Heavy particle beam irradiation device and treatment system

Abstract

To provide a highly efficient heavy particle beam irradiation device in which a degree of design freedom for an electric magnet is improved.SOLUTION: A heavy particle beam irradiation device 10 includes: an emission port 31 for emitting a heavy particle beam 18 in a direction of a predetermined emission angle φ from a fixed point of a reference line 16 that an isocenter 15 intersects with; electric magnets 45 (45a, 45b) forming magnetic field areas 11 (11a, 11b) in which magnetic fields 25 (25a, 25b) are in reverse directions sandwiching the reference line 16; and a current supply unit for supplying excitation current to the electric magnets 45 (45a, 45b) so that the strength of the magnetic fields 25 differs depending on the emission angle φ, and converging the heavy particle beam 18 to the isocenter 15.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a technique for irradiating a target with heavy particle beams from a plurality of directions.

Background Art

[0002] Particle beam therapy is performed to treat malignant tumors such as cancer by irradiating with heavy particle beams accelerated to high energy. According to this particle beam therapy, since it is possible to pinpoint the death of only the lesion tissue without damaging normal tissues, the burden on the patient is less than that of surgical and chemical therapies, and early social rehabilitation after treatment can also be expected.

[0003] In the initial irradiation treatment apparatus, the irradiation part of the heavy particle beam was fixed, and the fixed method that could irradiate the target in only one direction was the mainstream. In recent years, in order to perform more effective treatment, the heavy particle beam is irradiated so as to overlap the target (lesion tissue) from various directions to increase the concentration of the dose. By doing so, it is possible to apply a large dose to the target in the body while suppressing the exposure of normal tissues.

[0004] As such, as an apparatus for irradiating a target with heavy particle beams from various directions, techniques such as providing a plurality of fixed irradiation ports, rotating the target itself, or using a rotating gantry are widely known. Furthermore, there is a known technique of deflecting a heavy particle beam with an electromagnet and irradiating the target with the heavy particle beam from an arbitrary angle.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the known technique of deflecting the above-mentioned heavy particle beam with an electromagnet, the flight distance of the heavy particle beam becomes long from the time it is deflected at the exit port and given an exit angle until it enters the electromagnet. Further, since a magnetic field region for giving an irradiation angle to the target is formed over a wide range, the flight distance after entering the electromagnet is also long. Also, since the magnetic field strength in the magnetic field region is fixed regardless of the irradiation angle, the design freedom of the electromagnet is low.

[0007] Thus, since the flight distance of the heavy particle beam is very long without being converged and controlled, divergence increases, and there is a concern that it may contact the opposing surface of the electromagnet where a narrow magnetic field region is formed. When the heavy particle beam contacts the opposing surface of the electromagnet, beam loss occurs, resulting in a problem of reduced beam transport efficiency. Also, if the electromagnets are opposed with a gap to avoid contact of the heavy particle beam, the strength of the magnetic field region may decrease or the consumption of the excitation current may increase, leading to a decrease in efficiency.

[0008] The embodiments of the present invention have been made in consideration of such circumstances, and an object thereof is to provide a heavy particle beam irradiation device that improves the design freedom of the electromagnet and is excellent in efficiency.

Means for Solving the Problems

[0009] In a heavy particle beam irradiation device, an exit port that emits a heavy particle beam in a direction of a predetermined exit angle from a fixed point of a reference line where isocenters intersect, an electromagnet that forms a magnetic field region with opposite magnetic fields across the reference line, and a current supply unit that supplies an excitation current to the electromagnet so that the strength of the magnetic field varies according to the exit angle and converges the heavy particle beam to the isocenter.

Effects of the Invention

[0010] According to the embodiments of the present invention, a heavy particle beam irradiation device that improves the design freedom of the electromagnet and is excellent in efficiency is provided.

Brief Description of the Drawings

[0011]

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Figure 10

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Mode for Carrying Out the Invention

[0012] (First Embodiment) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a plan view of the heavy particle beam irradiation apparatus 10A (10) according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view of the electromagnet 45 (45a, 45b) that forms the magnetic field regions 11 (11a, 11b) in the first embodiment.

