Heavy particle beam irradiation device and treatment system

Abstract

Provided is a heavy particle beam irradiation device that has an improved degree of freedom in designing electromagnets, and excellent efficiency.　A heavy particle beam irradiation device (10) comprises: an emission port (31) that emits heavy particle beams (18) in a direction of a prescribed emission angle φ from a fixed point on a reference line (16) at which an isocenter (15) intersects; electromagnets (45a, 45b) that form magnetic field regions (11a, 11b) in which magnetic fields (25a, 25b) are in opposite directions across the reference line (16); and an electric current supply unit that supplies excitation electric current to the electromagnets (45a, 45b) such that the strengths of the magnetic fields (25) are different according to the emission angle φ, and causes the heavy particle beams (18) to converge at the isocenter (15).

Description

Heavy particle beam irradiation equipment and treatment system

[0001] An embodiment of the present invention relates to a technique for irradiating a target with a heavy particle beam from multiple directions.

[0002] Particle therapy is used to treat malignant tumors such as cancer by irradiating them with a beam of heavy particles accelerated to high energy. This particle therapy can pinpoint and destroy only the diseased tissue without damaging normal tissue, so it places less of a burden on patients than surgical or chemical treatments and is expected to enable earlier rehabilitation after treatment.

[0003] Early irradiation therapy devices mainly used a fixed system in which the heavy particle beam irradiation unit was fixed and could only irradiate the target in one direction. In recent years, in order to provide more effective treatment, heavy particle beams have been irradiated from various directions so that the target (lesion tissue) overlaps, increasing the concentration of the dose. This makes it possible to deliver a large dose to the target inside the body while reducing exposure to normal tissue.

[0004] As such, there are well-known technologies for irradiating a target with a heavy particle beam from various directions, such as providing multiple fixed irradiation ports, rotating the target itself, or using a rotating gantry. Furthermore, there is a known technology for deflecting the heavy particle beam with an electromagnet to irradiate the target with the heavy particle beam from any angle.

[0005] Patent No. 6364141 Patent No. 6775860

[0006] In the known technique of deflecting a heavy particle beam with an electromagnet, the heavy particle beam has a long range from when it is deflected at the exit port and given an exit angle until it is incident on the electromagnet. Furthermore, since the magnetic field region that gives the heavy particle beam an irradiation angle to the target is formed over a wide area, the range after it is incident on the electromagnet is also long. Furthermore, since the magnetic field strength of the magnetic field region is fixed regardless of the irradiation angle, the degree of freedom in designing the electromagnet is low.

[0007] As described above, heavy particle beams have a very long range without focusing control, which increases divergence and raises concerns that they may come into contact with the opposing faces of electromagnets, which form narrow magnetic field regions. Contact of the heavy particle beam with the opposing faces of the electromagnets results in beam loss and reduced beam transport efficiency, which is problematic. Furthermore, if the opposing electromagnets are spaced apart to avoid contact, the strength of the magnetic field region will decrease or the consumption of excitation current will increase, resulting in reduced efficiency.

[0008] The embodiments of the present invention have been made in consideration of the above circumstances, and have an object to provide a heavy particle beam irradiation device that improves the degree of freedom in designing electromagnets and is highly efficient.

[0009] FIG. 1 is a plan view of a heavy particle beam irradiation device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of an electromagnet that forms a magnetic field region in the first embodiment. FIG. 3 is a block diagram of a control unit that supplies an excitation current to the electromagnet in the first embodiment. FIG. 4 is a partially enlarged plan view of a heavy particle beam irradiation device. FIG. 5 is an explanatory diagram of divergence of a heavy particle beam in an orbital plane (X-Y plane). FIG. 6 is an explanatory diagram of convergence of a heavy particle beam that passes through a leakage magnetic field of an electromagnet. (A) An explanatory diagram of the Lorentz force imparted to an end of a heavy particle beam that passes through a leakage magnetic field on the south pole side, (B) An explanatory diagram of the Lorentz force imparted to an end of a heavy particle beam that passes through a leakage magnetic field on the north pole side. FIG. 1 is a plan view of a heavy particle beam irradiation device according to a second embodiment. FIG. 2 is a cross-sectional view of an electromagnet that forms a magnetic field region in the second embodiment. FIG. 3 is a block diagram of a control unit that supplies an excitation current to the electromagnet in the second embodiment. FIG. 4 is a configuration diagram of a treatment system according to an embodiment of the present invention.

