CN115671576A - BNCT-related low-energy charged particle beam transport system and charged particle beam transport method - Google Patents

Abstract

The invention relates to a BNCT-related low-energy charged particle beam transport system and a BNCT-related charged particle beam transport method; the accelerator emits a low-energy charged particle beam of 5MeV or less, and the beam transport line transports the charged particle beam emitted from the accelerator. The target contains lithium and generates a neutron beam by being irradiated with the charged particle beam transported by the beam transport line. The energy reducing system reduces the energy of the neutron beam generated by the target to the thermal neutron range. The beam condensing lens is positioned inside the beam transport line, and includes a predetermined number of quadrupole electromagnets provided along the charged particle beam irradiation direction from the upper end of the charged particle beam and a predetermined number of octapole electromagnets provided along the charged particle beam irradiation direction from the rear end position quadrupole electromagnet. The focusing lens control part controls the magnetism of the quadrupole electromagnet and the octopole electromagnet, so that the beam profile of the charged particle beam in the radial direction is amplified and is uniform.

Description

BNCT-related low-energy charged particle beam transport system and charged particle beam transport method

Technical Field

The invention relates to a BNCT-related low-energy charged particle beam transport system and a BNCT-related charged particle beam transport method.

Background

Boron Neutron Capture Therapy (Boron Neutron Capture Therapy) is one type of cancer radiation Therapy. Boron neutron capture therapy (hereinafter, referred to as "BNCT") utilizes the property that boron compounds can selectively concentrate in cancer cells, and neutron irradiation is applied thereto¹⁰ B（n，α）⁷ Li nuclear reactionThe alpha particles and lithium nuclei that should be generated destroy cancer cells. Since the radiation range of alpha particles and lithium nuclei is comparable to the size of cells, the therapy has the advantage of selectively destroying only cancer cells without damage to normal cells.

The BNCT profile is illustrated below: first, as a method for generating neutrons, neutrons are generated mainly by using an accelerator in recent years, in addition to neutrons generated by a nuclear reactor. The following four types of nuclear reactions are more common: firstly, the⁹ Be（p，n）⁹ B reaction, II⁷ Li（p，n）⁷ Be reaction, III² H(² H,n)³ He reaction, IV³ H（² H,n）⁴ He reaction. For charged particle energies in the four reactions, the first nuclear reaction uses beryllium as the target, with energies up to 30MeV. The second nuclear reaction takes lithium as a target, the energy of the charged particles is about 3MeV, and the third nuclear reaction and the fourth nuclear reaction take hydrogen as a target, so that the energy of the nuclear fusion reaction is lower and is only 100keV. The acceleration system of the charged particles includes a cyclotron, an electrostatic accelerator, a linear accelerator, and the like. As described later, the only BNCT apparatus approved by the province of the great health and labor in Japan uses a cyclotron to generate neutrons by using a first nuclear reaction. In addition to the accelerator, BNCT devices typically include a beam transport system (also known as a beam line, beam line) that delivers charged particles produced by the accelerator to the neutron generating target, and a de-energizing system that decelerates high-energy neutrons generated by the target into the thermal neutron range.

Currently, a wide variety of techniques are being developed in connection with BNCT. For example, japanese patent application laid-open No. 2018-161449 (patent document 1) discloses a neutron energy-reducing irradiation device including an energy-reducing portion, a reflecting portion, and a collimator portion (collimater). The energy reducing part reduces energy of the charged particle beam irradiated to the neutron source to generate the neutron beam, and the reflecting part reflects the neutron beam around the outside of the energy reducing part. The collimator part shapes the radial profile of the neutron beam after being reduced by the energy reducing part, and is also provided with a spacing part and a pipe orifice part. The spacer portion is provided at a lower end of the energy decreasing portion in the charged particle beam irradiation direction, and a small hole portion having a smaller diameter is provided in the irradiation direction. The nozzle part is arranged at the lower end of the spacing part along the irradiation direction, protrudes from the periphery of the small hole part to the irradiation direction, and is provided with a through hole at the center. Further, the nozzle portion contains a reflective material forming an inner wall of the through hole and a shielding material surrounding the reflective material. In this way, high intensity and precise irradiation of the neutron beam can be achieved.

Japanese patent laying-open No. 2020-146119 (patent document 2) discloses a neutron capture therapy system including an accelerator, a target, a beam transport line, a 1 st current detection section, a 2 nd current detection section, and a non-overlapping section. The accelerator emits a charged particle beam, and the target is irradiated with the charged particle beam to generate a neutron beam. The 1 st current detection part is arranged in the beam transport line, is in an insulation state with the inner wall of the beam transport line and is responsible for detecting the current value of the charged particle beam. The 2 nd current detection part is arranged in the beam current transmission line, is positioned at the lower end of the 1 st current detection part, is in an insulation state with the inner wall of the beam current transmission line and is responsible for detecting the current value of the charged particle beam. The non-overlapping portion is a portion where the 1 st current detection portion and the 2 nd current detection portion are not overlapped with the 1 st current detection portion when the 1 st current detection portion and the 2 nd current detection portion are viewed from a line of sight parallel to the extending direction of the beam transport line. In this way, the reliability of detecting the position abnormality of the charged particle beam irradiation target is improved.

Meanwhile, there are many related studies on the BNCT beam transport line. For example, non-patent document 1 (Yosuke Yuri, et al, "uniformity of the transform beam profile by means of the means of nonlinear focusing method", phys. Rev. St accel.Beams 10, 104001 Published 29 October 2007) discloses that, through simulation calculations, an asymmetrically distributed beam can be converted into a uniformly distributed beam by nonlinearly focusing a charged particle beam (beam) in a beam transport line using hexapole and octapole electromagnets.

In addition, non-patent document 2 (Shin-ichiro Meigo, et al, "Two-parameter model for optimizing target beam distribution with an octapole map", phys. Rev. Accel. Beams23, 062802 Published 23 June 2020) mentions that the beam profile (beam profile) in the beam transport system can be optimally adjusted by using an octapole electromagnet based on nonlinear optics based on comparison of the simulation calculation result with the actual experiment result.

