CN111821581A

CN111821581A - Neutron capture therapy system and beam shaper for neutron capture therapy system

Info

Publication number: CN111821581A
Application number: CN201910308298.5A
Authority: CN
Inventors: 陈韦霖; 江涛
Original assignee: China Boron Xiamen Medical Equipment Co ltd
Current assignee: China Boron Xiamen Medical Equipment Co ltd
Priority date: 2019-04-17
Filing date: 2019-04-17
Publication date: 2020-10-27

Abstract

A neutron capture treatment system and a beam shaper for the neutron capture treatment system can prevent the beam shaper material from deforming and damaging and improve the flux and the quality of a neutron source. The neutron capture treatment system comprises a neutron generating device and a beam shaping body, wherein the neutron generating device comprises an accelerator and a target material, charged particle rays generated by acceleration of the accelerator act on the target material to generate neutrons, the neutrons form a neutron beam, the neutron beam defines a main shaft, the beam shaping body comprises a supporting part for supporting the beam shaping body, the supporting part comprises a wall surrounding the main shaft, and the basic part and the supplementary part are made of different materials and are separated by the wall.

Description

Neutron capture therapy system and beam shaper for neutron capture therapy system

Technical Field

The invention relates to a radiation irradiation system, in particular to a neutron capture treatment system; another aspect of the invention relates to a beam shaper for a radiation exposure system, in particular for a neutron capture therapy system.

Background

With the development of atomic science, radiation therapy such as cobalt sixty, linacs, electron beams, etc. has become one of the main means of cancer treatment. However, the traditional photon or electron therapy is limited by the physical conditions of the radiation, and can kill tumor cells and damage a large amount of normal tissues in the beam path; in addition, due to the difference of the sensitivity of tumor cells to radiation, the conventional radiotherapy has poor effect on the treatment of malignant tumors with relatively high radiation resistance, such as multiple linear glioblastoma (glioblastomas) and melanoma (melanomas).

In order to reduce the radiation damage of normal tissues around tumor, the target therapy concept in chemotherapy (chemotherapy) is applied to radiotherapy; for tumor cells with high radiation resistance, radiation sources with high Relative Biological Effect (RBE) are also actively developed, such as proton therapy, heavy particle therapy, neutron capture therapy, etc. Wherein, the neutron capture treatment combines the two concepts, such as boron neutron capture treatment, and provides better cancer treatment selection than the traditional radioactive rays by the specific accumulation of boron-containing drugs in tumor cells and the precise neutron beam regulation.

Boron Neutron Capture Therapy (BNCT) utilizes Boron-containing (B: (B-N-C-B-N-C-¹⁰B) The medicine has the characteristic of high capture cross section for thermal neutrons¹⁰B(n,α)⁷Li neutron capture and nuclear fission reaction generation⁴He and⁷li two heavily charged particles. Referring to FIGS. 1 and 2, schematic and graphical illustrations of boron neutron capture reactions are shown, respectively¹⁰B(n,α)⁷The Li neutron capture nuclear reaction equation has the average energy of two charged particles of about 2.33MeV, has high Linear Energy Transfer (LET) and short-range characteristics, and the Linear energy transfer and range of alpha particles are 150 keV/mum and 8μm respectively⁷The Li heavily-charged particles are 175 keV/mum and 5μm, the total range of the two particles is about equal to the size of a cell, so the radiation damage to organisms can be limited at the cell level, when boron-containing drugs selectively gather in tumor cells, and a proper neutron source is matched, the aim of locally killing the tumor cells can be achieved on the premise of not causing too much damage to normal tissues.

The effect of boron neutron capture therapy is also called binary cancer therapy (binary cancer therapy) because the effect depends on the boron-containing drug concentration and the quantity of thermal neutrons at the tumor cell position; it is known that, in addition to the development of boron-containing drugs, the improvement of neutron source flux and quality plays an important role in the research of boron neutron capture therapy.

Therefore, a new technical solution is needed to solve the above problems.