[0010] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a plan view of a heavy particle beam irradiation device 10A (10) according to a first embodiment of the present invention. Fig. 2 is a cross-sectional view of electromagnets 45 (45a, 45b) that form magnetic field regions 11 (11a, 11b) in the first embodiment.

[0011] As described above, the heavy particle beam irradiation device 10 includes an extraction port 31 that extracts the heavy particle beam 18 in the direction of 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 directed in opposite directions across the reference line 16, and a current supply unit 52 (FIG. 3) that supplies excitation currents to the electromagnets 45 (45a, 45b) so that the strength of the magnetic field 25 varies depending on the extraction angle φ, thereby focusing the heavy particle beam 18 on the isocenter 15.

[0012] 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 rotated around the Y-axis to irradiate the heavy particle beam 18.

[0013] The extraction port 31 is mechanically adjusted so that when the extraction angle φ is set to zero, the heavy particle beam 18 is incident on the isocenter 15. 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.

[0014] As shown in Figure 2, the magnetic field region 11 (11a, 11b) is composed of electromagnets 45 (45a, 45b) that generate a magnetic field 25 (25a, 25b) in a direction that applies an inward Lorentz force to the passing heavy particle beam 18. These electromagnets 45 (45a, 45b) are made up of a pair of coils arranged in the Z direction and are arranged on both sides of the reference line 16 (X axis). As a result, the heavy particle beam 18 that has entered the magnetic field region 11 from the exit port 31 traces an arc trajectory and converges on the isocenter 15. The irradiation angle θ of the heavy particle beam 18 that converges on the isocenter 15 is defined in an XY plane with the isocenter 15 as the origin.

[0015] Each of the electromagnets 45 (45 a, 45 b) has a coil wound around a yoke (iron core, etc.) with high magnetic permeability, and can generate a high-intensity magnetic field 25 (25 a, 25 b) in the gap between the opposing yokes. The higher the intensity of these magnetic fields 25 (25 a, 25 b), the smaller the radius of the arc trajectory of the heavy particle beam 18 can be, and the smaller the area of ​​the magnetic field region 11 (11 a, 11 b) can be.

[0016] 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 further reduced. Also, while the electromagnets 45 (45a, 45b) are symmetrical in plan view, they may be asymmetrical as long as the symmetry of the emission angle φ is not an issue. This allows the magnetic field region 11 to be formed by omitting unused regions, thereby reducing manufacturing costs and power consumption.

[0017] 3 is a block diagram of the control unit 30A (30) that supplies excitation current to the electromagnets 45 (45a, 45b) in the first embodiment. The control unit 30 has a function of switching the amount of excitation current supplied to the electromagnets 45 (45a, 45b) depending on the extraction angle φ of the heavy particle beam 18 extracted from the extraction port 31. Note that for the magnetic field region 11 having an arbitrary shape, the relationship between the extraction angle φ of the heavy particle beam 18, the excitation current of the electromagnets 45, and the irradiation angle θ is such that if one of the extraction angle φ and the irradiation angle θ is determined, the other two are determined.

[0018] The control unit 30A is composed of a power supply 51 (51a, 51b) that generates electric power, and a current supply unit 52 that supplies an excitation current corresponding to either the set extraction angle φ or the irradiation angle θ to the corresponding electromagnet 45 (45a, 45b). While the extraction 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 excitation current of the electromagnet 45 is sufficient with only one power supply 51a. On the other hand, when the extraction angle φ of the heavy particle beam 18 increases, the curvature of the arc trajectory in the magnetic field region 11 must also increase. In this case, the capacity of only one power supply 51 is insufficient for the excitation current to be supplied to the electromagnet 45, and therefore the two power supplies 51a, 51b simultaneously supply the excitation current.