Patent documents: (1) Japanese patent application laid-open No. 2018-161449; (2) JP-A2020-146119.

Non-patent documents: (1) Yosuke Yuri, et al, "uniformity of the transform beam profile by means of the non-linear focusing method", phys. Rev. ST Accel.Beams 10, 104001 public 29 October 2007;

（2）Shin—ichiro Meigo，et al.，“Two—parameter model for optimizing target beam distribution with an octupole magnet”,Phys. Rev. Accel. Beams 23, 062802 Published 23 June 2020。

disclosure of Invention

The problems to be solved by the present invention are as follows:

japanese approved medical equipment for BNCT in 2020 primarily irradiates beryllium targets with a higher energy (e.g., 30 MeV) proton beam emitted from a cyclotron⁹ Be（p，n）⁹ The B-response produces a neutron beam that can be used for BNCT treatment. Here, to promote more efficient neutron beam interaction with the patient¹¹ B to carry out the reaction, it is necessary to reduce the energy of the neutron beam to the range of the thermal neutron beam. This problem can be solved by the technique described inpatent document 1.

Meanwhile, the accelerators for BNCT have become more compact in recent years, and can generate a proton beam with low energy. Therefore, the development of medical devices for BNCT using an ejected low energy proton beam accelerator is also rapidly progressing.

It is assumed here that the target irradiated with a low-energy proton beam is lithium, and the above-mentioned second type is used⁷ Li（p，n）⁷ Be nuclear reaction. In this reaction, although the energy of the proton beam can be usedLow energy below 5MeV, but the melting point of lithium contained in the target is only 179 ℃, which is lower compared to the beryllium melting point (1278 ℃) used in conventional targets irradiated with high energy proton beams. Meanwhile, in order to generate the amount of neutrons required for BNCT, a large current of 10mA is required for the amount of proton lines. When a proton beam of 10mA × 5mev=50kw heating value is concentrated in a narrow area of a lithium target, lithium contained in the target is evaporated. In particular, in recent years, the above problem has become more remarkable as the thickness of the target becomes thinner. In order to solve the problem, it is necessary to control the radial area of a proton beam emitted from an accelerator to be uniformly and uniformly amplified when the proton beam passes through the inside of a beam transport line, and then transport the proton beam to a target for irradiation.

The above problems cannot be solved by the techniques described inpatent document 2 andnon-patent documents 1 and 2.

In order to solve the above problems in the prior art, a primary object of the present invention is to provide a system and a method for transporting a charged particle beam with low energy, which can transport a charged particle beam with medium-low energy and large current uniformly in a wide range, in connection with BNCT.

In order to realize the purpose, the invention adopts the technical scheme that:

the invention relates to a BNCT-related low-energy charged particle beam transport system, which comprises an accelerator, a beam transport line, a target, an energy reducing system, a cluster lens and a cluster lens control part. The accelerator emits a low energy beam of charged particles below 5 MeV. The beam transport line transports the charged particle beam emitted by the accelerator. The charged particle beam transported by the beam transport line irradiates a target containing lithium to generate a neutron beam. The energy reducing system reduces the energy of the neutron beam generated by the target to be in a thermal neutron range. The collecting lens is composed of quadrupole electromagnets and octupole electromagnets arranged in the beam transport line, wherein, a predetermined number of quadrupole electromagnets are arranged along the irradiation direction of the charged particle beam from the front end position of the charged particle beam; a predetermined number of octupole electromagnets are provided along the charged particle beam irradiation direction from the front end position of the charged particle beam. The beam profile (beam profile) in the radial direction of the charged particle beam is enlarged and made uniform by the beam lens control part by controlling the magnetic fields of the quadrupole electromagnet and the octupole electromagnet.

The invention relates to a BNCT-related low-energy charged particle beam transport method, which relates to a charged particle beam transport method of a charged particle beam transport system comprising the accelerator, a beam transport line, a target, an energy reducing system and a cluster lens, and also comprises a cluster lens control project. The cluster lens control process (step) corresponds to the cluster lens control section.

The invention relates to a BNCT-related low-energy charged particle beam transport system and a BNCT-related charged particle beam transport method, namely a BNCT-related low-energy charged particle beam transport system and a BNCT-related charged particle beam transport method.

The invention has the beneficial effect that the low-energy large-current charged particle beams in BNCT can be transported uniformly and controllably in a wider range.

Drawings

FIG. 1 is a schematic diagram of a low energy charged particle beam transport system associated with BNCT provided in accordance with the present invention;

FIG. 2 is a flowchart illustrating the practical operation sequence of the charged particle beam transporting method related to BNCT provided by the present invention;

FIG. 3 is a cross-sectional view of a quadrupole electromagnet according to an embodiment of the present invention, as viewed from a charged particle beam irradiation direction;

FIG. 4 is a cross-sectional view of an octopole electromagnet according to an embodiment of the present invention, viewed from the charged particle beam irradiation direction;

FIG. 5 is a schematic view of a first basic configuration of a cluster lens according to an embodiment of the present invention;

FIG. 6 is a schematic view of a second basic configuration of a cluster lens according to an embodiment of the present invention;

FIG. 7 is one of schematic views of a first application configuration of a cluster lens relating to an embodiment of the present invention;

FIG. 8 is a second schematic view of a first application configuration of a cluster lens according to an embodiment of the present invention;

fig. 9 is one of schematic diagrams of a second application configuration of a cluster lens related to the embodiment of the present invention;

FIG. 10 is a second schematic view of a second application configuration of a cluster lens according to an embodiment of the present invention;

fig. 11, 12 and 13 are schematic diagrams illustrating the simulation calculation result of the initial beam profile (beam profile) in the case of adopting the first basic configuration of the cluster lens;

fig. 14, 15 and 16 are schematic diagrams illustrating the simulation calculation results of beam profile (beam profile) after passing through the cluster lens under the condition of adopting the first basic construction of the cluster lens;

fig. 17, 18 and 19 are schematic diagrams illustrating simulation calculation results of an initial beam profile (beam profile) in the case of adopting a second basic configuration of a cluster lens;

fig. 20, 21 and 22 are schematic diagrams illustrating simulation calculation results of beam profiles (beam profiles) after passing through the cluster lens under the condition of adopting the cluster lens of the second basic structure.