Disclosure of Invention

In order to improve the flux and quality of a neutron source, one aspect of the invention provides a beam shaper for a neutron capture therapy system, the neutron capture therapy system comprising a neutron generating device, the neutron generating device comprising an accelerator and a target, a charged particle beam generated by acceleration of the accelerator interacting with the target to generate neutrons, the neutrons forming a neutron beam, the neutron beam defining a principal axis, the beam shaper comprising a moderator decelerating neutrons generated by the neutron generating device to a epithermal neutron energy region, a reflector surrounding the moderator and directing neutrons deviating from the principal axis back to the principal axis to increase the epithermal neutron beam intensity, and a radiation shield for shielding leaked neutrons and photons to reduce the normal tissue dose in non-irradiated regions, the retarder comprises a base portion and a supplementary portion surrounding the base portion, the beam shaper further comprising a support for supporting the beam shaper, the support comprising a wall surrounding the main axis, the base portion and the supplementary portion being of different materials and being spaced apart by the wall. The supporting part can prevent the main body material of the beam shaping body from deforming and damaging, and the target changing and the beam quality are influenced; the supplementary part is made of materials which are easy to obtain, so that the manufacturing cost of the retarder can be reduced, a certain neutron retarding effect is achieved, and the beam quality is not greatly influenced.

Preferably, the walls include a first wall, a second wall and a transverse plate, the first wall, the second wall and the transverse plate are sequentially arranged along the neutron beam direction and circumferentially enclosed around the neutron beam direction, the transverse plate extends perpendicular to the neutron beam direction, the first wall is used for installing a transmission tube of the accelerator, and the second wall forms a containing cavity of a basic part of the retarder; the material of the basic part comprises D₂O、Al、AlF₃、MgF₂、CaF₂、LiF、Li₂CO₃Or Al₂O₃At least one of the two has a large fast neutron action section and a small epithermal neutron action section, and has a good retarding effect; the basic part contains Li-6, said substantial portion simultaneously acting as said thermal neutron absorber.

Further, the basic portion comprises a first end face and a second end face which are basically vertical to the neutron beam direction, the first end face and the second end face are sequentially arranged along the neutron beam direction, a central hole is formed in the first end face and used for accommodating the transmission tube and the target, the radial distance from the first wall to the main shaft is smaller than the radial distance from the second wall to the main shaft, and the basic portion of the retarder surrounds the target, so that neutrons generated by the target can be effectively slowed down in all directions, and the neutron flux and the beam quality can be further improved. And a shielding plate is arranged adjacent to the second end face, the shielding plate is a lead plate, lead can absorb gamma rays released from the retarder, and the thickness of the shielding plate in the neutron beam direction is less than or equal to 5cm, so that neutrons passing through the retarder cannot be reflected.

As another preference, the support further comprises a radial partition dividing the complementary part in a circumferential direction around the main shaft into at least two sub-modules, the plane of which extends through the main shaft, the at least two sub-modules being spaced apart by the radial partition.

As another preferred mode, the supplementary portion includes first and second supplementary units adjacent to each other, the basic portion, the first and second supplementary units are made of different materials, the basic portion is columnar, and the first and second supplementary units are integrally formed to include at least one cone-like shape, so that better beam quality and treatment effect can be obtained.

Further, the material of the first supplementary unit comprises at least one of Zn, Mg, Al, Pb, Ti, La, Zr, Bi, Si and C, and the material of the second supplementary unit is Teflon or graphite. The first and second supplementary units are sequentially arranged along the neutron beam direction, and the first and second supplementary units are integrally arranged into two mutually adjacent cone shapes in opposite directions. The first supplement part of the retarder is made of materials which are easy to obtain, so that the manufacturing cost of the retarder can be reduced, and meanwhile, the first supplement part has a certain neutron retarding effect and cannot greatly influence the beam quality; the second supplementary part is made of a material with a better fast neutron absorption effect than that of the first supplementary part, so that the fast neutron content in the beam can be reduced.

Further, the first supplementing unit is provided in two cone shapes which are mutually adjacent in opposite directions, the first supplementing unit comprises a first cone portion and a second cone portion which are sequentially arranged along the neutron beam direction, the radial dimension of the outer contour of the first cone portion gradually increases along the overall trend of the neutron beam direction, the second cone portion is connected with the first cone portion at the position where the radial dimension of the outer contour of the first cone portion is maximum, the radial dimension of the outer contour of the second cone portion gradually decreases along the overall trend of the neutron beam direction, the second supplementing unit is adjacent to the second cone portion at the position where the radial dimension of the outer contour of the second cone portion is minimum, and the radial dimension of the outer contour of the second supplementing unit gradually decreases along the overall trend of the neutron beam direction.

Furthermore, the cross-sectional profiles of the first and second supplement units along the plane of the main axis are trapezoids or polygons, the first supplement unit has a first side contacting with the reflector at the first cone part, a second side contacting with the reflector and a third side contacting with the second supplement unit at the second cone part, and a fourth side contacting with the wall at the first and second cone parts, the second supplement unit has a fifth side contacting with the first supplement unit, a sixth side contacting with the reflector and a seventh side contacting with the wall, the third and fifth sides are adjacent and serve as the interface of the first and second supplement units, and the interface is perpendicular to the neutron beam direction.