[0019] In this way, the excitation current can be variably supplied to the electromagnet 45 in accordance with either the set extraction angle φ or the irradiation angle θ. This makes it possible to vary the strength of the magnetic field 25 through which the heavy particle beam 18 passes depending on the extraction angle φ, and to arbitrarily set the curvature of the arc trajectory in the magnetic field region 11. This contributes to improving the degree of freedom in designing the electromagnets that form the magnetic field region 11.

[0020] The nozzle 29 moves according to the emission angle φ and passes the heavy particle beam 18 toward the isocenter 15. The nozzle 29 is maintained in a vacuum state inside, suppressing beam loss due to scattering until just before the isocenter 15. The nozzle 29 also has the function of adjusting the region where the dose peak of the heavy particle beam 18 occurs so that it matches the three-dimensional shape of the tumor (target). The heavy particle beam 18 can be adjusted using an expanded beam method or a scanning method. The expanded beam method is a method in which the heavy particle beam 18 is expanded three-dimensionally using a scatterer or a ridge filter, and the beam shape is adjusted using a compensation filter or collimator specially designed for each target. The scanning method is a method in which the trajectory of the heavy particle beam 18 is scanned to match the shape of the tumor.

[0021] Furthermore, the nozzle 29 may be provided with a range shifter for adjusting the maximum depth to which the heavy particle beam 18 reaches the target. This range shifter adjusts the attenuation of the energy necessary and sufficient for the heavy particle beam 18 to reach the target by adjusting the thickness of the acrylic plate.

[0022] 4 is a partially enlarged plan view of the heavy particle beam irradiation device 10. As described above, the end boundaries 12 of the magnetic field region 11 are formed so that the length of the linear trajectory of the heavy particle beam 18 (18<18<18) monotonically increases with an increase in the extraction angle φ (φ<φ<φ). This allows the incident angle β (β>β>β) of the heavy particle beam 18 to the end boundary 12 to monotonically decrease with an increase in the extraction angle φ.

[0023] The magnetic field region 11 is formed so that the linear trajectory of the heavy particle beam 18 from the exit port 31 to its incidence on the end boundary 12 becomes shorter as the exit angle φ becomes smaller. At this time, the incidence angle β of the heavy particle beam 18 increases as the exit angle φ becomes smaller. Such a difference in the incidence angle β causes a difference in the magnetic field strength experienced, causing the heavy particle beam 18 to converge or diverge, resulting in a change in beam size. This will be described in detail with reference to Figures 4, 5, and 6, introducing a coordinate system in which the incidence direction of the heavy particle beam 18 is the a-axis, the direction of the magnetic field 25 is the c-axis, and the direction perpendicular to the a-axis and c-axis is the b-axis.

[0024] 5 is an explanatory diagram of the divergence of the heavy particle beam 18 in the orbital plane (X-Y plane). As described above, in the orbital plane (X-Y plane), the end of the heavy particle beam 18 closer to the reference line 16 has an earlier injection timing into the magnetic field region 11 than the far end, and as a result, the start of the arcuate orbit also occurs earlier, and the beam width in the orbital plane expands from d to D (D1, D2, D3). Furthermore, as the incidence angle β (β1>β2>β3) of the heavy particle beam 18 decreases, the divergence of the beam width D (D1<D2<D3) in the orbital plane expands.

[0025] Fig. 6 is an explanatory diagram of the convergence of 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 heavy particle beam end 191 passing through the leakage magnetic field 25x on the south pole side. Fig. 7(B) is an explanatory diagram of the Lorentz force F2 applied to the heavy particle beam end 192 passing through the leakage magnetic field 25x on the north pole side.

