Accelerator and particle beam therapy system

Abstract

The present application aims at making the operation of extracting an ion beam from an accelerator fast. The accelerator (100) has an upper magnetic pole (8) and a lower magnetic pole (9) that sandwich an ion circulating space (10) in which ions perform a circulating motion. At least one of the upper magnetic pole (8) and the lower magnetic pole (9) is formed so that, when the ion circulating space (10) is observed along the ion beam orbit, the magnetic pole interval between the upper magnetic pole (8) and the lower magnetic pole (9) varies. That is, a wide interval region (11) in which the magnetic pole interval is larger than the peripheral region is formed in a region on the center point side of the ion circulating space (10) than the center point of the ion beam orbit.

Description

TECHNICAL FIELD

[0001] The present application relates to an accelerator and a particle beam therapy system, and particularly relates to a technique for extracting an ion beam from an accelerator. BACKGROUND

[0002] Particle beam therapy in which a particle beam is irradiated to a lesion is being widely used. Generally, a particle beam therapy system equipped with an accelerator is used in the particle beam therapy. Ions such as carbon ions, helium ions, and protons are injected into the accelerator, and the ions are accelerated to have a desired energy for therapy. A beam formed of the ions accelerated by the accelerator is irradiated toward a lesion. In the particle beam therapy system, the energy and the spatial spread of the ion beam are adjusted in accordance with the position and shape of the lesion.

[0003] As a document related to the particle beam therapy system, Patent Literature 1 below is known. In Patent Literature 1, as a method for "controlling the emission of a charged particle beam from a circular accelerator with high precision, and improving the radiation dose rate in a circular accelerator in which the charged particle beam is accelerated while increasing the orbit radius by applying high frequency in a main magnetic field", a method of "emitting the charged particle beam by applying high frequency different from the high frequency for acceleration to the charged particle beam" is disclosed. In addition, an embodiment of "emitting from the accelerator while arbitrarily changing the beam energy between 70 MeV and 235 MeV" is disclosed.

[0004] Prior Art Documents

[0005] Patent Literature

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2019-133745

[0007] Patent Literature 2: Japanese Patent Application Laid-Open No. 2019-96404 SUMMARY

[0008] Problems to be Solved by the Invention

[0009] The accelerator disclosed in Patent Literature 1 has a configuration in which the orbit (beam orbit) of the ion beam is decentered. By the decentered configuration, a convergence region in which the intervals of the beam orbits different in energy from each other are narrowed is generated in the accelerator. In the convergence region, an electrode of a high frequency injector is disposed in a manner of sandwiching the beam orbit included in the energy range to be extracted. By applying a high frequency voltage to the high frequency injector, the amplitude of the betatron oscillation of the ion beam through the region sandwiched by the electrodes of the high frequency injector becomes large. And the ion beam after the amplitude of the betatron oscillation becomes large reaches a stripper magnetic field region and a regenerator magnetic field region disposed in a region radially outward of the maximum energy orbit, and is acted on by them, so that the ion beam is extracted outside the accelerator.

[0010] In such an accelerator, in the ion beam taken out in a certain energy range, the smaller the energy of the ion beam, the smaller the radius of the beam orbit, and the farther the distance from the stripper magnetic field region and the regenerator magnetic field region. Therefore, the amplitude of the vibration of the electron induction accelerator required for the taking out of the ion beam is large. Therefore, when the ion beam is taken out to the outside of the accelerator, sometimes the smaller the energy of the ion beam, the longer the response time from when the high-frequency voltage is applied to the high-frequency injector to when the ion beam is taken out.

[0011] The object of the present application is to make the operation of taking out the ion beam from the accelerator fast.

[0012] Means for solving the problem

[0013] The present application is characterized by having an upper magnetic pole and a lower magnetic pole that sandwich an ion circulating space in which an ion performs a circulating motion, and is configured so that a magnetic field variation in space when the ion circulating space is observed along an ion beam orbit is applied, and the magnetic field variation is a variation in the magnetic field in space that displaces the ion in such a manner that the smaller the energy of the ion, the larger the displacement amount of the ion in the outward direction at the ion taking-out operation point.

[0014] In addition, the present application is characterized by having an upper magnetic pole and a lower magnetic pole that sandwich an ion circulating space in which an ion performs a circulating motion, and is configured so that a magnetic field variation in space when the ion circulating space is observed along an ion beam orbit is applied, and the magnetic field variation is a variation in the magnetic field in space that displaces the ion in such a manner that the smaller the energy of the ion, the larger the displacement amount of the ion in the outward direction at the ion taking-out operation point.

[0015] In addition, the present application is characterized by having an upper magnetic pole and a lower magnetic pole that sandwich an ion circulating space in which an ion performs a circulating motion, and is configured so that a magnetic field variation in space when the ion circulating space is observed along an ion beam orbit is applied, and the magnetic field variation is a variation in the magnetic field in space that displaces the ion in such a manner that the smaller the energy of the ion, the larger the displacement amount of the ion in the outward direction at the ion taking-out operation point.

[0016] Effects of the Invention

[0017] According to the present application, the operation of taking out the ion beam from the accelerator becomes fast. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a perspective view of an accelerator.

[0019] Figure 2 is a view showing a cross section that appears when the accelerator is cut with a vertical plane.

[0020] Figure 3 is a plan view of the accelerator cut with a reference plane and viewed from above.

[0021] Figure 4 is a graph showing the distribution of the average value of the circumferential magnetic field.

[0022] Figure 5 is a graph showing the distribution of the circumferential magnetic field along the beam orbit and the magnetic pole interval.

[0023] Figure 6 is a graph showing the amount of displacement of the beam orbit to the radial direction when a constant magnetic field is applied throughout one turn of the beam orbit.

[0024] Figure 7 is a plan view of the accelerator cut by a reference plane and viewed from above.

[0025] Figure 8 is a graph showing the distribution of the magnetic field along the beam orbit.

[0026] Figure 9 is a graph showing the structure of a particle ray therapy system. DETAILED DESCRIPTION

[0027] Hereinafter, an embodiment of the present application will be described with reference to the drawings. The same reference signs are assigned to the same matters shown in the plurality of drawings, and repeated description is avoided. In addition, the terms indicating shapes in the present specification, such as "circle", "cylinder", and the like, do not mean only a shape defined strictly in geometry. The terms indicating shapes in the present specification also mean a shape to which a deformation is applied within a range in which the function of a constituent element can be ensured. In addition, the terms "horizontal", "upper", "lower", and the like in the present specification are for convenience of explanation, and do not limit the posture at the time of installation of the accelerator.