The neutron capture treatment system and the beam shaper thereof can prevent the material of the beam shaper from deforming and damaging and improve the flux and the quality of a neutron source.

Drawings

FIG. 1 is a schematic diagram of a boron neutron capture reaction;

FIG. 2 is¹⁰B(n,α)⁷A Li neutron capture nuclear reaction equation;

FIG. 3 is a schematic view of a neutron capture therapy system according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a beam shaper of a neutron capture therapy system of an embodiment of the invention;

FIG. 5 is a schematic view of the support portion of FIG. 4;

FIG. 6 is an exploded view of the retarder of FIG. 4;

FIG. 7 is a schematic view of the main frame of FIG. 5 as viewed from the direction of the neutron beam N;

fig. 8 is a schematic view of the main frame of fig. 5 viewed from a direction opposite to the direction of the neutron beam N.

Detailed Description

The present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.

Referring to fig. 3, the neutron capture therapy system in the present embodiment is preferably a boron neutron capture therapy system 100, which includes a neutron generating device 10, a beam shaper 20, a collimator 30, and a treatment table 40. The neutron generating apparatus 10 includes an accelerator 11 and a target T, and the accelerator 11 accelerates charged particles (such as protons, deuterons, etc.) to generate a charged particle beam P such as a proton beam, and the charged particle beam P irradiates the target T and reacts with the target T to generate neutrons, which form a neutron beam N, the neutron beam N defining a main axis X, and the target T is preferably a metal target. The illustrated and described later, the neutron beam N direction does not represent the actual neutron motion direction, but represents the direction of the overall motion trend of the neutron beam N. The appropriate nuclear reactions are selected based on the desired neutron yield and energy, the available energy and current for accelerating charged particles, the physical properties of the metal target, and the like, and the nuclear reactions in question include⁷Li(p,n)⁷Be and⁹Be(p,n)⁹b, both reactions are endothermic. The energy threshold of the two nuclear reactions is 1.881MeV and 2.055MeV respectively, because the ideal neutron source for boron neutron capture treatment is an epithermal neutron with keV energy level, theoretically if a metallic lithium target is bombarded by protons with energy only slightly higher than the threshold, a neutron with relatively low energy can be generated, and the energy threshold is not higher than that of the proton bombardmentIt requires too much slowing treatment for clinical application, however, the two targets of lithium metal (Li) and beryllium metal (Be) have low cross-section with threshold energy protons, and in order to generate a sufficient neutron flux, the high-energy protons are usually selected to initiate nuclear reaction. An ideal target should have the characteristics of high neutron yield, neutron energy distribution generated close to the hyperthermic neutron energy region (described in detail below), not too much intense penetrating radiation generation, safety, cheapness, easy operation, and high temperature resistance, but practically no nuclear reaction meeting all the requirements can be found. As is well known to those skilled in the art, the target T may Be made of a metal material other than Li and Be, for example, Ta or W, an alloy thereof, or the like. The accelerator 11 may be a linear accelerator, a cyclotron, a synchrotron, a synchrocyclotron.

The neutron source for boron neutron capture therapy generates a mixed radiation field, namely a beam contains neutrons with low energy to high energy and photons; for boron neutron capture therapy of deep tumors, the greater the amount of radiation other than epithermal neutrons, the greater the proportion of non-selective dose deposition in normal tissue, and therefore the unnecessary dose of radiation that these would cause should be minimized. In addition to the air beam quality factor, in order to better understand the dose distribution caused by neutrons in the human body, the embodiment of the present invention uses a human head tissue prosthesis to perform dose calculation, and uses the prosthesis beam quality factor as a design reference of the neutron beam, which will be described in detail below.

The International Atomic Energy Agency (IAEA) gives five air beam quality factor suggestions aiming at a neutron source for clinical boron neutron capture treatment, and the five suggestions can be used for comparing the advantages and disadvantages of different neutron sources and serving as reference bases for selecting neutron generation paths and designing beam integrators. The five proposals are as follows:

epithermal neutron beam flux Epithermal neutron flux>1x 10⁹n/cm²s

Fast neutron contamination<2x 10^-13Gy-cm²/n

Photon contamination of Photon contamination<2x 10^-13Gy-cm²/n

Thermal to epithermal neutron flux ratio of thermal to epithermal neutron flux ratio <0.05

Neutron current to flux ratio epithermal neutron current to flux ratio >0.7

Note: the super-thermal neutron energy region is between 0.5eV and 40keV, the thermal neutron energy region is less than 0.5eV, and the fast neutron energy region is greater than 40 keV.