[0026] As shown in FIG. 6, at the heavy particle beam ends 19 and 19, the leakage magnetic field 25x is a magnetic field component B a1 , B a2 As shown in Figures 7(A) and 7(B), these magnetic field components B a1 , B a2 is further divided into magnetic field components B a1 cosβ, B a2 cosβ. And these b-axis magnetic field components B a1 cosβ, B a2 When the heavy particle beam 18 intersects with cos β, Lorentz forces F1 and F2 in opposite directions are applied along the c-axis direction, where q is the charge amount and v is the velocity.

[0027] F1 = qvB a1 cosβ...(1) F2=qvB a2 cosβ (2)

[0028] As shown in these formulas (1) and (2), the Lorentz forces F and F, which are directed in opposite directions and are applied by the leakage magnetic field 25x, compress the heavy particle beam 18 entering 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 incidence angle β decreases, i.e., as the length of the linear trajectory of the heavy particle beam 18 (18, 18, 18) increases, the amount of compression of the beam diameter also increases. That is, as the length of the linear trajectory of this heavy particle beam 18 (18 < 18 < 18) increases, the beam diameter becomes wider due to self-divergence, and 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.

[0029] The electromagnet 45 can generate a magnetic field more efficiently when the distance between the magnetic poles is set narrower. Therefore, 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. This makes it possible to avoid the heavy particle beam 18 coming into contact with the magnetic pole faces of the electromagnet 45, resulting in beam loss and a decrease in beam transport efficiency.

[0030] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 8 to Fig. 10. Fig. 8 is a plan view of a heavy particle beam irradiation device 10B (10) according to the second embodiment. Fig. 9 is a cross-sectional view of electromagnets 45 (45a1, 45a2, 45b1, 45b2) that form magnetic field regions 11 (11a1, 11a2, 11b1, 11b2) in the second embodiment.

[0031] In the heavy particle beam irradiation device 10B of the second embodiment, compared to the configuration of the first embodiment described above, each of the regions forming 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 Figures 8 to 10, parts having the same configuration or function as those in Figures 1 to 3 are indicated by the same reference numerals, and duplicated explanations will be omitted.

[0032] As a result, when a desired irradiation angle θ is obtained, only one of the electromagnets 45 (45a1, 45a2, 45b1, 45b2) arranged in the passage area of ​​the heavy particle beam 18 is excited, and the electromagnets 45 in other areas are de-energized. When the heavy particle beam 18 passes through areas of multiple electromagnets 45 (such as when it passes directly above the boundary between adjacent electromagnets), it is sufficient to energize only the two adjacent electromagnets 45. In this way, the area in which the magnetic field 25 (25a1, 25a2, 25b1, 25b2) is generated can be minimized. Furthermore, the inductance per electromagnet 45 can be reduced, and the leakage magnetic field from the electromagnets 45 can also be reduced, minimizing the impact on the patient (target) arranged at the isocenter 15.

[0033] These electromagnets 45 (45a1, 45a2, 45b1, 45b2) are formed so that their coil inductances are equal. When dividing the magnetic field region 11 (11a1, 11a2, 11b1, 11b2), the areas of the respective regions are made equal, thereby making it possible to equalize the coil inductances. This simplifies the power supplies connected to the electromagnets 45, reducing the number of power supplies used and increasing the number of electromagnets corresponding to each region, making power supply management easier. Note that while an example in which the magnetic field region 11 is divided into four regions is shown, it may be divided into more than four regions.

[0034] 10 is a block diagram of a control unit 30B that supplies excitation currents to the electromagnets 45 (45a1, 45a2, 45b1, 45b2) in the second embodiment. The control unit 30B is composed of power supplies 51 (51a, 51b) that generate electric power and a current supply unit 52 that supplies excitation currents corresponding to either the set extraction angle φ or the set irradiation angle θ to the corresponding electromagnets 45 (45a1, 45a2, 45b1, 45b2). When the extraction angle φ of the heavy particle beam 18 is small and the curvature of the arcuate trajectory in the magnetic field region 11 is small, only one power supply 51a is sufficient for the excitation current of the electromagnets 45 (45a1, 45b1). On the other hand, when the extraction angle φ of the heavy particle beam 18 increases, the curvature of the arcuate trajectory in the magnetic field region 11 must also increase.