1. A low energy high current charged particle beam transport system for BNCT; 10. an accelerator; 11. a beam transport line; 12. a target; 13. an energy reduction system; 14. a cluster lens; 15. a control section; 101. an accelerator control section; 102. a cluster lens control section; 14a, a four-pole electromagnet at the front end position; 14b, a middle-end position four-pole electromagnet; 14c, a rear end position quadrupole electromagnet; 14d, (front end) eight-pole electromagnet; 14e, an eight-pole electromagnet at the rear end position; 14f, 14g, 1 or more quadrupole electromagnets can be added properly; C. a charged particle beam; n, neutron beam; t0, the overall distance from the accelerator 10 to the target 12; t, the base distance from the accelerator 10 to the target 12; s101, irradiating a charged particle beam; s102, controlling a magnetic field; x1, the length of the front end position quadrupole electromagnet 14 a; x2, length of the middle-end position quadrupole electromagnet 14 b; x3, length of the rear end position quadrupole electromagnet 14 c; x4, length of the (front) octopole electromagnet 14 d; x5, the length of the rear end position octopole electromagnet 14 e; d1, a first interval is formed between the middle-end position four-pole electromagnet 14b and the front-end position four-pole electromagnet 14 a; d2, a second interval is formed between the middle-end position four-pole electromagnet 14b and the rear-end position four-pole electromagnet 14 c; d3, a third interval between the (front end position) octopole electromagnet 14d and the rear end position quadrupole electromagnet 14 c; d4, a fourth distance between the (front end position) octopole electromagnet 14d and the target 12; d5, the interval between the rear end position octopole electromagnet 14e and the target 12 is the fifth distance.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment described below is only one mode for embodying the present invention, and does not represent that the technical scope of the present invention is limited to the embodiment described below.

Referring to fig. 1, a low-energy charged particlebeam transport system 1 related to BNCT of the present invention is composed of anaccelerator 10, abeam transport line 11, atarget 12, anenergy reduction system 13, a focusinglens 14, and acontrol device 15.

Theaccelerator 10 generates a charged particle beam C, accelerates the generated charged particle beam C by a predetermined electrostatic field, and emits the accelerated charged particle beam C. Theaccelerator 10 is responsible for adjusting the electrostatic field and emitting the charged particle beam C generated by it with a low energy below 5 MeV.

Thebeam transport line 11 transports the charged particle beam C emitted from theaccelerator 10 to apredetermined target 12. Thebeam transport line 11 is constituted by a path connecting the charged particle beam between theaccelerator 10 and thetarget 12.

Thetarget 12 contains lithium (Li), and generates a neutron beam N by being irradiated with the charged particle beam C transported by thebeam transport line 11. The resulting neutron beam N is used for BNCT treatment.

Thetarget 12 is made of lithium and is arranged at the end of the conduit of thebeam transport line 11, and the cross-sectional area of the lithium is smaller than that of the conduit of thebeam transport line 11. Here, depending on the emission direction of the charged particle beam C from theaccelerator 10 to thetarget 12, the side close to theaccelerator 10 is referred to as the front end, and the side close to thetarget 12 is referred to as the rear end.

Theenergy reducing system 13 reduces the energy of the neutron beam N generated by thetarget 12 to the thermal neutron range. A truncated cone of magnesium fluoride having a diameter that increases in the direction of emission of the charged particle beam C is provided at the rear end position of thelithium target 12. Cadmium is arranged at the rear end of the magnesium fluoride, and graphite is arranged around the magnesium fluoride and the cadmium as a reflecting material. High-density polyethylene is arranged around the graphite as a shielding material. At the same time, at the rear end position of cadmium, an opening of a truncated cone with a reduced diameter is provided as a collimator in the emission direction of the charged particle beam C, and the neutron beam N emitted from thelithium target 12 is appropriately condensed and irradiated to the patient. The above elements together constitute theenergy reduction system 13.

The focusinglens 14 is composed of a quadrupole electromagnet and an octopole electromagnet provided inside thebeam transport line 11. Wherein a predetermined number of quadrupole electromagnets are provided along the irradiation direction of the charged particle beam C from a front end position of the charged particle beam C; a predetermined number of octupole electromagnets are provided along the irradiation direction of the charged particle beam C from the front end position of the charged particle beam C. The quadrupole electromagnet and the octopole electromagnet are distributed in thebeam transport line 11 in a direction perpendicular to the emission direction of the charged particle beam C, and the radial profile of the charged particle beam C is controlled by applying a magnetic field to the radial direction of the charged particle beam C. The number of the predetermined number is at least 1.

Thecontrol device 15 controls the magnetic fields of the quadrupole electromagnet and the octopole electromagnet that constitute the focusinglens 13. Thecontrol device 15 is internally provided with a CPU, a ROM, a RAM, an HDD, an SSD, and the like (not shown in fig. 1), and the CPU can operate using the RAM, for example, and execute a program stored in the ROM, the HDD, the SSD, and the like. Moreover, the implementation of each part described later is also realized by the cpu running program.

The configuration and actual flow of the embodiment of the present invention will be described below with reference to fig. 1 and 2. First, the technician starts the low energy charged particlebeam transport system 1 for BNCT, opens the start switch of theaccelerator 10, starts the operation of theaccelerator 10, and then starts the charged particlebeam transport system 1. In the BNCT, thebeam focusing lens 14 of thebeam transport line 11 is controlled in accordance with the operation of theaccelerator 10. In the embodiment of the present invention, the charged particle beam C is a proton beam and is emitted from theaccelerator 10 to thebeam transport line 11.