1. Epithermal neutron beam flux:

the neutron beam flux and the boron-containing drug concentration in the tumor together determine the clinical treatment time. If the concentration of the boron-containing drug in the tumor is high enough, the requirement on the neutron beam flux can be reduced; conversely, if the boron-containing drug concentration in the tumor is low, high-throughput epithermal neutrons are required to administer a sufficient dose to the tumor. IAEA requirements for epithermal neutron beam flux are greater than 10 epithermal neutrons per second per square centimeter⁹The neutron beam at this flux can generally control the treatment time within one hour for the current boron-containing drugs, and the short treatment time can effectively utilize the limited residence time of the boron-containing drugs in the tumor besides having advantages on the positioning and comfort of the patient.

2. Fast neutron contamination:

since fast neutrons cause unnecessary normal tissue doses and are therefore considered contamination, the dose magnitude and neutron energy are positively correlated, and the fast neutron content should be minimized in the neutron beam design. Fast neutron contamination is defined as the fast neutron dose accompanied by a unit epithermal neutron flux, and the recommendation for fast neutron contamination by IAEA is less than 2x 10^-13Gy-cm²/n。

3. Photon contamination (gamma ray contamination):

gamma rays belong to intense penetrating radiation and can non-selectively cause the deposition of dose on all tissues on a beam path, so that the reduction of the content of the gamma rays is also a necessary requirement for neutron beam design, the gamma ray pollution is defined as the gamma ray dose accompanied by unit epithermal neutron flux, and the recommendation of IAEA for the gamma ray pollution is less than 2x 10^-13Gy-cm²/n。

4. Thermal neutron to epithermal neutron flux ratio:

because the thermal neutrons have high attenuation speed and poor penetrating power, most energy is deposited on skin tissues after entering a human body, and the thermal neutrons content is reduced aiming at deep tumors such as brain tumors and the like except that the epidermal tumors such as melanoma and the like need to use thermal neutrons as a neutron source for boron neutron capture treatment. The IAEA to thermal neutron to epithermal neutron flux ratio is recommended to be less than 0.05.

5. Neutron current to flux ratio:

the neutron current-to-flux ratio represents the beam directivity, the larger the ratio is, the better the neutron beam directivity is, the neutron beam with high directivity can reduce the dosage of the surrounding normal tissues caused by neutron divergence, and in addition, the treatable depth and the positioning posture elasticity are also improved. The IAEA to neutron current to flux ratio is recommended to be greater than 0.7.

The prosthesis is used to obtain the dose distribution in the tissue, and the quality factor of the prosthesis beam is deduced according to the dose-depth curve of the normal tissue and the tumor. The following three parameters can be used to make comparisons of therapeutic benefits of different neutron beams.

1. Effective treatment depth:

the tumor dose is equal to the depth of the maximum dose of normal tissue, after which the tumor cells receive a dose less than the maximum dose of normal tissue, i.e. the advantage of boron neutron capture is lost. This parameter represents the penetration of the neutron beam, with greater effective treatment depth indicating a greater depth of tumor that can be treated, in cm.

2. Effective treatment depth dose rate:

i.e. the tumor dose rate at the effective treatment depth, is also equal to the maximum dose rate for normal tissue. Because the total dose received by normal tissues is a factor influencing the size of the total dose which can be given to the tumor, the parameter influences the length of the treatment time, and the larger the effective treatment depth dose rate is, the shorter the irradiation time required for giving a certain dose to the tumor is, and the unit is cGy/mA-min.

3. Effective therapeutic dose ratio:

the average dose ratio received from the surface of the brain to the effective treatment depth, tumor and normal tissues, is called the effective treatment dose ratio; the average dose can be calculated by integrating the dose-depth curve. The larger the effective therapeutic dose ratio, the better the therapeutic benefit of the neutron beam.