[0035] However, even in this case, since the magnetic field regions 11a and 11b corresponding to the electromagnets 45 (45a and 45b) are small, the capacity of only one power supply 51a is sufficient to supply the excitation current. 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, reducing energy consumption. Furthermore, the capacity of the power supply 51 to be installed can be reduced.

[0036] 11 is a schematic diagram 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 for generating heavy particles, an accelerator 20 for accelerating the heavy particles to generate a high-energy heavy particle beam 18, a beam transport path 49 for transporting 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) for supporting a target to be irradiated with the heavy particle beam 18 so as to be positioned at an isocenter 15.

[0037] The accelerators 20 are roughly classified into a linear accelerator 55 and a circular accelerator 56, and the heavy particles generated in the ion source 53 are accelerated in stages by the linear accelerator 55 and the circular accelerator 56 to become a heavy particle beam 18. Then, the heavy particle beam 18 orbits around the circular accelerator 56 and reaches an energy level required for irradiation, and its traveling direction is changed from the orbit and it is extracted to the beam transport path 49.

[0038] 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 microwave) irradiation types such as an ECR (Electron Cyclotron Resonance) ion source and a PIG (Penning Ionization Gauge) ion source, as well as laser irradiation types. Note that the ion source 53 is not limited to these, and any suitable source may be used as long as it can efficiently generate heavy particles.

[0039] The linear accelerator 55 has a plurality of accelerating electric fields, each having an electric field component in an opposite direction to the adjacent electric field components, arranged in a line, and repeatedly reverses the electric field direction at a high frequency, thereby accelerating heavy particles passing through the accelerating electric fields in only one direction at all times. Specifically, the linear accelerator 55 is composed of a radio frequency quadrupole (RFQ) linear accelerator and a drift tube linac (DTL).

[0040] The circular accelerator 56 is a synchrotron, a cyclotron, or the like, and is composed of a radio-frequency acceleration cavity 59 that accelerates the heavy particle beam 18 incident from the linear accelerator 55 using radio-frequency power, a plurality of bending electromagnets 58 that bend the heavy particle beam 18 using a magnetic field and place it on an orbit, a plurality of quadrupole electromagnets 57 that generate a magnetic field that diverges and converges the orbiting heavy particle beam 18 and keeps it within the orbit, and an extractor 54 that extracts the heavy particle beam 18 from the circular accelerator 56 to the beam transport path 49.

[0041] The circular accelerator 56 configured in this manner can accelerate the heavy particle beam 18 incident at low energy from the linear accelerator 55 to 70 to 80% of the speed of light while circulating it, ultimately increasing the energy.

[0042] According to at least one of the embodiments of the heavy ion beam irradiation device described above, when converging the heavy ion beam at the isocenter, an excitation current is supplied to the electromagnet so that the magnetic field strength varies depending on the exit angle, thereby improving the design freedom of the electromagnet and making it possible to provide a heavy ion beam irradiation device with excellent efficiency.

[0043] 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, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as the inventions described in the claims and their equivalents.

Claims

1. A heavy particle beam irradiation device comprising: 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 field directions across the reference line; and 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 on the isocenter.

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

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

4. The heavy particle beam irradiation device according to claim 1 or 2, wherein each of the regions forming the magnetic field in the same direction in the magnetic field region is formed by dividing with a plurality of electromagnets.

5. The heavy particle beam irradiation device according to claim 4, wherein each of the electromagnets is formed such that the inductance of the coil is equal.

6. A treatment system comprising: the heavy particle beam irradiation device according to claim 1 or 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 taken out from the accelerator; and a bed that supports a target irradiated with the heavy particle beam so as to be located at the isocenter.

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