The present invention contemplates a miniature BNCT utilizing the second of the foregoing⁷ Li（p，n）⁷ Be nuclear reaction. Therefore, the charged particle beam C generated by theaccelerator 10 has a low energy of 5MeV or lessThe amount, for example, is assumed to be in the range of 2MeV to 5 MeV. Further, the current value of theaccelerator 10 is preferably kept within a range of 5mA to 20 mA. Accordingly, a sufficient number of neutrons can be generated for BNCT.

Here, assuming that the energy of the charged particle beam C generated by theaccelerator 10 is 5MeV and the current value of theaccelerator 10 is 10mA, the amount of heat of the charged particle beam C is 10mA × 5mev=50kw. The amount of heat of the charged particle beam C depends on the energy and current value of the charged particle beam C generated by the accelerator. However, although the amount of heat of the charged particle beam C depends on the energy of the charged particle beam C generated by theaccelerator 10, it is preferable to keep the amount in the range of 5kW to 100kW, and most preferable to keep the amount in the range of 10kW to 50kW, in view of the treatment of BNCT. Therefore, the energy reducing system for reducing the energy of the neutron beam N to the thermal neutron range can be manufactured easily and has high feasibility.

Next, the focusinglens control section 102 of thecontrol device 15 controls the magnetic fields of the quadrupole electromagnet and the octopole electromagnet of the focusinglens 14, so that the radial beam profile (cross-sectional shape) of the charged particle beam C is enlarged and the distribution is uniform (fig. 2.

Here, the four-pole electromagnet and the eight-pole electromagnet are configured such that the magnetic poles (S-pole or N-pole) of the plurality of electromagnets are arranged toward the center along the periphery of the charged particle beam C and the magnetic poles thereof are inverted with respect to each other, as shown in fig. 3 and 4. For example, the quadrupole electromagnet is constructed such that the magnetic poles of four electromagnets are arranged toward the center along the periphery of the charged particle beam C and the magnetic poles thereof can be inverted with each other. The eight-pole electromagnet is constructed such that the poles of the eight electromagnets are arranged toward the center along the periphery of the charged particle beam C and the poles thereof can be inverted with respect to each other. The electromagnets constituting the quadrupole electromagnet and the octopole electromagnet are disposed at equal intervals along the periphery of the charged particle beam C toward the center.

In adjusting the radial beam profile (beam profile) of the charged particle beam C, the setting of the number and size of the quadrupole electromagnet and the octapole electromagnet, the setting distance between the quadrupole electromagnet and the octapole electromagnet, the strength of each magnetic field, and other parameters are important. In the embodiment of the present invention, the beam profile (beam profile) is appropriately enlarged and the distribution of the charged particle beam C is made uniform by adjusting the above parameters to an optimum state.

Specifically, when it is desired to enlarge the radial beam profile of the charged particle beam C to a rectangular shape (for example, a square shape), the basic structure of the focusinglens 14 in thebeam transport line 11 is, as shown in fig. 5, a first basic structure in which 3quadrupole electromagnets 14a, 14b, 14C and 1octupole electromagnet 14d are sequentially arranged in this order along the emission direction of the charged particle beam C. In the case where a rectangular beam profile is desired, the configuration of the focusinglens 14 in the present invention requires a minimum of 3quadrupole electromagnets 14a, 14b, 14c and oneoctopole electromagnet 14d. Rectangular includes square, rectangular, and the like.

Here, the length x1 of the front-endposition quadrupole electromagnet 14a (the length in the irradiation direction of the charged particle beam C, i.e., the electromagnet thickness, the same applies hereinafter) and the length x2 of the middle-endposition quadrupole electromagnet 14b, the length x3 of the rear-end position quadrupole electromagnet 14C, and the length x4 of theoctupole electromagnet 14d can be appropriately designed according to the energy of the charged particle beam C emitted from theaccelerator 10 and the current value of theaccelerator 10. The middle-end-position four-pole electromagnet 14b is a four-pole electromagnet provided in the middle between the upper-end-position four-pole electromagnet 14a and the lower-end-position four-pole electromagnet 14 c. The longer the length X1 of thequadrupole electromagnet 14a is, the stronger the influence of the magnetic field from thequadrupole electromagnet 14a on the charged particle beam C is.

Here, the length x1 of the front endposition quadrupole electromagnet 14a, the length x2 of the middle endposition quadrupole electromagnet 14b, and the length x3 of the rear end position quadrupoleelectromagnet 14c are set to be equal in length. That is, the lengths of the 3quadrupole electromagnets 14a, 14b, 14C in the irradiation direction of the charged particle beam C are the same. Accordingly, the magnetic fields of the 3quadrupole electromagnets 14a, 14b, 14C can be uniformly applied to the charged particle beam C. The length x4 of the front endposition octopole electromagnet 14d can be kept equal to the length x1 of the front endposition quadrupole electromagnet 14 a; the lengths of thequadrupole electromagnets 14a, 14b, 14c and theoctupole electromagnet 14d may all be set to be the same length.

In the present invention, since the energy of the charged particle beam C is assumed to be low, i.e., 5MeV, relativelysmall quadrupole electromagnets 14a, 14b, 14C andoctopole electromagnet 14d can be used. The length x1 of the front endposition quadrupole electromagnet 14a, the length x2 of the middle endposition quadrupole electromagnet 14b, and the length x3 of the rear end position quadrupoleelectromagnet 14c may be set within a range of 10cm to 40cm, and the length x4 of theoctopole electromagnet 14d may be set within a range of 10cm to 40 cm.

The middle-end position four-pole electromagnet 14b is spaced from the front-end position four-pole electromagnet 14a by a first distance d1, and is spaced from the rear-end position four-pole electromagnet 14c by a second distance d2. Theoctupole electromagnet 14d is spaced from the rear end position four-pole electromagnet 14c by a third distance d3, and is spaced from thetarget 12 by a fourth distance d4.

Here, the first pitch d1 and the second pitch d2 may be set in a range of 10cm to 40cm, and it is desirable that the first pitch d1 and the second pitch d2 are equal in length. That is, it is desirable that 3quadrupole electromagnets 14a, 14b, 14c are disposed at equal distances from each other. Accordingly, the magnetic fields of the 3quadrupole electromagnets 14a, 14b, 14C can be uniformly applied to the charged particle beam C.

