG. 6 , a degrader 27 is provided in the internal path 11B within the gantry 15. The degrader 27 is provided immediately downstream of the entrance 15a of the gantry 15. A beam selector 31 is constructed downstream of the degrader 27 in the internal path 11B within the gantry 15. The beam selector 31 includes one bending electromagnet 21B within the gantry 15 and a passage selector 33 disposed downstream of the bending electromagnet 21B. Compared to the second embodiment, in this configuration in which the degrader 27 is provided within the gantry 15, the external path 11A can be further shortened, thereby enabling further miniaturization of the particle beam therapy system as a whole.

[0043] The present invention can be embodied in various forms, including the above-described embodiments, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, it is also possible to create modified examples by utilizing the technical matters described in the above-described embodiments. The configurations of the embodiments may be used in appropriate combinations. For example, in the beam selector 31, the passage selector 33, which is composed of a slit member 33A or a collimator 33B, may be installed within the deflection magnetic field AY formed by the deflection electromagnet 21A, rather than downstream of the deflection electromagnet 21A.

[0044] Furthermore, the present invention is not limited to helium ion beam therapy devices and can be applied to various particle beam therapy devices. In particular, the present invention is preferably applicable to cases where particles of a particle beam used for therapy may decay when passing through the degrader 27, generating other beams. Considering a proton beam therapy device using a proton beam for therapy, the protons cannot become smaller particles when their energy is reduced by the degrader 27, and other beams cannot be generated. Therefore, the present invention is preferably applicable to particle beam therapy devices that use particle beams other than proton beams for therapy. Examples of such particle beams include helium ion beams and carbon ion beams (carbon beams). When a carbon ion beam passes through the degrader 27, other beams such as a hydrogen ion beam, a deuterium ion beam, and a helium ion beam are generated. However, these other beams irradiated to the patient 7 can be reduced by the beam selector 31. [Explanation of symbols]

[0045] 1...particle beam therapy device, 3...accelerator (cyclotron), 15...gantry, 21, 21A, 21B...bending electromagnet, 27...degrader, 33...passing selection section, 35...beam passing section, 37...beam shielding section, 103...trajectory (trajectory corresponding to the momentum per unit charge of the positive ion beam), AY...bending magnetic field.

Claims

1. A particle beam therapy device that treats a patient by irradiating the patient with a positive ion beam, which is a helium ion beam or a carbon ion beam, comprising: a degrader provided upstream of the deflection magnetic field to reduce the energy of the positive ion beam; a pass selection unit that is provided downstream of the deflection magnetic field and that selectively passes the positive ion beam out of a mixed beam that is a mixture of the positive ion beam and a beam of another type whose nuclide is different from that of the positive ion beam generated by the positive ion beam passing through the degrader.

2. The deflection magnetic field causes the trajectories of the beams included in the mixed beam upstream of the pass selection section to differ in a first direction perpendicular to the upstream and downstream directions of the mixed beam according to the momentum per unit charge, The pass selection unit a slit extending in a direction perpendicular to the first direction and the upstream / downstream direction and opening to allow the beam to pass; a beam shielding portion formed at a position other than the slit and configured to block the beam by causing it to collide with the beam, 2. The particle beam therapy device according to claim 1, wherein the beams included in the mixed beam are passed through the slit at positions on an orbit corresponding to the momentum per unit charge of the cation beams included in the mixed beam, and the beams included in the mixed beam are shielded by the beam shielding unit at positions other than the positions on an orbit corresponding to the momentum per unit charge of the cation beams included in the mixed beam.

3. A particle beam therapy device as described in claim 1, wherein a quadrupole electromagnet is arranged between the deflection magnetic field and the passage selection section.

4. A particle beam therapy device as described in claim 3, wherein a quadrupole electromagnet is arranged downstream of the passage selection section.

5. 2. The particle beam therapy device according to claim 1, wherein the passing selection unit passes a beam having a momentum per unit charge that is the same as the momentum per unit charge of the positive ion beam in the mixed beam that has passed through the deflection magnetic field, and blocks a beam having a momentum per unit charge that is different from the momentum per unit charge of the positive ion beam in the mixed beam.

6. the deflection magnetic field causes the trajectories of the beams included in the mixed beam to differ depending on the momentum per unit charge upstream of the pass selection section; The pass selection unit 2. The particle beam therapy device according to claim 1, wherein the beams included in the mixed beam are passed at positions on an orbit corresponding to the momentum per unit charge of the positive ion beams included in the mixed beam, and the beams included in the mixed beam are shielded at positions other than the positions on an orbit corresponding to the momentum per unit charge of the positive ion beams included in the mixed beam.

7. 7. The particle beam therapy system according to claim 1, wherein the positive ion beam is a helium ion beam, and the other type of beam includes a deuterium ion beam.

8. 8. The particle beam therapy system according to claim 1, wherein the degrader is provided within a gantry, and the deflection magnetic field and the pass selection unit are provided within the gantry.

9. A particle beam therapy device for treating a patient by irradiating the patient with a positive ion beam, which is a helium ion beam or a carbon ion beam, a cyclotron that emits the positive ion beam; a degrader provided downstream of the cyclotron to reduce the energy of the positive ion beam; a deflection electromagnet provided downstream of the degrader, which deflects a mixed beam containing the positive ion beam and a beam of another type having a nuclide different from that of the positive ion beam generated by the positive ion beam passing through the degrader, and causes the trajectories of the beams contained in the mixed beam to vary according to the momentum per unit charge; a passage selection unit provided downstream of the bending electromagnet and configured to selectively pass the positive ion beam from the mixed beam.

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