[0013] As described above, the heavy particle beam irradiation device 10 includes an extraction port 31 that extracts the heavy particle beam 18 in a direction at a predetermined extraction angle φ from a fixed point on the reference line 16 where the isocenter 15 intersects, electromagnets 45 (45a, 45b) that form magnetic field regions 11 (11a, 11b) in which the magnetic fields 25 (25a, 25b) are in opposite directions on either side of the reference line 16, and a current supply unit 52 (FIG. 3) that supplies excitation current to the electromagnets 45 (45a, 45b) so that the strength of the magnetic field 25 varies depending on the extraction angle φ, thereby converging the heavy particle beam 18 at the isocenter 15.

[0014] In Fig. 1, the isocenter 15 is the origin of the coordinate axes, the reference line 16 is the X-axis, the direction of the magnetic field 25 (25a, 25b) generated by the magnetic field region 11 (11a, 11b) is the Z-axis, and the direction perpendicular to the X-axis and Z-axis is the Y-axis. In treatment using the heavy particle beam 18, a mobile bed (not shown) is set so that the target (lesion tissue) of the patient lying down along the Z-axis direction coincides with the isocenter 15. Then, as necessary, the mobile bed is moved along each axis or in the rotational direction of the Y-axis to irradiate the heavy particle beam 18.

[0015] The extraction port 31 is mechanically adjusted so that the heavy particle beam 18 is incident on the isocenter 15 when the extraction angle φ is set to zero. The range of this extraction angle φ is set so that the heavy particle beam 18 output from the extraction port 31 can be incident on the magnetic field region 11. The heavy particle beam 18 traces an arc trajectory in the XY plane due to the Lorentz force applied in the magnetic field region 11, and converges on the isocenter 15.

[0016] As shown in FIG. 2, the magnetic field regions 11(11a, 11b) are composed of electromagnets 45(45a, 45b) that generate magnetic fields 25(25a, 25b) in a direction that applies a Lorentz force directed inward to the passing heavy particle beam 18. These electromagnets 45(45a, 45b) are composed of a pair of coils arranged in the Z direction and are arranged on both sides of the reference line 16 (X axis). Thereby, the heavy particle beam 18 incident on the magnetic field region 11 from the emission port 31 converges to the isocenter 15 along an arc trajectory. The irradiation angle θ of the heavy particle beam 18 converging to the isocenter 15 is defined in the XY plane with this isocenter 15 as the origin.

[0017] Each of the electromagnets 45(45a, 45b) has a coil wound around a high-permeability yoke (such as an iron core), and a high-intensity magnetic field 25(25a, 25b) can be generated in the gap between the opposing yokes. The higher the intensity of these magnetic fields 25(25a, 25b), the smaller the radius of the arc trajectory of the heavy particle beam 18 can be made, and the smaller the area of the magnetic field region 11(11a, 11b) can be made.

[0018] Therefore, if the electromagnets 45(45a, 45b) are made of superconducting coils, the magnetic field 25(25a, 25b) can be made even stronger, and the area of the magnetic field region 11(11a, 11b) can be made even smaller. Also, although each of the electromagnets 45(45a, 45b) is exemplified as being symmetric in plan view, it may be asymmetric as long as the symmetry of the emission angle φ is not questioned. Thereby, the unused regions can be omitted to form the magnetic field region 11, and the manufacturing cost and power consumption can be reduced.

[0019] FIG. 3 is a block diagram of a control unit 30A (30) that supplies an exciting current to electromagnets 45 (45a, 45b) in the first embodiment. This control unit 30 has a function of switching the supply amount of the exciting current to the electromagnets 45 (45a, 45b) according to the emission angle φ of the heavy particle beam 18 emitted from the emission port 31. For the magnetic field region 11 having an arbitrary shape, among the three relationships of the emission angle φ of the heavy particle beam 18, the exciting current of the electromagnet 45, and the irradiation angle θ, if one of the emission angle φ and the irradiation angle θ is determined, the remaining two are determined.