The third distance d3 may be set in the range of 15cm to 100cm, and is preferably set in the range of 1.5 times to 2.5 times thefirst distance d 1. The fourth pitch d4 may be set within a range of 15cm to 100cm, and is preferably equal to the third pitch d 3. The basic distance T from theaccelerator 10 to thetarget 12, that is, the total length of the length x1 and the first pitch d1 of the front-end position four-pole electromagnet 14a, the length x2 and the second pitch d2 of the middle-end position four-pole electromagnet 14b, the length x3 and the third pitch d3 of the rear-end position four-pole electromagnet 14c, and the length x4 and the fourth pitch d4 of theoctapole electromagnet 14d, is set within a range of 90cm to 440 cm.

On the other hand, when it is desired to enlarge the radial beam profile of the charged particle beam C to a circular shape, the basic structure of the focusinglens 14 in thebeam transport line 11 is a second basic structure in which 3quadrupole electromagnets 14a, 14b, 14C and 2octupole electromagnets 14d, 14e are arranged in order in the emission direction of the charged particle beam C, as shown in fig. 6. In the present invention, the focusinglens 14 needs to be composed of at least 3quadrupole electromagnets 14a, 14b, 14c and 2octupole electromagnets 14d, 14e. Circular includes perfect circle, ellipse, etc.

Here, the length x1 of the frontposition quadrupole electromagnet 14a, the length x2 of the middleposition quadrupole electromagnet 14b, the length x3 of the rear position quadrupole electromagnet 14C, the length x4 of the frontposition octopole electromagnet 14d, and the length x5 of the rear position octopoleelectromagnet 14e should be appropriately designed according to the energy of the charged particle beam C generated by theaccelerator 10 and the accelerator current value.

For example, the length x1 of the front endposition quadrupole electromagnet 14a, the length x2 of the middle endposition quadrupole electromagnet 14b, and the length x3 of the rear end position quadrupole electromagnet 14C in the emission direction of the charged particle beam C may be set to be equal. Further, the length x4 of the leading-endposition octupole electromagnet 14d provided behind the trailing-end position quadrupoleelectromagnet 14c and the length x5 of the trailing-end position octupoleelectromagnet 14e may be set to be equal in length. That is, the lengths of the 2octupole electromagnets 14d, 14e in the charged particle beam irradiation direction are equal. Accordingly, the magnetic fields of the 3quadrupole electromagnets 14a, 14b, 14C and the 2octupole electromagnets 14d, 14e can be uniformly applied to the charged particle beam C.

The length x4 of theoctopole electromagnet 14d at the leading end position may be equal to the length x1 of thequadrupole electromagnet 14a at the leading end position, that is, all of thequadrupole electromagnets 14a, 14b, 14c and theoctopole electromagnets 14d, 14e may be equal to each other. Accordingly, the magnetic fields of the 3quadrupole electromagnets 14a, 14b, 14C and the 2octupole electromagnets 14d, 14e can be applied to the charged particle beam C in an extremely uniform manner, so that the charged particle beam C can be amplified to a perfect circle while ensuring uniform distribution.

As described above, in the present invention, relatively small four-pole electromagnets 14a, 14b, and 14c and eight-pole electromagnets 14d and 14e can be used. The length x1 of the front endposition quadrupole electromagnet 14a, the length x2 of the middle endposition quadrupole electromagnet 14b, and the length x3 of the rear end position quadrupoleelectromagnet 14c can be set within the range of 10cm to 40 cm. The length x4 of the leading endposition octupole electromagnet 14d and the length x5 of the trailing end position octupoleelectromagnet 14e may be set within a range of 10cm to 40 cm.

The interval between the middle-endposition quadrupole electromagnet 14b and the front-endposition quadrupole electromagnet 14a is a first interval d1, and the interval between the middle-endposition quadrupole electromagnet 14b and the rear-end position quadrupoleelectromagnet 14c is a second interval d2. The front endposition octupole electromagnet 14d is spaced from the rear end position quadrupoleelectromagnet 14c by a third distance d3, and the rear end position octupoleelectromagnet 14e is spaced from the rear end position octupoleelectromagnet 14e by a fourth distance d4. The rear end position octopoleelectromagnet 14e is spaced from thetarget 12 by a fifth distance d5.

Here, the first interval d1 and the second interval d2 may be set within a range of 10cm to 40cm, and it is preferable that the first interval d1 and the second interval d2 are set to have the same length. That is, as described above, it is preferable that 3quadrupole electromagnets 14a, 14b, and 14c are provided at equal distances from each other.

The third interval d3 may be set in the range of 15cm to 100cm, and is desirably set in the range of 1.5 times to 2.5 times thefirst interval d 1. The fourth interval d4 may be set within a range of 10cm to 40cm, and is preferably set to be equal to the first interval d1 or shorter than thefirst interval d 1. The fifth interval d5 may be set in the range of 15cm to 100cm, and is preferably set to be equal in length to the third interval d 3. The basic distance T from theaccelerator 10 to thetarget 12, i.e., the total length of the length x1 and the first interval d1 of the front-end position four-pole electromagnet 14a, the length x2 and the second interval d2 of the middle-end position four-pole electromagnet 14b, the length x3 and the third interval d3 of the rear-end position four-pole electromagnet 14c, the length x4 and the fourth interval d4 of the front-end position eight-pole electromagnet 14d, and the length x5 and the fifth interval d5 of the rear-end position eight-pole electromagnet 14e, is set within a range of 110cm to 520 cm.

The focusinglens 14 has 2 kinds of first and second basic structures, and the focusinglens control part 102 controls the magnetic fields of a predetermined number of quadrupole electromagnets and a predetermined number of octupole electromagnets, respectively, so that the charged particle beam C is uniformly enlarged in the radial direction by the magnetic fields of the predetermined number of quadrupole electromagnets and the predetermined number of octupole electromagnets.