[0028] <First Embodiment>

[0029] Figure 1 A perspective view of the accelerator 100 of the first embodiment of the present application is shown. The ions accelerated by the accelerator 100 can be hydrogen ions, i.e., protons. In the case where protons are accelerated, the energy of the ion beam taken out from the accelerator 100 is, for example, 70 MeV or more and 225 MeV or less.

[0030] The accelerator 100 is provided with a main magnetic field magnet 1. The main magnetic field magnet 1 has an upper return yoke 4 and a lower return yoke 5 which are circular in view from the vertical direction. The upper return yoke 4 is formed into a cylindrical container shape by a circular plate-shaped top plate and a side wall provided around the top plate. The lower return yoke 5 is formed into a cylindrical container shape by a circular plate-shaped bottom plate and a side wall provided around the bottom plate.

[0031] The upper return yoke 4 and the lower return yoke 5 are engaged in a manner that respective openings are aligned. The ion beam in acceleration circulates on a reference plane 2 that is a plane on which the upper return yoke 4 and the lower return yoke 5 are engaged. The upper return yoke 4 and the lower return yoke 5 can be a shape that is face symmetric about a vertical plane 3 that is perpendicular to the reference plane 2 and that passes through a magnetic pole center axis 13 that is a center axis of the magnetic poles of the main magnetic field magnet 1. Figure 1 In FIG. 1, a line at which the reference plane 2 intersects the main magnetic field magnet 1 and a line at which the vertical plane 3 intersects the main magnetic field magnet 1 are indicated by a single-dot chain line.

[0032] An ion source 1003 is provided on an upper side of the main magnetic field magnet 1, and a through-hole 24 through which ions are incident is provided in the upper return yoke 4. The ion source 1003 can also be provided inside the main magnetic field magnet 1.

[0033] A cross section that appears when the accelerator 100 is cut by the vertical plane 3 is shown in FIG. 2. As shown in FIG. 2, a pair of coils 6 are arranged face symmetrically about the reference plane 2 in a space surrounded by the upper return yoke 4 and the lower return yoke 5. Figure 2 Figure 2 A cross section that appears when the accelerator 100 is cut by the vertical plane 3 is shown in FIG. 2. As shown in FIG. 2, a pair of coils 6 are arranged face symmetrically about the reference plane 2 in a space surrounded by the upper return yoke 4 and the lower return yoke 5.

[0034] The coils 6 are superconducting coils that are provided inside a cryostat (not shown). The coils 6 are cooled in the cryostat by a refrigerant such as liquid helium or a refrigerator (not shown).

[0035] A vacuum vessel 7 is provided inside the coils 6 in the space surrounded by the upper return yoke 4 and the lower return yoke 5. Inside the vacuum vessel 7, an upper magnetic pole 8 and a lower magnetic pole 9 are arranged in a manner that they face each other. That is, the upper magnetic pole 8 is arranged on a lower surface of the upper return yoke 4, and the lower magnetic pole 9 is arranged on an upper surface of the lower return yoke 5. An ion circulating space 10 in which an ion beam is made to circulate and accelerate is formed between the upper magnetic pole 8 and the lower magnetic pole 9.

[0036] The upper return yoke 4, the lower return yoke 5, the upper magnetic pole 8, and the lower magnetic pole 9 are, for example, made of pure iron, low-carbon steel, or the like in which impurity concentration is reduced. The vacuum vessel 7 is, for example, made of stainless steel or the like. The coils 6 are, for example, made of superconducting wire in which a superconductor such as niobium titanium is used.

[0037] The ejection passage 1019 is provided with an electromagnet that is connected to an ejection passage power source via the through-hole 15. Current is supplied from the ejection passage power source to the electromagnet provided in the ejection passage 1019, and thus the ion beam that has reached the ejection passage 1019 is adjusted, and the ion beam is transported to a beam transport system that is connected to the accelerator 100.

[0038] ​In the present embodiment, the magnetic pole center axis 13 and the ion incidence axis 12 are different in position. Also, the high-frequency ejector 40 is located near the outer periphery of the ion circulating space 10. The ion incidence axis 12 along the through-hole 24 for ion incidence is located between the magnetic pole center axis 13 and the high-frequency ejector 40. The high-frequency ejector 40 is combined to the upper magnetic pole 8 and the lower magnetic pole 9 by a support member composed of a non-magnetic insulator, and is supported by the support member.

[0039] In Figure 3 a plan view of the accelerator 100 cut by the reference plane 2 and viewed from above the return yoke 5 side is shown. The main magnetic field magnet 1 of the present embodiment has a configuration symmetric with respect to the reference plane 2 in the up-down direction, and therefore, the configuration of the upper side of the main magnetic field magnet 1 is simplified in the following description. Figure 2 and Figure 3 are used to describe the configuration of the lower side of the main magnetic field magnet 1, and the description of the configuration of the upper side of the main magnetic field magnet 1 is simplified.

[0040] Figure 3 In

[0041] The center point O3 of the beam orbit 126 (hereinafter, the beam orbit is referred to as the beam orbit) corresponding to the ion beam having the maximum energy among the extracted ion beams coincides substantially with the magnetic pole center axis 13. The center point O3 of the beam orbit 126 corresponding to the ion beam having the minimum energy among the extracted ion beams is located on a line segment connecting the magnetic pole center point O2 and the ion incidence point Ol. Here, the ion incidence point Ol is the intersection of the ion incidence axis 12 and the reference plane 2. Also, the magnetic pole center point O2 is the intersection of the magnetic pole center axis 13 and the reference plane 2, and is the center point of the ion circulating space 10.

[0042] From the ion incidence point Ol, the region on the side opposite to the magnetic pole center point O2 is a convergence region in which the beam orbits are shifted and the orbit intervals are narrowed. On the other hand, from the ion incidence point Ol, the magnetic pole center point O2 side is a dispersion region in which the beam orbits are shifted and the orbit intervals are widened. The high-frequency ejector 40 is disposed at the ion extraction action point O4 in the convergence region, and the beam orbit 126 corresponding to the low energy and the beam orbit 127 corresponding to the high energy pass through the high-frequency ejector 40.