[0020] The control unit 30A includes a power supply 51 (51a, 51b) that generates power, and a current supply unit 52 that supplies an exciting current corresponding to either the set emission angle φ or the irradiation angle θ to the corresponding electromagnet 45 (45a, 45b). While the emission angle φ of the heavy particle beam 18 is small, the curvature of the arc trajectory in the magnetic field region 11 can be small. Therefore, the exciting current of the electromagnet 45 is sufficient with only one power supply 51a. On the other hand, when the emission angle φ of the heavy particle beam 18 becomes large, it is necessary to increase the curvature of the arc trajectory in the magnetic field region 11. In this case, the exciting current supplied to the electromagnet 45 is insufficient with only the capacity of one power supply 51, and the two power supplies 51a and 51b supply the exciting current simultaneously.

[0021] In this way, the exciting current can be variably supplied to the electromagnet 45 corresponding to either the set emission angle φ or the irradiation angle θ. Thereby, the intensity of the magnetic field 25 through which the heavy particle beam 18 passes can be made different according to the emission angle φ, and the curvature of the arc trajectory in the magnetic field region 11 can be arbitrarily set. This contributes to an improvement in the design freedom of the electromagnet forming the magnetic field region 11.

[0022] The nozzle 29 moves according to the emission angle φ and allows the heavy particle beam 18 to pass therethrough toward the isocenter 15. The inside of this nozzle 29 is maintained in a vacuum state, suppressing beam loss due to scattering until immediately before the isocenter 15. The nozzle 29 also has a function of adjusting so that the generation region of the dose peak of the heavy particle beam 18 coincides with the three-dimensional shape of the tumor (target). Note that, as adjustment methods of the heavy particle beam 18, there are an expanded beam method and a scanning method. The expanded beam method is a method of three-dimensionally expanding the heavy particle beam 18 with a scatterer or a ridge filter and shaping the beam with a compensation filter or a collimator dedicatedly created for each target. The scanning method is a method of scanning the trajectory of the heavy particle beam 18 according to the shape of the tumor.

[0023] Furthermore, the nozzle 29 may be provided with a range shifter for adjusting the maximum depth until the heavy particle beam 18 reaches the target. This range shifter adjusts the attenuation amount of the energy necessary and sufficient for the heavy particle beam 18 to reach the target by adjusting the thickness of the acrylic plate.

[0024] FIG. 4 is a partially enlarged view in a plan view of the heavy particle beam irradiation apparatus 10. As described above, the magnetic field region 11 is formed with its end boundary 12 such that the length of the linear trajectory of the heavy particle beam 18 (181 < 182 < 183) monotonically increases with an increase in the emission angle φ (φ1 < φ2 < φ3). Thereby, with an increase in the emission angle φ, the incident angle β (β1 > β2 > β3) of the heavy particle beam 18 to the end boundary 12 can be monotonically decreased.

[0025] The straight trajectory from when the heavy particle beam 18 is emitted from the emission port 31 until it enters the end boundary 12 is such that the magnetic field region 11 is formed so as to become shorter as the emission angle φ decreases. At this time, the incident angle β of the heavy particle beam 18 will increase as the emission angle φ decreases. Due to such differences in the incident angle β, a difference occurs in the magnetic field strength experienced, and the heavy particle beam 18 converges and diverges, changing the beam size. This will be described in detail in FIGS. 4, 5, and 6 by introducing a coordinate system with the incident direction of the heavy particle beam 18 as the a-axis, the direction of the magnetic field 25 as the c-axis, and the direction orthogonal to the a-axis and the c-axis as the b-axis.

[0026] FIG. 5 is an explanatory diagram of the divergence in the heavy particle beam 18 in the orbital plane (X-Y plane). As shown in this way, in the orbital plane (X-Y plane), the end part of the heavy particle beam 18 close to the reference line 16 has an earlier incident timing to the magnetic field region 11 compared to the far end part. As a result, the start of the arc trajectory also advances, and the beam width in the orbital plane expands from d to D (D1, D2, D3). Also, as the incident angle β (β1 > β2 > β3) of the heavy particle beam 18 decreases, the divergence degree of the beam width D (D1 < D2 < D3) in the orbital plane will expand.