Here, since the energy of the charged particle beam C and the current value of theaccelerator 10 are kept within the predetermined numerical ranges as described above, the heat quantity of the charged particle beam C can be calculated. Here, the magnetic fields of the predetermined number of quadrupole electromagnets and the predetermined number of octupole electromagnets can be adjusted according to the heat of the charged particle beam C. Accordingly, the collectinglens control section 102 can control the magnetic fields of the predetermined number of quadrupole electromagnets and the predetermined number of octupole electromagnets based on the energy of the charged particle beam C generated by theaccelerator 10 and the current value of theaccelerator 10, respectively.

Here, the magnetic fields of the 3quadrupole electromagnets 14a, 14b, 14c and the 1octopole electromagnet 14d in the first basic configuration may be set as appropriate, respectively.

For example, it is preferable that the magnetic field of the front endposition quadrupole electromagnet 14a is positive, the magnetic field of the middle endposition quadrupole electromagnet 14b is negative, and the magnetic field of the rear end position quadrupoleelectromagnet 14c is positive. Accordingly, the charged particle beam C of the 3quadrupole electromagnets 14a, 14b, and 14C is subjected to the positive, negative, and positive magnetic fields in this order, and the radial beam profile of the charged particle beam C can be uniformly amplified.

Here, it is preferable that the magnetic field of the front-endposition quadrupole electromagnet 14a is set to 5m^-2 —20m^-2 In the range, the magnetic field of the middle-end-position quadrupole electromagnet 14b is set at-5 m^-2 — -20m^-2 Within the range, the magnetic field of the rear end position quadrupoleelectromagnet 14c is set at 5m^-2 —20m^-2 Within the range. It is preferable that the magnetic fields of the front endposition quadrupole electromagnet 14a and the rear end position quadrupoleelectromagnet 14c have the same intensity, and the absolute value of the magnetic field of the front endposition quadrupole electromagnet 14a (or the rear endposition quadrupole electromagnet 14 c) is the same as the absolute value of the magnetic field of the middle endposition quadrupole electromagnet 14 b. Accordingly, a balanced and uniform magnetic field can be applied to the charged particle beam C passing through the 3quadrupole electromagnets 14a, 14b, 14C.

Further, it is preferable that the magnetic field of theoctupole electromagnet 14d is set to the positive direction. Accordingly, the charged particle beam C of theoctopole electromagnet 14d receives the forward magnetic field, and the radial beam profile of the charged particle beam C can be uniformly enlarged to a rectangular shape.

Here, it is desirable that the magnetic field of theoctapole electromagnet 14d be set to 1000m^-4 —5000m^-4 Within the range of 1000m^-2 —4000m^-2 More ideal in range.

In addition, the magnetic fields of the 3quadrupole electromagnets 14a, 14b, 14c and the 2octupole electromagnets 14d, 14e in the second basic configuration may be set in the same manner as described above.

For example, as described above, it is preferable that the magnetic field of the front endposition quadrupole electromagnet 14a is set to the positive direction, the middle endposition quadrupole electromagnet 14b is set to the negative direction, and the rear end position quadrupoleelectromagnet 14c is set to the positive direction.

Here, it is preferable that the magnetic field of the front-endposition quadrupole electromagnet 14a is set to 5m^-2 —20m^-2 Within the range; the magnetic field of the middle-end-position quadrupole electromagnet 14b is set to-5 m^-2 —

-20m^-2 Within the range; the magnetic field of the rear end position quadrupoleelectromagnet 14c is set to 5m^-2 —20m^-2 Within the range. It is preferable that the magnetic fields of the front endposition quadrupole electromagnet 14a and the rear end position quadrupoleelectromagnet 14c have the same intensity, and the absolute value of the magnetic field of the front endposition quadrupole electromagnet 14a (or the rear endposition quadrupole electromagnet 14 c) is the same as the absolute value of the magnetic field of the middle endposition quadrupole electromagnet 14 b. It is preferable that the absolute value of the magnetic field of the front-endposition quadrupole electromagnet 14a be an intermediate value, a value obtained by adding the intermediate value to a predetermined value be an upper limit value, and a value obtained by subtracting the intermediate value from the predetermined value be a lower limit value. Accordingly, a balanced and uniform magnetic field can be applied to the charged particle beam C passing through the 3quadrupole electromagnets 14a, 14b, 14C.

In addition, it is considered that the configuration of the 3quadrupole electromagnets 14a, 14b, and 14C in both the first basic configuration and the second basic configuration contributes to uniform and uniform amplification of the radial beam profile of the charged particle beam C.

It is preferable that the magnetic field of the leading-endposition octupole electromagnet 14d is positive, and the magnetic field of the trailing-end position octupoleelectromagnet 14e is negative. Accordingly, the charged particle beam C of the 2octupole electromagnets 14d, 14e is sequentially subjected to the positive and negative magnetic fields, and the radial beam profile of the charged particle beam C can be uniformly and uniformly enlarged to a circular shape.

Here, it is most preferable to position the leading end position of the octupole electromagnet14d magnetic field set at 1000m^-4 —4000m^-4 Within the range; the magnetic field of the rear end position eight-pole electromagnet 14e is set to

-1000m^-2 — -4000m^-2 Within the range. It is preferable that the absolute value of the magnetic field of the rear-end position octupoleelectromagnet 14e is the same as the absolute value of the magnetic field of the front-endposition octupole electromagnet 14d. It is preferable that the absolute value of the magnetic field of the leading-endposition octopole electromagnet 14d is set as an intermediate value, a value obtained by adding the intermediate value to a predetermined value is set as an upper limit value, and a value obtained by subtracting the intermediate value from the predetermined value is set as a lower limit value. Accordingly, a balanced and uniform magnetic field can be applied to the charged particle beam C passing through the 2octopole electromagnets 14d, 14e.

The charged particle beam C amplified to a certain range and uniformly distributed irradiates the lithium of thetarget 12 through thebeam transport line 11 to generate⁷ Li（p，n）⁷ Be nuclear reaction, producing neutron beam N. The generated neutron beam N is reduced to the thermal neutron range by the rear end positionenergy reducing system 13, and becomes the thermal neutron necessary for BNCT treatment. The neutron beam N irradiates a patient positioned at the rear end of theenergy reduction system 13.