[0043] Here, the ion extraction operation point O4 is a point at which a physical phenomenon occurs that increases the amplitude of the vibration of the electron induction accelerator. The ion extraction operation point O4 in the present embodiment is a point that, viewed from the ion incidence point O1, is located on the side opposite the pole center point O2 and on the beam orbit of the ions that have reached the extracted energy. The ion extraction operation point O4 is considered on each beam orbit of the ion beams that differ in energy. The ion extraction operation point O4 is located on a straight line that links the pole center point O2 and the ion incidence point O1. At the ion extraction operation point O4, a high-frequency electric field for increasing the amplitude of the vibration of the electron induction accelerator is applied to the ion beam. As a modification, the ion extraction operation point O4 can not necessarily be located on the straight line that links the pole center point O2 and the ion incidence point O1.

[0044] In the vicinity of the high-frequency injector 40 disposed at the ion extraction operation point O4, trimming coils 51 and 52 are disposed with the vertical plane 3 interposed therebetween. Although not shown in FIG. 10, one pair of trimming coils 51 is disposed with the reference plane 2 interposed therebetween, and one pair of trimming coils 52 is disposed with the reference plane 2 interposed therebetween. The trimming coils 51 and 52 can be disposed only on the upper side or the lower side, respectively, in addition to being disposed with one pair of coils disposed with the reference plane 2 interposed therebetween. In addition, on the side opposite the ion incidence point O1 and the ion extraction operation point O4 (the position of the high-frequency injector 40), a pair of trimming coils 53 is disposed with the reference plane 2 interposed therebetween. Figure 3

[0045] The high-frequency acceleration cavity 1037 has a shape of a sector that covers a part of the interval of the beam orbit on the side opposite the ion extraction operation point O4, viewed from the ion incidence point O1. The high-frequency acceleration cavity 1037 is connected to the waveguide outside the accelerator 100 through through-holes 16 provided in the side walls of the upper return yoke 4 and the lower return yoke 5. As shown in FIG. 11, one of the pair of trimming coils 53 is disposed in the space between the high-frequency acceleration cavity 1037 and the upper pole 8, and the other of the pair of trimming coils 53 is disposed in the space between the high-frequency acceleration cavity 1037 and the lower pole 9. Figure 2

[0046] The upper trimming coil 53 can be mounted to the upper pole 8. Similarly, the lower trimming coil 53 can be mounted to the lower pole 9. The trimming coil 53 can be disposed only above the high-frequency acceleration cavity 1037 and not below the high-frequency acceleration cavity 1037. In addition, the trimming coil 53 can be disposed only below the high-frequency acceleration cavity 1037 and not above the high-frequency acceleration cavity 1037.

[0047] ​​Thus, the trimming coil 53 is provided at least one of the upper pole 8 side and the lower pole 9 side from the reference plane 2 sandwiched by the upper pole 8 and the lower pole 9. As described later, the trimming coil 53 generates a spatial variation of the magnetic field when the ion circulating space 10 is observed along the beam orbit.

[0048] In the wide interval region 11 shown by a single-dot chain line in FIG. 1, a pole interval as a distance between the upper pole 8 and the lower pole 9 is larger than a region of the periphery of the non-wide interval region 11. The wide interval region 11 can be, for example, a region extending to a predetermined azimuthal range toward a side opposite to a side where the high-frequency ejector 40 is disposed, as viewed from the center of each beam orbit corresponding to different energies. The wide interval region 11 can be provided, for example, over a region occupied by the beam orbit corresponding to the energy of the extracted object. That is, the wide interval region 11 can also be provided near the outer periphery of the ion circulating space 10. In the wide interval region 11, the upper pole 8 can be recessed upward, and the lower pole 9 can be recessed downward. Alternatively, in the wide interval region 11, both the upper pole 8 and the lower pole 9 can be recessed upward and downward. Figure 3 The gradient magnetic field magnet 31 (stripper) and the gradient magnetic field magnet 32 (regenerator) are disposed on the outer periphery side of the high-frequency ejector 40 with the vertical plane 3 sandwiched therebetween. As viewed from the high-frequency ejector 40, the ejection passage 1019 is disposed on the outer periphery side with the periphery where the gradient magnetic field magnet 31 and the gradient magnetic field magnet 32 are disposed sandwiched therebetween. Through-holes 18 for providing a beam transport system for extracting an ion beam are provided in the side walls of the upper return yoke 4 and the lower return yoke 5.

[0049] The magnetic field distribution generated by the gradient magnetic field magnet 31 can be a distribution in which the magnetic field decreases toward the radial outer side. Alternatively, the magnetic field distribution generated by the gradient magnetic field magnet 32 can be a distribution in which the magnetic field increases toward the radial outer side.

[0050] Further, the gradient magnetic field magnets 31 and 32 can be formed integrally with the lower pole 9. For example, the gradient magnetic field magnets 31 and 32 can be formed by attaching a magnetic body to the surface of the lower pole 9 or by machining the shape of the surface of the lower pole 9. Alternatively, the gradient magnetic field magnets 31 and 32 can be attached to the lower pole 9 by welding, bolt fastening, or the like after being fabricated as separate components.

[0051] Further, the magnetic field in a region from the outer periphery of the upper pole 8 and the lower pole 9 to the side walls of the upper return yoke 4 and the lower return yoke 5 decreases toward the radial outer side. Thus, depending on the degree of decrease in the magnetic field, the gradient magnetic field magnet 31 can not be used.

[0052]

[0053] Figure 4 ​A distribution of the average value of the circumferential magnetic field is shown. The horizontal axis indicates a position on the intersection line of the reference plane 2 and the vertical plane 3, and the vertical axis indicates the average value of the circumferential magnetic field. The average value of the circumferential magnetic field is the average value of the magnetic field over one turn of the circumference of the ion circulating space 10. As shown in Figure 4 the average value of the circumferential magnetic field increases toward the side of the discrete region from the position Yl on the convergence region, and the circumferential average magnetic field becomes the maximum value Bm at the ion injection point Ol. Then, the circumferential average magnetic field monotonically decreases from the ion injection point Ol toward the position Y2 on the discrete region. According to Figure 4 the distribution of the circumferential magnetic average value shown, the beam circulating motion is stabilized by the principle of weak convergence.