[0027] FIG. 6 is an explanatory diagram of the convergence in the heavy particle beam 18 passing through the leakage magnetic field 25x of the electromagnet 45. FIG. 7(A) is an explanatory diagram of the Lorentz force F1 applied to the end part 191 of the heavy particle beam passing through the leakage magnetic field 25x on the S pole side. FIG. 7(B) is an explanatory diagram of the Lorentz force F2 applied to the end part 192 of the heavy particle beam passing through the leakage magnetic field 25x on the N pole side.

[0028] As shown in FIG. 6, at the end parts 191 and 192 of the heavy particle beam, the leakage magnetic field 25x has magnetic field components B a1 , B a2 along the incident direction (a-axis) of the heavy particle beam 18. And as shown in FIGS. 7(A) and 7(B), these magnetic field components B a1 , B a2 further have magnetic field components B a1 cosβ, B a2 cosβ in the b-axis direction. And these magnetic field components in the b-axis direction Ba1 cosβ, B a2 When the heavy particle beam 18 intersects with cosβ, Lorentz forces F1 and F2 in opposite directions are added along the c-axis direction. Here, q is the charge amount and v is the velocity.

[0029] F1 = qvB a1 cosβ ··· (1) F2 = qvB a2 cosβ ··· (2)

[0030] As shown in these formulas (1) and (2), the Lorentz forces F1 and F2 in opposite directions applied by the leakage magnetic field 25x compress the heavy particle beam 18 incident on the magnetic field region 11 in the direction of the magnetic field 25 (c-axis direction). Furthermore, as shown in formulas (1) and (2), as the incident angle β decreases, that is, as the length of the straight orbit of the heavy particle beam 18 (181, 182, 183) increases, the amount of compression of the beam diameter also increases. That is, as the length of the straight orbit of this heavy particle beam 18 (181 < 182 < 183) increases and the beam diameter becomes thicker due to self-divergence, the amount of compression by the leakage magnetic field 25x also increases, so the change in the beam width in the direction of the magnetic field 25 (c-axis direction) is offset.

[0031] In the electromagnet 45, a higher magnetic field can be generated more efficiently by setting a narrower gap between the magnetic poles. For this reason, there is little margin for the size of the heavy particle beam 18 in the direction of the magnetic field 25 (c-axis direction). However, according to this embodiment, the beam diameter can be compressed in the direction of the magnetic field 25 (c-axis direction) immediately before the heavy particle beam 18 enters the magnetic field region 11. Therefore, it is possible to avoid the heavy particle beam 18 contacting the magnetic pole surface of the electromagnet 45 and causing beam loss or reducing the beam transport efficiency.

[0032] (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. 8 to 10. FIG. 8 is a plan view of a heavy particle beam irradiation apparatus 10B(10) according to the second embodiment. FIG. 9 is a cross-sectional view of an electromagnet 45(45a1, 45a2, 45b1, 45b2) that forms a magnetic field region 11(11a1, 11a2, 11b1, 11b2) in the second embodiment.

[0033] In the heavy particle beam irradiation apparatus 10B of the second embodiment, with respect to the configuration of the first embodiment described above, each of the regions that form magnetic fields 25(25a1, 25a2)(25b1, 25b2) in the same direction among the magnetic field regions 11(11a1, 11a2)(11b1, 11b2) is divided and formed by a plurality of electromagnets 45(45a1, 45a2)(45b1, 45b2). In FIGS. 8 to 10, parts having the same configuration or function as those in FIGS. 1 to 3 are denoted by the same reference numerals, and redundant descriptions are omitted.