Here, the patient is injected with a boron compound which selectively accumulates in the cancer cells, and the cancer cells containing the boron compound are irradiated with neutron beam N, which occurs¹⁰ B（n，α）⁷ The Li nuclei react, producing alpha particles with the lithium nuclei and destroying the cancer cells. The above is the BNCT treatment principle.

Here, since the beam profile (beam profile) in the radial direction of the charged particle beam C is wide and uniformly distributed, lithium in thetarget 12 is not evaporated, and a suitable amount of the neutron beam N can be generated.

In the embodiment of the present invention, the basic configuration of the focusinglens 14 is composed of 2 kinds of focusinglenses 14, but the present invention may be applied to other configurations including the above-described basic configuration. For example, as shown in fig. 7 and 8, in the case where the overall distance T0 from theaccelerator 10 to thetarget 12 is longer than the basic distance T consisting of 3quadrupole electromagnets 14a, 14b, 14C andoctupole electromagnet 14d, 1 ormore quadrupole electromagnets 14e, 14f may be additionally provided between theaccelerator 10 and thequadrupole electromagnet 14a located at the front end position of the focusinglens 14, in order to prevent the charged particle beam C emitted from theaccelerator 10 and passing through thequadrupole electromagnet 14a at the front end position from diverging. The basic distance T, e.g., a distance corresponding to one room, and the total distance T0, e.g., a distance corresponding to two or more rooms, are from theaccelerator 10 to thebeam transport line 11 and through thetarget 12 to the treatment room, which corresponds to a distance spanning two or more rooms. The four-pole electromagnets 14e and 14f are disposed at a predetermined distance from theaccelerator 10 to the front end position four-pole electromagnet 14 a.

Here, the structure of theadditional quadrupole electromagnets 14e and 14f is not particularly required, and the design thereof can be added as needed depending on the energy of the charged particle beam C emitted from theaccelerator 10, the current value of theaccelerator 10, and the difference between the overall distance T0 and the basic distance T. For example, the length of the four-pole electromagnets 14e and 14f added is set to be equal to the length x1 of the front end position four-pole electromagnet 14 a; according to the difference between the overall distance T0 and the basic distance T, 1 can be additionally arranged according to actual needs or a plurality of distances can be arranged according to specified intervals.

Similarly, in the case where the basic structure is 3quadrupole electromagnets 14a, 14b, 14c and 2octupole electromagnets 14d, 14e, 1 ormore quadrupole electromagnets 14f, 14g can be added as appropriate between theacceleration device 10 and thequadrupole electromagnet 14a at the front end position of the beam-collectinglens 14, as shown in fig. 9 and 10.

In the second type of focusinglens 14, 1 octupole electromagnet may be added from the octupole electromagnet at the rear end position to thetarget 12 to adjust the radial beam profile of the charged particle beam C.

Examples

Hereinafter, examples of the present invention and comparative examples will be specifically described, but the application of the present invention is not limited to the examples and the like below.

The beam profile calculation code crystlal used innon-patent document 1 is used for the design of the focusinglens 14 in thebeam transport line 11 and the beam profile (beam profile) in the radial direction of the charged particle beam C. The configuration of thecondenser lens 14 is determined by designing thecondenser lens 14 using the beam streamline calculation code CRYSTAL and confirming the simulation result of the charged particle beam C radial beam profile (beam profile).

First, the focusinglens 14 in thebeam transport line 11 is configured by a plurality of quadrupole electromagnets and a plurality of octopole electromagnets.

Next, the charged particle beam C irradiated to the front endposition quadrupole electromagnet 14a is set. Among the parameters indicating the spatial spread and the advancing angle of the charged particle beam C, α and β are set to predetermined values, respectively. The parameter values correspond to the low energy protons used in BNCT.

A beam profile (beam profile) in the radial direction of the charged particle beam C after passing through the predetermined charged particle beam C is simulated by passing the charged particle beam C through the focusinglens 14 having the above-described structure. Here, the beam profile (beam profile) in the radial direction of the charged particle beam C has a profile transverse direction of the x axis and a profile longitudinal direction of the y axis, and the origin is the center position of the charged particle beam C.

In the simulation calculation, by adjusting each parameter and measuring the radial beam profile of the charged particle beam C after passing through the magnetic field, it is found that the measurement data all show that the beam profile is uniformly and consistently amplified. The parameters refer to the number and the size of the four-pole electromagnet and the eight-pole electromagnet, the setting interval among the electromagnets, the strength of a magnetic field and the like.

As a result of the simulation calculation, as shown in fig. 11 to 16, in the initial beam profile (beam profile), many charged particles are concentrated near the origin, and the number of charged particles is distributed in an approximate mountain shape regardless of the x-axis beam profile (beam profile) or the y-axis beam profile (beam profile). That is, the charged particle distribution in the beam profile (beam profile) in the radial direction of the charged particle beam C emitted from theaccelerator 10 increases as the number of bands approaches the center position. When lithium of thetarget 12 is irradiated with the charged particle beam C in this state, heat is concentrated near the center of lithium, and evaporation of lithium may occur.