[0054] Figure 5 A circumferential magnetic field distribution and a magnetic pole interval of the energy-constant ion beam along the beam orbit are shown. The horizontal axis indicates a position on the beam orbit by the azimuthal angle, and the vertical axis indicates the magnetic field B and the magnetic pole interval d. The azimuthal angle indicates the azimuth from the outside of the center point of the beam orbit. One turn of the azimuthal angle is normalized by π. The origin of the azimuthal angle of 0 and the end point of the azimuthal angle of 2 correspond to the ion extraction action point O4. The position of the azimuthal angle of 1 corresponds to the position on the opposite side of the ion extraction action point O4 from the center point of the beam orbit.

[0055] The magnetic pole interval d is a constant value D in the range of the azimuthal angle of 0 or more and 1-Δ or less and the range of 1+Δ or more and 2 or less. The range of the azimuthal angle corresponds to the region of the non-wide interval region 11 shown in Figure 3 The magnetic pole interval d is a constant value D in the range of the azimuthal angle of 0 or more and 1-Δ or less and the range of 1+Δ or more and 2 or less. The range of the azimuthal angle corresponds to the region of the non-wide interval region 11 shown in Figure 3 The magnetic pole interval d is a constant value D in the range of the azimuthal angle of 0 or more and 1-Δ or less and the range of 1+Δ or more and 2 or less. The range of the azimuthal angle corresponds to the region of the non-wide interval region 11 shown in Figure 5 In the case where the magnetic pole interval d is constant, the magnetic field distribution B0 is also indicated by a dotted line.

[0056] Thus, in the accelerator 100 of the present embodiment, at least one of the upper magnetic pole 8 and the lower magnetic pole 9 is formed so that the magnetic pole interval between the upper magnetic pole 8 and the lower magnetic pole 9 varies when the ion circulating space 10 is observed along the beam orbit. Thereby, the magnetic field variation in space when the ion circulating space 10 is observed along the beam orbit is applied to the ion circulating space 10.

[0057] Typically, the effect of magnetic field variations on an ion beam is evaluated using the BL product, which is the product of the magnitude of the magnetic field and the distance at which the ion beam senses the magnetic field. The radial displacement representing the effect of magnetic field variations on the ion beam is defined as the displacement of the ion beam at the ion extraction point O4 when the BL product is assigned 1 mTm.

[0058] Figure 6 The figure shows the radial displacement of the ion beam at the ion extraction point O4 when a BL product of 1 mTm is locally applied along the beam trajectory. On the horizontal axis, the position where the ion beam is applied with the BL product is represented by the azimuth angle measured from the ion extraction point O4 along the beam travel direction. The vertical axis represents the radial displacement of the ion beam generated at the ion extraction point O4, with the outer radial direction being positive.

[0059] exist Figure 6 In the example shown, when a BL product of 1 mTm is applied at the extraction point O4, the ion beam with energy EL = 70 MeV is radially inwardly displaced by approximately 3.8 mm, and the ion beam with energy EH = 235 MeV is radially inwardly displaced by approximately 2.6 mm at the position of the extraction point O4. Furthermore, when a BL product of 1 mTm is applied on the opposite side of the extraction point O4, which is the center point of the beam trajectory, the ion beam with energy EL = 70 MeV is radially outwardly displaced by approximately 3.8 mm, and the ion beam with energy EH = 235 MeV is radially outwardly displaced by approximately 2.6 mm at the extraction point O4.

[0060] Thus, when a portion of the magnetic field along the beam trajectory is weakened—that is, when the magnetic field ΔB applied to the original magnetic field is positive—the displacement of the ion beam varies depending on the energy of the ion beam and the location of the weakened magnetic field. Specifically, when a portion of the magnetic field is weakened within an azimuth angle of 0 to 0.5 and when a portion of the magnetic field is weakened within an azimuth angle of 1.5 to 2, the lower the energy, the greater the displacement towards the inward side. Moreover, when a portion of the magnetic field is weakened within an azimuth angle greater than 0.5 but less than 1.5, the lower the energy, the greater the displacement towards the outward side.

[0061] Figure 6 This represents the displacement of the ion beam when the magnetic field from the upper magnetic pole 8 to the lower magnetic pole 9 is locally weakened. Therefore, the displacement of the ion beam when the magnetic field from the upper magnetic pole 8 to the lower magnetic pole 9 is locally strengthened. Figure 6the displacement amount of the 70 MeV ion beam is about 3.8 mm radially outward, and the displacement amount of the 235 MeV ion beam is about 2.6 mm radially outward. Also, in the case where the magnetic field is enhanced on the opposite side of the ion extraction operating point O4 from the center point sandwiching the beam orbit, the displacement amount of the 70 MeV ion beam is about 3.8 mm radially inward, and the displacement amount of the 235 MeV ion beam is about 2.6 mm radially inward.

[0062] The range of the azimuth angle exceeding 0.5 and being less than 1.5 corresponds to a region on the center point side of the ion circulating space 10 (magnetic pole center point O2 side) than the center point of the beam orbit. In the following description, the region corresponding to the range of the azimuth angle exceeding 0.5 and being less than 1.5 will be referred to as the first region. Also, the range of the azimuth angle being 0 or more and 0.5 or less and the range of the azimuth angle being 1.5 or more and 2 or less correspond to a region on the ion extraction operating point O4 side than the center point of the beam orbit. In the following description, the region corresponding to the range of the azimuth angle being 0 or more and 0.5 or less and the range of the azimuth angle being 1.5 or more and 2 or less will be referred to as the second region.

[0063] According to the above description, in the case where the magnetic field is locally weakened in the first region, or in the case where the magnetic field is locally enhanced in the second region, at the ion extraction operating point O4, the smaller the energy, the greater the displacement amount toward the outside.

[0064] In the present embodiment, the magnetic field is weakened in the first region, or the magnetic field is enhanced in the second region, so that at the position where the high-frequency ejector 40 is disposed (the ion extraction operating point), the smaller the energy of the ion beam, the greater the displacement amount toward the outside.