In order to make the beam shaper design more dependent, in addition to the five IAEA proposed beam quality factors in air and the three parameters mentioned above, the following parameters for evaluating the performance of neutron beam dose are also utilized in the embodiments of the present invention:

1. the irradiation time is less than or equal to 30min (proton current used by an accelerator is 10mA)

2. 30.0RBE-Gy for treating depth greater than or equal to 7cm

3. Maximum tumor dose is more than or equal to 60.0RBE-Gy

4. Maximum dose of normal brain tissue is less than or equal to 12.5RBE-Gy

5. Maximum skin dose not greater than 11.0RBE-Gy

Note: RBE (relative Biological Effect) is a relative Biological effect caused by photons and neutrons

The biological effects are different, so the above dose terms are multiplied by the relative biological effects of different tissues respectively to obtain the equivalent dose.

The neutron beam N generated by the neutron generator 10 is irradiated to the patient 200 on the treatment table 40 through the beam shaper 20 and the collimator 30 in this order. The beam shaper 20 can adjust the beam quality of the neutron beam N generated by the neutron generating device 10, and the collimator 30 is used for converging the neutron beam N, so that the neutron beam N has high targeting performance in the treatment process. The beam shaper 20 further comprises a support 21 (not shown in fig. 1, described in detail below) and a body portion 23 filled in the support 21, the support 21 forming at least one receiving cell C1-C4, each receiving at least a part of the body portion 23. The support part can prevent the main body part material from deforming and damaging, and the target changing and the beam quality are influenced. The main body 23 includes a retarder 231, a reflector 232 and a radiation shield 233, and neutrons generated by the neutron generating apparatus 10 need to be reduced as much as possible in content of neutrons and photons to avoid injury to operators or patients, in addition to epithermal neutrons satisfying treatment needs due to wide energy spectrum, so that neutrons come out of the neutron generating apparatus 10The fast neutron energy of the neutrons needs to be adjusted to the epithermal neutron energy zone through the retarder 231, the retarder 231 is made of a material with a large fast neutron action section and a small epithermal neutron action section, for example, the material includes D₂O、Al、AlF₃、MgF₂、CaF₂、LiF、Li₂CO₃Or Al₂O₃At least one of; the reflector 232 surrounds the retarder 231 and reflects neutrons diffused to the periphery through the retarder 231 back to the neutron beam N to improve utilization rate of the neutrons, and the reflector 232 is made of a material having a strong neutron reflection capability, such as at least one of Pb or Ni; the radiation shield 233 is used to shield the leaked neutrons and photons to reduce the normal tissue dose in the non-irradiated region, and the material of the radiation shield 233 includes at least one of photon shielding material and neutron shielding material, such as photon shielding material lead (Pb) and neutron shielding material Polyethylene (PE). It will be appreciated that the body portion may have other configurations as long as the desired hyperthermal neutron beam for treatment is obtained. The target T is disposed between the accelerator 11 and the beam shaper 20, the accelerator 11 has a transport tube 111 carrying the charged particle beam P, in this embodiment, the transport tube 111 extends into the beam shaper 20 along the charged particle beam P and sequentially passes through the retarder 231 and the reflector 232, and the target T is disposed in the retarder 231 and at the end of the transport tube 111 to obtain better neutron beam quality. In this embodiment, the first and second cooling tubes D1 and D2 are disposed between the transport tube 111 and the retarder 231 and the reflector 232, one end of each of the first and second cooling tubes D1 and D2 is connected to a cooling inlet (not shown) and a cooling outlet (not shown) of the target T, and the other end is connected to an external cooling source (not shown). It will be appreciated that the first and second cooling tubes may be otherwise disposed within the beam shaper and may be eliminated when the target material is disposed outside of the beam shaper.

Referring to fig. 4 and 5, the support portion 21 includes an outer wall 211 circumferentially enclosed around the main axis X, and first and

second side plates

221, 222 respectively disposed on both sides of the outer wall 211 along the direction of the neutron beam N and connected to the outer wall 211, the first side plate 221 is provided with a hole 2211 through which the transmission tube 111 passes, the second side plate 222 is provided with a hole 2221 forming a beam outlet, a receiving portion C is formed between the outer wall 211 and the first and

second side plates

221, 222, and the main body portion 23 is disposed in the receiving portion C. The container C includes at least one container unit C1-C4 (described in detail below), each container unit C1-C4 contains at least 1 of the retarder 231, the reflector 232, and the radiation shield 233, and at least one container unit C1-C4 contains at least 2 of the retarder, the reflector, and the radiation shield at the same time or at least two different materials at the same time. It is understood that the first and second side plates may not be provided, and the accommodating portion may be surrounded by an outer wall.