Under certain conditions of simulation calculation (α =0.1, β = 39), the focusinglens 14 in thebeam transport line 11 is as shown in the figureShown in fig. 5, is composed of 3quadrupole electromagnets 14a, 14b, 14c, and 1octupole electromagnet 14d. At this time, the length x1 of the four-pole electromagnet 14a at the front end position, the length x2 of the four-pole electromagnet 14b at the middle end position, the length x3 of the four-pole electromagnet 14c at the rear end position, and the length x4 of the eight-pole electromagnet 14d are set to 20cm, respectively. Further, the lengths of the first interval d1 and the second interval d2 are made 25cm, respectively, and the third interval d3 and the fourth interval d4 are made 50cm, respectively. In this case, the basic distance T is 230cm. Further, the magnetic field of the front-endposition quadrupole electromagnet 14a is set to 13.0m^-2 The magnetic field of thequadrupole electromagnet 14b at the middle position is-13.0 m^-2 The magnetic field of the rear-end position quadrupoleelectromagnet 14c is 13.0m^-2 The magnetic field of the eight-pole electromagnet 14d is 3000m^-4 。

As a result of the above simulation, as shown in fig. 11 to 16, in the beam profile (beam profile) after passing through the cluster lens, the charged particles are uniformly enlarged from the vicinity of the origin to the four sides in a rectangular shape (nearly square shape). More surprisingly, the number of charged particles on either the x-axis beam profile (beam profile) or the y-axis beam profile (beam profile) is substantially uniformly distributed except for both ends. This indicates that the charged particle beam C has been correctly enlarged to a wide area and is uniformly distributed. When the charged particle beam C in this state is used to irradiate lithium of thetarget 12, heat is not concentrated near the center of lithium, and evaporation of lithium can be prevented.

Further simulation calculation results show that, under other simulation calculation conditions (α = -0.1, β = 31), the focusinglens 14 in thebeam transport line 11 is configured by 3quadrupole electromagnets 14a, 14b, 14c and 2octupole electromagnets 14d, 14e as shown in fig. 6. At this time, the length x1 of the four-pole electromagnet 14a at the front end position, the length x2 of the four-pole electromagnet 14b at the middle end position, the length x3 of the four-pole electromagnet 14c at the rear end position, and the length x4 of the eight-pole electromagnet 14d are set to 20cm, respectively. The first interval d1 and the second interval d2 are set to be 25cm, the third interval d3 is set to be 50cm, the fourth interval d4 is set to be 20cm, and the fifth interval d5 is set to be 50cm, respectively. In this case, the basic distance T is 270cm. Further, the magnetic field of the front endposition quadrupole electromagnet 14a is set to 12.1m^-2 Magnetism of middle-end position four-pole electromagnet 14bField is-13.1 m^-2 The magnetic field of the rear end position quadrupoleelectromagnet 14c is 12.1m^-2 The magnetic field of the front position eight-pole electromagnet 14d is 2000m^-4 The magnetic field of the rear end position eight-pole electromagnet 14e is-3000 m^-4 。

As a result of the above simulation calculation, as shown in fig. 17 to 22, in the beam profile (beam profile) after passing through the beam focusing lens, the charged particles are uniformly enlarged in a circular shape from the vicinity of the origin to the four surfaces. More surprisingly, the charged particle amount on either the x-axis beam profile (beam profile) or the y-axis beam profile (beam profile) is substantially uniformly distributed. This indicates that the charged particle beam C has been correctly enlarged to a wide area and is uniformly distributed. When the charged particle beam C in this state is used to irradiate lithium of thetarget 12, heat is not concentrated in the vicinity of the center of the lithium target, and evaporation of lithium can be prevented.

It can be considered that the portion contributing to the uniform and uniform expansion of the charged particle beam C is 3 quadrupole electromagnets; the portion that contributes to the shape of the charged particle beam C is the number of octapole electromagnets.

As described above, according to the present invention, it is possible to uniformly transport a charged particle beam of low energy and large current in a wide range in association with BNCT. In the invention, the introduction of BNCT equipment into hospitals can be promoted by the miniaturization of the accelerator for BNCT and the optimization of thebeam transport line 11cluster lens 14 matched with the accelerator.

In summary, the low-energy charged particle beam transport system and the charged particle beam transport method related to BNCT in the present invention are advantageous for implementing high-precision treatment by BNCT, and the low-energy large-current charged particle beam related to BNCT can be uniformly and uniformly transported in a wide range, and are effective as the low-energy charged particle beam transport system and the charged particle beam transport method related to BNCT.

Claims (4)

1. A BNCT-related low energy charged particle beam transport system, comprising: the method comprises the following steps: an accelerator for emitting a low-energy charged particle beam of 5MeV or less,

A beam transport line for transporting the charged particle beam emitted by the accelerator,

A target containing lithium and generating a neutron beam by irradiation of the charged particle beam transported by the beam transport line,

An energy reducing system for reducing the energy of the neutron beam generated by the target to a thermal neutron range,

A focusing lens located inside the beam transport line and composed of a predetermined number of quadrupole electromagnets arranged along the charged particle beam irradiation direction from the upper end of the charged particle beam and a predetermined number of octupole electromagnets arranged along the charged particle beam irradiation direction from the rear end position quadrupole electromagnet,

By controlling the magnetism of the quadrupole electromagnet and the octopole electromagnet, the radial beam profile of the charged particle beam is amplified, and a uniform and consistent control part of the focusing lens is realized.

2. A BNCT-related low energy charged particle beam transport system according to claim 1, wherein: the number of the four-pole electromagnets is 3, and among the 3 four-pole electromagnets, the magnetic field of the front end position four-pole electromagnet is set to be positive, the magnetic field of the middle end position four-pole electromagnet is set to be negative, and the magnetic field of the rear end position four-pole electromagnet is set to be positive.

3. A BNCT-related low energy charged particle beam transport system according to claim 1, wherein: the number of the eight-pole electromagnets is 1 or 2.

4. A BNCT-related method for low-energy charged particle beam transport, comprising: the method comprises the following steps: the accelerator emits low-energy charged particle beams below 5MeV,

The beam transport line transports the charged particle beam emitted by the accelerator,

A target containing lithium, a neutron beam generated by irradiation of the charged particle beam transported by the beam transport line,

The energy reducing system reduces the energy of the neutron beam generated by the target to a thermal neutron range,

A beam condensing lens located inside the beam transport line and including a predetermined number of quadrupole electromagnets arranged along the charged particle beam irradiation direction from the upper end of the charged particle beam and a predetermined number of octapole electromagnets arranged along the charged particle beam irradiation direction from the rear end position quadrupole electromagnet; the bundling lens control part amplifies the radial beam profile of the charged particle beam by controlling the magnetism of the quadrupole electromagnet and the octopole electromagnet, and realizes uniformity.

Images