[0065] That is, the evaluation value of the magnetic pole interval along the beam orbit in the first region is greater than the evaluation value of the magnetic pole interval along the beam orbit in the second region. Here, the evaluation value of the magnetic pole interval is a value for evaluating the size of the magnetic pole interval. The greater the evaluation value, the more the magnetic pole interval along the beam orbit is evaluated to be greater in total. Also, the evaluation value can be defined as a value in which the greater the value of the first region, the greater the outside displacement effect of the ion beam (the effect of the ion beam of low energy being displaced toward the outside at the ion extraction operating point). The evaluation value of the magnetic pole interval along the beam orbit is, for example, a statistical value such as the average value, the square root mean, the median, the mode, or the like of the magnetic pole interval along the beam orbit.

[0066] With such a configuration of the upper magnetic pole 8 and the lower magnetic pole 9, a spatial variation of the magnetic field when the ion circulating space 10 is observed along the beam orbit can be brought about. This magnetic field variation is a variation of the spatial magnetic field that displaces the ions in such a manner that the smaller the energy of the ions, the greater the displacement amount of the ions toward the outside direction at the ion extraction operating point O4.

[0067] The magnetic field evaluation value along the beam orbit in the first region is smaller than the magnetic field evaluation value along the beam orbit in the second region. Here, the magnetic field evaluation value is a value for evaluating the magnitude of the magnetic field in the ion orbiting space 10. The smaller the magnetic field evaluation value, the greater the magnetic field integrated along the beam orbit from the upper magnetic pole 8 toward the lower magnetic pole 9 is evaluated. In addition, the magnetic field evaluation value can also be defined as a value in which the smaller the value of the first region, the greater the effect of the lateral displacement of the ion beam. The magnetic field evaluation value along the beam orbit is, for example, a statistical value such as the average value, the square root mean, the median, or the mode of the magnetic field along the beam orbit.

[0068] With such a configuration and magnetic field distribution, the smaller the energy, the greater the amount of displacement of the beam orbit to the outside at the ion extraction action point O4. Thus, for an ion beam having a relatively small energy, the time required to extract the ion beam is shortened, and the time response characteristic at the time of extracting the ion beam is good.

[0069] Hereinafter, the principle of extracting the ion beam from the accelerator 100 will be described based on a physical phenomenon. The amount of displacement δ of the ion beam is represented by the following (Equation 1).

[0070] [Equation 1]

[0071]

[0072] Here, β represents the horizontal direction betatron amplitude of the ion beam, v represents the horizontal direction betatron vibration frequency, s and s0 represent the positions on the beam orbit, and ψ(s) - ψ(s0) represents the phase difference of the betatron vibration. The horizontal direction betatron amplitude β, the beam orbit, and the phase ψ of the betatron vibration depend on the energy of the ion beam.

[0073] In the present embodiment, the gradient magnetic field based on the gradient magnetic field magnets 31 and 32 acts on the ion beam, and the ion beam is extracted using the so-called 2 / 2 resonance of the horizontal direction of the beam. At this time, the horizontal direction betatron vibration frequency v can be a value close to 1. In the case where the horizontal direction betatron vibration frequency v is 1, the phase of the betatron vibration increases by approximately 2π during one revolution of the ion beam.

[0074] In the case where the horizontal direction betatron vibration frequency v is 1, when s and s0 are approximately shifted by half a period, the phase difference ψ(s) - ψ(s0) is approximately π, and the argument of the cosine function cos is approximately 0. In addition, when s and s0 coincide, the argument of the cosine function cos is approximately π. In correspondence therewith, in the case where the argument of the cosine function cos is 0, the magnetic field evaluation value is the maximum value. In the case where the argument of the cosine function cos is π, the magnetic field evaluation value is the minimum value. Figure 6In this case, the displacement amount of the ion beam differs depending on the energy, and peaks appear at the azimuth angles of 0 and 1. In the case where the ion beam is extracted using 2 / 2 resonance, at the position where the azimuth angle is 0, a high-frequency electric field (perturbation electric field) is generated by a high-frequency electric field generator such as the high-frequency injector 40, and the displacement of the ion beam is caused, whereby the ion beam is efficiently extracted from the accelerator 100.

[0075] The specific operation of the accelerator 100 according to the present embodiment will be described. The ions generated by the ion source 1003 are incident on the reference plane 2 through the through-hole 24. The ions are accelerated by the high-frequency acceleration cavity 1037, and perform a cyclotron motion while increasing the orbit radius, and reach the orbit through the high-frequency injector 40. While the ions perform the cyclotron motion while increasing the orbit radius, the energy of the ions increases.

[0076] At the time when the energy of the ions reaches the target energy, the high-frequency electromagnetic field excited in the high-frequency acceleration cavity 1037 is cut off, and a high-frequency electric field is excited from the high-frequency injector 40. Thereby, the amplitude of the horizontal direction ESR vibration becomes large, and the ion beam passes through the regions where the gradient magnetic field magnets 31 and 32 located radially outward of the high-frequency injector 40 act. Further, the 2 / 2 resonance described above is caused, and the ion beam diverges in the horizontal direction to reach the extraction passage 1019, and the ion beam is separated from the cyclotron orbit through the extraction passage 1019. The ion beam separated from the cyclotron orbit is extracted to the outside of the accelerator 100 through the through-hole 18.

[0077] In the present embodiment, the magnetic field is not constant along the beam orbit, as shown in FIG. 1, and in the wide gap region 11, the magnetic field is reduced compared to the regions other than the wide gap region 11. Thereby, at the ion extraction operation point O4 where the high-frequency injector 40 is disposed, the interval of the beam orbits of the ion beams having different energies becomes narrow. Figure 5

[0078] Therefore, for the ion beam having a relatively small energy, the amplitude of the ESR vibration required to extract the ion beam becomes small, and the time from when the high-frequency voltage is applied to the high-frequency injector 40 to when the ion beam is extracted becomes short. Thereby, the timing when the ion beam is extracted can be controlled with high precision.

[0079] In the present embodiment, the wide gap region 11 is provided in the ion cyclotron space 10 sandwiched by the upper magnetic pole 8 and the lower magnetic pole 9. The accelerator 100 can not be provided with the wide gap region 11, but can be configured to reduce the magnetic field using the trimming coil 53.