The support portion 21 further comprises at least one inner wall circumferentially enclosed around the main axis X and extending between the first and

second side plates

221, 222, in this embodiment the first and second

inner walls

212, 213 are radially inwardly disposed, respectively, and radially defined as a direction perpendicular to the main axis X. The support portion 21 further includes a first cross plate 223 disposed between the first and

second side plates

221, 222 in the direction of the neutron beam N, a third inner wall 214 circumferentially enclosed around the main axis X and extending between the first cross plate 223 and the first side plate 221, and a fourth inner wall 215 circumferentially enclosed around the main axis X and extending from the first cross plate 223 to the second side plate 222. The third inner wall 214 is radially closer to the major axis X than the second inner wall 213, the fourth inner wall 215 is radially between the second inner wall 213 and the third inner wall 214, and the first cross plate 223 extends between the third inner wall 214 and the fourth inner wall 215. The inner surface of the third inner wall 214 is on the same surface as the side wall of the hole 2211 of the first side plate 221, and the third inner wall 214 forms a mounting portion for the transfer tube 111, the first and second cooling tubes D1, D2, and the like. A second cross plate 224 is provided adjacent to the fourth inner wall 215 between the fourth inner wall 215 and the second side plate 222 in the direction of the neutron beam N, the second cross plate 224 extends radially inward from the second inner wall 213, a hole 2241 through which the neutron beam N passes is provided on the second cross plate 224, and the inner wall of the hole 2241 is closer to the main axis X than the inner side of the fourth inner wall 215. It is understood that the second transverse plate may not be provided, the first transverse plate may extend to the outer wall or other inner walls, and a plurality of transverse plates may be provided between the outer wall and the inner wall, and between the inner wall and the inner wall.

In this embodiment, the beam shaper is generally cylindrical, the cross sections of the outer wall and the inner wall in the direction perpendicular to the main axis X are both circular rings surrounding the main axis X and extend parallel to the main axis X, and the side plates and the transverse plates are flat plates extending perpendicular to the main axis X. A first containing unit C1 is formed among the outer wall 211, the first inner wall 212, the first side plate 221 and the second side plate 222, a second containing unit C2 is formed among the first inner wall 212, the second inner wall 213, the first side plate 221 and the second side plate 222, and a third containing unit C3 is formed among the second inner wall 213, the third inner wall 214, the fourth inner wall 215, the first side plate 221, the first horizontal plate 223 and the second horizontal plate 224.

In this embodiment, a PE block 241 having a corresponding shape is provided in the first accommodation unit C1; the lead block 242 and the PE block 241 are sequentially disposed in the second accommodating unit C2 along the neutron beam N direction, a volume ratio of the lead block to the PE block is less than or equal to 10, and an interface of the lead block and the PE block is perpendicular to the neutron beam N direction, which can be understood as other ratios or other distributions. The radiation shield 233 in this embodiment includes a neutron shield and a photon shield, the PE block 241 acting as a neutron shield, and the lead block 242 acting as both the reflector 231 and photon shield.

In this embodiment, the lead block 242, the aluminum alloy block 243, the teflon block 244, and the PE block 241 are provided in the third containing unit C3, the aluminum alloy block 243 and the teflon block 244 are integrally provided to include at least one cone-like shape, the PE block 241 is provided adjacent to the second horizontal plate 224, the lead block 242 fills the remaining region, and the aluminum alloy block 243 and the teflon block 244 integrally divide the lead block 242 in the third containing unit C3 into two parts. The aluminum alloy block 243 and the teflon block 244 are respectively used as the first and second supplementary parts of the retarder 232, so that the manufacturing cost of the retarder can be reduced, meanwhile, the beam quality is not greatly influenced, the first and second supplementary parts are integrally arranged to comprise at least one cone-shaped shape, and better beam quality and treatment effect can be obtained. The teflon block 244 has a better fast neutron absorption effect at the same time, and can reduce the fast neutron content in the beam. The lead 242 serves as both the reflector 231 and the photon shield. The PE block 241 serves as a neutron shield, and it is understood that the PE block may not be provided.