[0034] Thereby, when obtaining a desired irradiation angle θ, only one of the electromagnets 45(45a1, 45a2, 45b1, 45b2) arranged in the passage region of the heavy particle beam 18 is excited, and the electromagnets 45 in other regions are de-excited. When the heavy particle beam 18 passes through the regions of a plurality of electromagnets 45 (such as when passing directly above an adjacent boundary), only two adjacent electromagnets 45 need to be excited. By doing so, the region for generating the magnetic fields 25(25a1, 25a2, 25b1, 25b2) can be minimized. In addition, the inductance per electromagnet 45 can be reduced, the leakage magnetic field from the electromagnet 45 can also be reduced, and the influence on a patient (target) arranged at the isocenter 15 can be minimized.

[0035] And these electromagnets 45 (45a1, 45a2, 45b1, 45b2) are formed such that the inductance of the coils is equal. When dividing the area of the magnetic field regions 11 (11a1, 11a2, 11b1, 11b2), by making the area of each region equal, the inductance of the coils can be made equivalent. Thereby, the power supply connected to the electromagnet 45 can be simplified, the number of power supplies used can be reduced, and the number of electromagnets corresponding thereto can be increased, facilitating power supply management. Although an example of dividing the area of the magnetic field region 11 into four parts is shown, it may be divided further.

[0036] FIG. 10 is a block diagram of a control unit 30B that supplies an exciting current to the electromagnets 45 (45a1, 45a2, 45b1, 45b2) in the second embodiment. The control unit 30B includes a power supply 51 (51a, 51b) that generates power, and a current supply unit 52 that supplies an exciting current corresponding to either the set emission angle φ or the irradiation angle θ to the corresponding electromagnet 45 (45a1, 45a2, 45b1, 45b2). When the emission angle φ of the heavy particle beam 18 is small and the curvature of the arc trajectory in the magnetic field region 11 is small, the exciting current of the electromagnets 45 (45a1, 45b1) is sufficient with only one power supply 51a. On the other hand, when the emission angle φ of the heavy particle beam 18 becomes large, it is necessary to increase the curvature of the arc trajectory in the magnetic field region 11.

[0037] However, even in this case, since the corresponding magnetic field regions 11a2, 11b2 of the electromagnets 45 (45a2, 45b2) are small, the exciting current to be supplied is sufficient with only the capacity of one power supply 51a. The second power supply 51b is used as a backup. By selectively exciting the electromagnets 45 in this way, the generation of unnecessary magnetic fields can be suppressed, and energy consumption can be reduced. Also, the capacity of the power supply 51 to be installed can be reduced.

[0038] FIG. 11 is a schematic view of a treatment system 40 according to an embodiment of the present invention. As described above, the treatment system 40 includes an ion source 53 that generates heavy particles, an accelerator 20 that accelerates the heavy particles to generate a high-energy heavy particle beam 18, a beam transport path 49 that transports the heavy particle beam 18 extracted from the accelerator 20, an irradiation device 10 for the heavy particle beam 18, and a bed (not shown) that supports a target irradiated with the heavy particle beam 18 so as to be located at the isocenter 15.

[0039] The accelerator 20 is roughly classified into a linear accelerator 55 and a circular accelerator 56. The heavy particles generated by the ion source 53 are gradually accelerated by the linear accelerator 55 and the circular accelerator 56 to become the heavy particle beam 18. Then, the heavy particle beam 18 that has orbited the circular accelerator 56 and reached the irradiation required energy level has its traveling direction changed from the orbital path and is extracted into the beam transport path 49.

[0040] Examples of the heavy particles generated by the ion source 53 include carbon, helium, oxygen, neon, silicon, argon, etc. Examples of the ion source 53 include high-frequency (including microwaves) irradiation types such as an ECR (Electron Cyclotron Resonance) ion source and a PIG (Penning Ionization Gauge) ion source, as well as laser irradiation type ion sources. Note that the ion source 53 is not limited to these, and any ion source that can efficiently generate heavy particles can be appropriately adopted.

[0041] The linear accelerator 55 arranges a plurality of accelerating electric fields having opposite electric field components adjacent to each other in a straight line, repeatedly reverses the electric field direction at a high-frequency, and always accelerates the heavy particles passing through the accelerating electric field in only one direction. Specifically, the linear accelerator 55 is composed of a radio frequency quadrupole (RFQ) linear accelerator and a drift tube linac (DTL).