[0080] In addition, the embodiment in which the wide gap region 11 is provided in the first region is shown in the above description. In the ion cyclotron space 10, a narrow gap region can be provided in the second region. The narrow gap region is a region in which the pole gap is smaller than the surrounding regions.

[0081] ​<Second Embodiment>

[0082] Figure 7 An accelerator 102 of a second embodiment of the present application is shown. Figure 7 A plan view of the accelerator 102 is shown in FIG. 12. The accelerator 102 is cut by the reference plane 2, and is observed from above the lower return yoke 5 side. In the lower return yoke 5, recesses 121a, 121b, 121c, and 121d are formed. The recesses 121a, 121b, 121c, and 121d are regions that are recessed downward. By the formation of the recesses, protrusions 122a, 122b, 122c, and 122d are formed in the lower return yoke 5. The protrusions 122a, 122b, 122c, and 122d are regions that protrude upward with respect to the deepest portions of the recesses as reference.

[0083] The recesses and the protrusions can also be provided over regions occupied by the beam orbit corresponding to the energy of the extracted object. That is, the recesses and the protrusions can also be provided near the outer periphery of the ion circulating space 10.

[0084] When the lower return yoke 5 is observed along the beam orbit, the recesses and the protrusions are alternately arranged. In the upper return yoke 4, recesses are also formed in regions that are opposed to the recesses 121a, 121b, 121c, and 121d formed in the lower return yoke 5. Further, in the upper return yoke 4, protrusions are also formed in regions that are opposed to the protrusions 122a, 122b, 122c, and 122d formed in the lower return yoke 5.

[0085] The recesses and the protrusions can be provided in either one of the upper return yoke 4 and the lower return yoke 5, or both of the upper return yoke 4 and the lower return yoke 5.

[0086] Further, the region in which the ejection passage 1019 is provided corresponds to the recesses of the upper return yoke 4 or the recesses of the lower return yoke 5.

[0087] Thus, in the accelerator 102 of the present embodiment, when the ion circulating space 10 is observed along the beam orbit, at least one of the upper magnetic pole 8 and the lower magnetic pole 9 is formed so that the magnetic pole interval between the upper magnetic pole 8 and the lower magnetic pole 9 varies. Thus, the accelerator 102 of the present embodiment is configured to apply a spatial variation of the magnetic field when the ion circulating space 10 is observed along the beam orbit. That is, at least one of the upper magnetic pole 8 and the lower magnetic pole 9 is alternately formed with recesses and protrusions on a surface facing the ion circulating space 10 along the beam orbit.

[0088] In the following description, a region in which a concave portion belonging to the upper return yoke 4 and a concave portion belonging to the lower return yoke 5 face each other is referred to as a valley region. In addition, a region in which a convex portion belonging to the upper return yoke 4 and a convex portion belonging to the lower return yoke 5 face each other is referred to as a peak region. In the valley region, the pole pitch is larger than in the peak region, and thus the magnetic field is smaller than in the peak region.

[0089] The high-frequency acceleration cavity 1037 can be provided in the valley region. In the present embodiment, the high-frequency acceleration cavity 1037 is provided in the valley region sandwiched by the concave portion 121c formed in the upper return yoke 4 and the concave portion 121c formed in the lower return yoke 5. In the present embodiment, the range of the azimuth angle of the ion beam passing through the high-frequency acceleration cavity 1037 is narrower than in the first embodiment. Thus, in the present embodiment, the frequency of the high-frequency electromagnetic field excited in the high-frequency acceleration cavity 1037 is higher than in the first embodiment.

[0090] The trim coils 54 and 55 are provided in the peak regions on both sides of the outside of the high-frequency acceleration cavity 1037. Thus, the trim coils 54 and 55 are closer to the reference plane 2 than in the case where the trim coils are provided in the valley region formed by the concave portion 121c. Thus, the magnetic motive force emitted from each of the trim coils 54 and 55 for adjusting the beam orbit is lower than in the case where the trim coils are provided in the valley region formed by the concave portion 121c.

[0091] The trim coils 51 and 52 are disposed in the convex portions 122d. By disposing the trim coils 51 and 52 in the peak regions formed by the convex portions 122d, the trim coils 51 and 52 are closer to the reference plane 2 than in the case where the trim coils are disposed in the valley region. Thus, the magnetic motive force emitted from each of the trim coils 51 and 52 for adjusting the beam orbit is lower than in the case where the trim coils are provided in the valley region.

[0092] Figure 8 A distribution of the magnetic field along the beam orbit is shown. The horizontal axis represents the azimuth angle along the beam orbit, and the vertical axis represents the magnetic field B. The distribution of the magnetic field is based on the case where the pole pitch in each of the peak regions based on the convex portions 122b and 122c is larger than the pole pitch in each of the peak regions based on the convex portions 122a and 122d. Thus, the magnetic field in each of the peak regions based on the convex portions 122b and 122c is smaller than the magnetic field in each of the peak regions based on the convex portions 122a and 122d.

[0093] By making the magnetic field in each peak region based on the convex portions 122b and 122c smaller than the magnetic field in each peak region based on the convex portions 122a and 122d, the energy is smaller at the position of the high-frequency ejector 40, and the amount of displacement to the radially outer side of the beam orbit is larger. Thus, for an ion beam having relatively small energy, the amplitude of the betatron vibration required to extract the ion beam is smaller, and the time from when the high-frequency voltage is applied to the high-frequency ejector 40 to when the ion beam is extracted is shorter. Therefore, the timing at which the ion beam is extracted can be controlled with high precision.

[0094] In the accelerator 102, the concave portions and the convex portions are alternately arranged along the beam orbit, and the strength of the magnetic field alternately appears when viewed along the beam orbit. Thus, the betatron vibration of the ion beam in the up-and-down direction is stabilized, and the divergence of the ion beam in the up-and-down direction is suppressed.

[0095] In addition, the emission passage 1019 is disposed in the valley region, and thus the magnetic field in the emission passage 1019 is weakened. Thus, under the condition that the magnetic motive force of the electromagnet provided in the emission passage 1019 is constant, the number of ions extracted through the emission passage 1019 increases.