Referring to fig. 6, in the present embodiment, the aluminum alloy block 243 and the teflon block 244 are sequentially disposed along the neutron beam N direction, the aluminum alloy block 243 and the teflon block 244 are integrally disposed in two conical shapes adjacent to each other in opposite directions, the aluminum alloy block 243 is also disposed in two conical shapes adjacent to each other in opposite directions, the aluminum alloy block 243 includes a first conical portion 2431 and a second conical portion 2432 sequentially disposed along the neutron beam N direction, the radial dimension of the outer contour of the first conical portion 2431 gradually increases along the overall trend of the neutron beam N direction, the second conical portion 2432 is connected to the first conical portion 2431 at the position where the radial dimension of the outer contour of the first conical portion 2431 is maximum, and the radial dimension of the outer contour of the second conical portion 2432 gradually decreases along the overall trend of the neutron beam N direction. The teflon block 244 is adjacent to the second cone portion 2432 at the position where the radial dimension of the outer contour of the second cone portion 2432 is the smallest, the radial dimension of the outer contour of the teflon block 244 gradually decreases along the whole trend of the neutron beam N direction, and the teflon block 244 contacts with the PE block 241 at the position where the radial dimension of the outer contour is the smallest. The cross-sectional profiles of the aluminum alloy block 243 and the teflon block 244 in the plane along the major axis X are trapezoids or polygons. The aluminum alloy block 243 has a first side a1 contacting the lead block 242 at the first taper portion 2431, a second side a2 contacting the lead block 242 and a third side A3 contacting the graphite block 244 at the second taper portion 2432, and a fourth side a4 contacting the third inner wall 214, the fourth inner wall 215 and the first cross plate 223 at the first and second taper portions in common, and in this embodiment, the fourth side a4 is a stepped surface. The teflon block 244 has a fifth side a5 contacting the aluminum alloy block 243, a sixth side a6 contacting the lead block 242, a seventh side a7 contacting the fourth inner wall 215, and an eighth side A8 contacting the PE block 241. Wherein the third side A3 and the fifth side a5 are adjacent and serve as an interface of the aluminum alloy block 243 and the teflon block 244, which is perpendicular to the neutron beam N direction in this embodiment. In this embodiment, the volume ratio of the aluminum alloy block 243 to the teflon block 244 is 5-20, and it can be understood that other ratios or other distributions can be adopted according to the neutron beam required for treatment, such as different irradiation depths.

A fourth containing unit C4 is formed in a region surrounded by the fourth inner wall 215 from the first cross plate 223 to the second cross plate 224 in the neutron beam N direction, and the fourth containing unit C4 is radially adjacent to the third containing unit C3. In this embodiment, the magnesium fluoride blocks 245 are provided in the fourth containing unit C4 as a basic portion of the retarder 232, and the magnesium fluoride blocks 245 contain Li-6, which can be a thermal neutron absorber, so that the first and second supplementary portions of the retarder provided in the third containing unit C3 surround the basic portion of the retarder provided in the fourth containing unit C4. The magnesium fluoride block 245 is generally columnar and comprises a first end face a9 and a second end face a10 which are substantially perpendicular to the direction of the neutron beam N, the first end face a9 and the second end face a10 are sequentially arranged along the direction of the neutron beam, the first end face a9 faces the first side plate 221 and is provided with a central hole 2451, the central hole 2451 is used for accommodating the transmission tube 111, the first cooling tube D1, the second cooling tube D2 and the target T, and the like, the central hole 2451 is a cylindrical hole, a side wall 2451a of the central hole and the inner surface of the third inner wall are on the same surface, and the radial distance L1 from the third inner wall 214 to the principal axis X is smaller than the radial distance L2 from the fourth inner wall 215 to the principal axis X, so that the target T is surrounded by the basic part of the retarder 232, neutrons generated by the target T can be effectively slowed down in all directions, and the neutron flux and. The lead plate 246 is arranged between the magnesium fluoride block 245 and the second transverse plate 224, the lead plate 246 is used as a photon shield, lead can absorb gamma rays released from the retarder, and the thickness of the lead plate 246 in the direction of the neutron beam N is less than or equal to 5cm, so that neutrons passing through the retarder are not reflected.

It is understood that PE as the neutron shield in this embodiment may be replaced with other neutron shielding materials; lead as a photon shield can be replaced by other photon shielding materials; lead as a reflector can be replaced by other materials with strong neutron reflecting capacity; the magnesium fluoride as the basic part of the retarder can be replaced by other materials with large fast neutron action section and small epithermal neutron action section; li-6 as a thermal neutron absorber can be replaced by other materials with large cross section for the action of thermal neutrons; the aluminum alloy as the first supplement part of the retarder can be replaced by at least one material of Zn, Mg, Al, Pb, Ti, La, Zr, Bi, Si and C, and the material which is easy to obtain is selected, so that the manufacturing cost of the retarder can be reduced, and meanwhile, the retarder has a certain neutron retarding effect and does not have great influence on the beam quality; the Teflon serving as the second supplement part of the retarder can be replaced by graphite and the like, and the second supplement part is made of materials with better fast neutron absorption effect than the first supplement part, so that the fast neutron content in the beam can be reduced. It will be appreciated that the same material may be used for at least two of the first and second complementary and basic portions of the retarder body.