[0042] The circular accelerator 56 is a synchrotron, a cyclotron, or the like, and includes a high-frequency acceleration cavity 59 that accelerates the heavy particle beam 18 incident from the linear accelerator 55 by high-frequency power, a plurality of deflection electromagnets 58 that bend the heavy particle beam 18 by a magnetic field and place it on a circular orbit, a plurality of quadrupole electromagnets 57 that generate a magnetic field for diverging and converging the circulating heavy particle beam 18 and confining it within the circular orbit, and an emitter 54 that emits the heavy particle beam 18 from the circular accelerator 56 to the beam transport path 49.

[0043] The circular accelerator 56 configured in this way can accelerate the heavy particle beam 18 incident from the linear accelerator 55 at low energy to a high energy by finally accelerating it to 70 - 80% of the speed of light while circulating it.

[0044] According to the heavy particle beam irradiation device of at least one embodiment described above, when converging the heavy particle beam on the isocenter, by supplying an excitation current to the electromagnet so that the magnetic field strength varies according to the emission angle, it is possible to improve the design freedom of the electromagnet and provide a heavy particle beam irradiation device with excellent efficiency.

[0045] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0046] 10 (10A, 10B) … Heavy particle beam irradiation device, 11 (11a, 11b, 11a1, 11a2, 11b1, 11b2) … Magnetic field region, 12 (12a, 12b) … End boundary, 15 … Isocenter, 16 … Reference line, 18 … Heavy particle beam, 19 (191, 192) … Heavy particle beam end, 20 … Accelerator, 25 … Magnetic field, 25x … Leakage magnetic field, 29 … Nozzle, 30 (30A, 30B) … Control unit, 31 … Exit port, 40 … Treatment system, 45 (45a, 45b, 45a1, 45a2, 45b1, 45b2) … Electromagnet, 49 … Beam transport path, 51 (51a, 51b) … Power supply, 52 … Current supply unit, 53 … Ion source, 54 … Emitter, 55 … Linear accelerator, 56 … Circular accelerator, 57 … Quadrupole electromagnet, 58 … Deflection electromagnet, 59 … High-frequency acceleration cavity, φ … Exit angle, β … Incident angle, θ … Irradiation angle.

Claims

1. An emission port that emits a heavy particle beam in a direction of a predetermined emission angle from a fixed point of a reference line where isocenters intersect; An electromagnet that forms a magnetic field region with opposite magnetic fields across the reference line; A current supply unit that supplies an excitation current to the electromagnet so that the intensity of the magnetic field varies according to the emission angle, and converges the heavy particle beam to the isocenter. A heavy particle beam irradiation device comprising the same.

2. In the heavy particle beam irradiation device according to Claim 1, A heavy particle beam irradiation device in which an end boundary of the magnetic field region is formed such that the length of a straight orbit of the heavy particle beam monotonically increases with an increase in the emission angle.

3. In the heavy particle beam irradiation device according to Claim 1 or Claim 2, A heavy particle beam irradiation device comprising a nozzle that moves according to the emission angle and allows the heavy particle beam to pass therethrough toward the isocenter.

4. In the heavy particle beam irradiation device according to Claim 1 or Claim 2, In the heavy particle beam irradiation device, each of regions in the magnetic field region that form magnetic fields in the same direction is formed by being divided by a plurality of electromagnets.

5. In the heavy particle beam irradiation device according to Claim 4, In the heavy particle beam irradiation device, each of the electromagnets is formed such that the inductance of a coil is equal.

6. The heavy particle beam irradiation device according to Claim 1 or Claim 2, An ion source that generates heavy particles; An accelerator that accelerates the heavy particles to generate the heavy particle beam having high energy; A beam transport path that transports the heavy particle beam extracted from the accelerator; A treatment system comprising a bed that supports a target irradiated with the heavy particle beam so as to be located at the isocenter.

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