[0096] Further, instead of adjusting the pole gap, a structure in which the magnetic field is weakened by trimming the coil 54 or 55 can be employed. In addition, the embodiment in which the high-frequency ejector 40 is disposed at the ion extraction operation point O4 is shown in the above description. A disturbance magnetic field generator that generates a disturbance magnetic field can be disposed at or near the ion extraction operation point O4. The disturbance magnetic field generator applies a disturbance magnetic field to the ion beam to increase the amplitude of the betatron vibration of the ion beam in the horizontal direction. The disturbance magnetic field generator can be configured by a plurality of coils as shown in Patent Literature 2.

[0097] Next, a particle beam therapy system using the accelerator 100 or 102 of each of the above-described embodiments will be described. Figure 9 The structure of a particle beam therapy system 1001 is shown. The particle beam therapy system 1001 is disposed on the floor of a building (omitted from the drawing). The particle beam therapy system 1001 includes an ion beam generating device 1002, a beam transport system 1013, a rotating gantry 1006, an irradiation device 1007, and a control system 1065.

[0098] The ion beam generating device 1002 has an ion source 1003 and an accelerator 100 or 102 (hereinafter, the accelerator 100 or 102 is referred to as an accelerator 10X) connected to the ion source 1003.

[0099] A coil excitation power source 1057 is connected to the coil 6 (see FIG. 2) provided in the accelerator 10X via a coil lead 1022. Figure 2 The coil excitation power source 1057 flows current to the coil 6.

[0100] The high-frequency power source 1036 inputs an electromagnetic field to the high-frequency acceleration cavity 1037 provided in the accelerator 10X through the waveguide 1010, and causes a high-frequency electric field that accelerates the ion beam to be excited between an electrode connected to the high-frequency acceleration cavity 1037 and a ground electrode. In the accelerator 10X, the resonance frequency of the electromagnetic field excited in the high-frequency acceleration cavity 1037 is modulated in correspondence with the energy of the ion beam. In order to modulate the frequency, the inductance or the electrostatic capacity can be adjusted. The adjustment method of the inductance or the electrostatic capacity can use a publicly known method. For example, in the case of adjusting the electrostatic capacity, a variable capacitor is connected to the high-frequency cavity, and the electrostatic capacity of the variable capacitor is controlled.

[0101] The ejection passage power source 1082 is connected to the electromagnet provided in the ejection passage 1019. The ejection passage power source 1082 supplies a current to the electromagnet provided in the ejection passage 1019, thereby adjusting the ion beam that reaches the ejection passage 1019 and transporting the ion beam to the beam transport system 1013. The beam current measuring device 1098 includes the moving device 1017 and the position detector 1039.

[0102] The beam transport system 1013 has a beam path 1048 to the irradiation device 1007. The beam transport system 1013 further has a plurality of quadrupole electromagnets 1046, a deflection electromagnet 1041, a plurality of quadrupole electromagnets 1047, a deflection electromagnet 1042, quadrupole electromagnets 1049, 1050, deflection electromagnets 1043 and 1044.

[0103] In the beam path 1048, from the accelerator 10X toward the irradiation device 1007, the plurality of quadrupole electromagnets 1046, the deflection electromagnet 1041, the plurality of quadrupole electromagnets 1047, the deflection electromagnet 1042, the quadrupole electromagnets 1049, 1050, the deflection electromagnets 1043 and 1044 are sequentially arranged.

[0104] A part of the beam path 1048 provided in the beam transport system 1013 is provided in the rotary gantry 1006. The deflection electromagnet 1042, the quadrupole electromagnets 1049, 1050, and the deflection electromagnets 1043, 1044 provided in the beam transport system 1013 are also provided in the rotary gantry 1006. The beam path 1048 is connected to the ejection passage 1019 provided in the accelerator 10X.

[0105] The rotary gantry 1006 is configured to be rotatable around the rotation axis 1045, and is a rotation device that causes the irradiation device 1007 to revolve around the rotation axis 1045.

[0106] The irradiation device 1007 is provided with two scanning electromagnets 1051, 1052, a beam position monitor 1053, and a radiation dose monitor 1054. These scanning electromagnets 1051, 1052, the beam position monitor 1053, and the radiation dose monitor 1054 are arranged along the central axis of the irradiation device 1007, i.e., the beam axis. The scanning electromagnets 1051, 1052, the beam position monitor 1053, and the radiation dose monitor 1054 are arranged in a housing (not shown) of the irradiation device 1007.

[0107] The beam position monitor 1053 and the radiation dose monitor 1054 are arranged downstream of the scanning electromagnets 1051, 1052. The scanning electromagnets 1051, 1052 deflect the ion beam and scan the ion beam in mutually orthogonal directions in a plane perpendicular to the central axis of the irradiation device 1007. The beam position monitor 1053 measures the passing position of the irradiated ion beam. The radiation dose monitor 1054 measures the radiation dose of the irradiated ion beam.

[0108] The irradiation device 1007 is mounted to the rotating gantry 1006 and arranged downstream of the deflection electromagnet 1044.

[0109] On the downstream side of the irradiation device 1007, a treatment table 1055 on which a patient 1056 lies is arranged in opposition to the irradiation device 1007.

[0110] The control system 1065 has a central control device 1066, an accelerator, a transport system control device 1069, a scanning control device 1070, a rotation control device 1088, and a database 1072. The central control device 1066 has a central processing unit (CPU) 1067 and a memory 1068 connected to the CPU 1067. The accelerator, the transport system control device 1069, the scanning control device 1070, the rotation control device 1088, and the database 1072 are connected to the CPU 1067 in the central control device 1066.

[0111] The particle ray therapy system 1001 further has a treatment planning device 1073 connected to the database 1072. In the particle ray therapy system 1001, information indicating the irradiation energy, the irradiation angle, and the like of the particle ray is made into a treatment plan by the treatment planning device 1073 before the particle ray is irradiated, and the irradiation is performed based on the treatment plan.

[0112] The CPU 1067 of the central control device 1066 reads various action control programs related to irradiation of each device constituting the particle ray therapy system 1001 from the treatment plan stored in the database 1072. The CPU 1067 of the central control device 1066 executes the read programs and outputs an instruction via the accelerator, the transport system control device 1069, the scanning control device 1070, and the rotation control device 1088, thereby controlling the actions of each device in the particle ray therapy system 1001.

[0113] Further, the programs that execute the control processing can be aggregated into one program, can be divided into a plurality of programs respectively, or can be a combination thereof. In addition, a part or all of the programs can be implemented by a dedicated hardware, or can be modularized. Also, the various programs can be installed in each computer through a program distribution server or an external storage medium.

[0114] In addition, each control device can be connected by a wired or wireless network by separate independent devices, or can be integrated into two or more.

[0115] With such a configuration, in the particle ray therapy system 1001, ions injected from the ion source 1003 to the accelerator 1010 are accelerated by the accelerator 1010. The ion beam taken out from the accelerator 1010 is transported to the irradiation device 1007 by the beam transport system 1013. The irradiation device 1007 irradiates the ion beam to the affected part of the patient 1056.

[0116] Symbol Explanation

[0117] 1 - main magnetic field magnet, 2 - reference plane, 3 - vertical plane, 4 - upper return yoke, 5 - lower return yoke, 6 - coil, 7 - vacuum vessel, 8 - upper pole, 9 - lower pole, 10 - ion circulating space, 11 - wide gap region, 12 - ion incident axis, 13 - pole center axis, 15, 16, 18, 24 - through hole, 31, 32 - gradient magnetic field magnet, 40 - high frequency injector, 51, 52, 53, 54, 55 - trimming coil, 121a, 121b, 121c, 121d - recess, 122a, 122b, 122c, 122d - protrusion, 126, 127 - beam orbit, 100, 102, 10X - accelerator, 1001 - particle radiotherapy system, 1002 - ion beam generating device, 1003 - ion source, 1006 - rotating gantry, 1007 - irradiation device, 1010 - waveguide, 1017 - moving device, 1019 - ejection passage, 1022 - coil lead wire, 1036 - high frequency power supply, 1037 - high frequency accelerating cavity, 1039 - position detector, 1041-1044 - deflection electromagnet, 1045 - rotating shaft, 1046, 1047, 1049, 1050 - quadrupole electromagnet, 1048 - beam path, 1051, 1052 - scanning electromagnet, 1053 - position monitor, 1054 - radiation dose monitor, 1055 - treatment table, 1056 - patient, 1057 - power supply for coil excitation, 1065 - control system, 1066 - central control device, 1067 - CPU, 1068 - memory, 1069 - accelerator, transport system control device, 1070 - scanning control device, 1072 - database, 1073 - treatment planning device, 1082 - power supply for ejection passage, 1088 - rotating control device, 1098 - beam current measuring device.

Claims

1. An accelerator characterized by comprising: an upper magnetic pole and a lower magnetic pole that sandwich an ion circulating space in which ions perform a circulating motion, the upper magnetic pole and the lower magnetic pole being configured so that a magnetic field variation in space is applied when the ion circulating space is observed along an ion beam orbit, the magnetic field variation being such that a magnetic field evaluation value along the ion beam orbit in a region on a center point side of the ion circulating space with respect to a center point of the ion beam orbit is smaller than a magnetic field evaluation value along the ion beam orbit in a region on an ion extraction operation point side with respect to the center point of the ion beam orbit, the magnetic field variation being such that the more an ion is low in energy, the larger a displacement amount of the ion at the ion extraction operation point in an outward direction is.

2. The accelerator according to claim 1, characterized by comprising a trimming coil that is provided to at least one of the upper magnetic pole side and the lower magnetic pole side with respect to a reference plane that is sandwiched by the upper magnetic pole and the lower magnetic pole, and that applies the magnetic field variation.

3. The accelerator according to claim 1 or 2, characterized in that at least one of the upper magnetic pole and the lower magnetic pole is formed so that a magnetic pole interval between the upper magnetic pole and the lower magnetic pole varies when the ion circulating space is observed along the ion beam orbit.

4. An accelerator characterized by comprising: an upper magnetic pole and a lower magnetic pole that sandwich an ion circulating space in which ions perform a circulating motion, at least one of the upper magnetic pole and the lower magnetic pole being formed so that a magnetic pole interval between the upper magnetic pole and the lower magnetic pole varies when the ion circulating space is observed along an ion beam orbit, an evaluation value of the magnetic pole interval along the ion beam orbit in a region on a center point side of the ion circulating space with respect to a center point of the ion beam orbit being larger than an evaluation value of the magnetic pole interval along the ion beam orbit in a region on an ion extraction operation point side with respect to the center point of the ion beam orbit.

5. The accelerator according to claim 4, characterized in that the upper magnetic pole and the lower magnetic pole are configured so that a magnetic field variation in space is applied when the ion circulating space is observed along an ion beam orbit, the magnetic field variation being such that the more an ion is low in energy, the larger a displacement amount of the ion at the ion extraction operation point in an outward direction is.

6. The accelerator according to claim 4 or 5, characterized in that a wide interval region in which the magnetic pole interval is larger than a peripheral region is formed in a region on a center point side of the ion circulating space with respect to a center point of the ion beam orbit.

7. The accelerator according to claim 4 or 5, characterized in that a narrow interval region in which the magnetic pole interval is smaller than a peripheral region is formed in a region on an ion extraction operation point side with respect to the center point of the ion beam orbit.

8. The accelerator according to claim 4 or 5, characterized in that in at least one of the upper magnetic pole and the lower magnetic pole, a surface that faces the ion circulating space is alternately formed with a recess and a protrusion along the ion beam orbit. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 9. The accelerator according to claim 8, wherein a trimming coil is provided at least one of the upper magnetic pole side and the lower magnetic pole side than a reference plane sandwiched by the upper magnetic pole and the lower magnetic pole, and at a position corresponding to the convex portion.

10. The accelerator according to claim 8, wherein a high-frequency acceleration cavity is provided at a position corresponding to the recess formed in at least one of the upper magnetic pole and the lower magnetic pole.

11. The accelerator according to claim 8, wherein an emission passage for extracting an ion beam by an electromagnet is provided at a position corresponding to the recess formed in at least one of the upper magnetic pole and the lower magnetic pole.

12. The accelerator according to any one of claims 1, 2, and 4, wherein a high-frequency electric field generator is provided at the ion extraction action point.

13. The accelerator according to any one of claims 1, 2, and 4, wherein a disturbing magnetic field generator is provided at the ion extraction action point.

14. A particle ray therapy system, comprising: the accelerator according to any one of claims 1 to 13; a beam transport system that transports the ion extracted from the accelerator; and an irradiation device that irradiates the ion transported by the beam transport system to a patient. ​

Images