Referring to fig. 7 and 8, the supporting portion 21 is further provided with a radial partition 210, the plane of the radial partition 210 extends through the main axis X to divide each containing unit C1-C3 into at least two sub-areas in the circumferential direction, so that the PE block, the lead block, the aluminum alloy block and the graphite block arranged in each containing unit C1-C3 are divided into at least two sub-modules in the circumferential direction. In this embodiment, a first radial partition 2101 is disposed between the first side plate 221 and the second side plate, extending from the outer wall 211 to the second inner wall 213; a second radial partition 2102 is disposed between the first side plate 221 and the second cross plate 224, extending from the second inner wall 213 to the third inner wall 214 or the fourth inner wall 215. In the embodiment, the number of the first radial partition plates is 8, and the number of the second radial partition plates is 4, and the first radial partition plates and the second radial partition plates are evenly distributed along the circumferential direction; the first radial partition plate and the second radial partition plate are both flat plates, and 4 of the second radial partition plates and 4 of the first radial partition plates are on the same plane; it is understood that the radial partitions may be in other numbers or in other arrangements, or no radial partitions may be provided.

In this embodiment, the radial partition plate 210, the outer wall 211, the first transverse plate 223 and the first, second, third and fourth

inner walls

212 and 215 are integrated, and the main frame 21a is made of aluminum alloy, which has better mechanical properties and short half-life of the radioactive isotope generated after being activated by neutrons. The method can adopt a casting process and a formwork integrated molding, wherein a wooden mold or an aluminum mold is selected as a template, red sand or resin sand is selected as a sand core, and a mode commonly used in the industry is selected as a specific process. Since casting is accompanied by draft, machining requires its complete removal depending on design and beam quality requirements. The structural form and the casting process enable the frame structure to have the advantages of good integrity, high rigidity and high bearing capacity. All corners are rounded off in view of the machining tool limitations and the stress concentration on the right-angled sides. Or rolling and welding the plates or forging an aluminum alloy cylinder, and then machining and forming the cylinder. The main frame 21a is connected to the second horizontal plate 224 by bolts, first threaded holes are uniformly machined in the end surface of the fourth inner wall 215 facing the second side plate 222, first through holes are uniformly machined in the position of the second horizontal plate 224 corresponding to the first threaded holes, and bolts pass through the first through holes and are connected to the first threaded holes. Considering the assembly of the bolt, the aperture of the first through hole is slightly larger than that of the first threaded hole, and the number of the first threaded holes and the number of the first through holes can meet the requirement of connection strength. The first and

second side plates

221, 222 and the second transverse plate 224 are made of lead-antimony alloy, lead can further shield radiation, and the strength of the lead-antimony alloy is high. The outer contours of the first and

second side plates

221, 222 are identical to the outer contour of the outer wall 211. The first side plate 221, the second side plate 222 and the second transverse plate 224 are connected with the main frame through bolts, second threaded holes are machined in the end faces, facing the first side plate, the second side plate and the second transverse plate, of the inner wall of the main frame 21a respectively, second through holes are machined in the positions, corresponding to the second threaded holes, of the first side plate 221, the second side plate 222 and the second transverse plate 224 respectively, the hole diameter of each second through hole is slightly larger than that of each second threaded hole in consideration of assembly of the bolts, and the number of the second threaded holes and the number of the second through holes can meet connection strength.

It can be understood that, in this embodiment, as long as the materials of the main frame, the side plates, and the end plates (the second transverse plate) have certain strength and the half-life of the radioisotope generated after neutron activation is short (for example, less than 7 days), the material properties of the main frame can satisfy the requirement of supporting the beam shaper, such as aluminum alloy, titanium alloy, lead-antimony alloy, cobalt-free steel, carbon fiber, PEEK, and high molecular polymer; the side plates, the end plates (second transverse plates) and the main frame can be detachably connected or non-detachably connected, and when the side plates and the end plates are detachably connected, all parts of the main body part can be conveniently replaced. The beam shaper of the present embodiment may have other configurations of the support portion and the body portion filling the support portion.

In the construction, the main frame 21a is first placed in the mounting hole provided in the beam shaper support, and the outer wall 211 of the main frame 21a and the beam shaper support are connected by bolts or the like. Then, the main body part is filled and the first side plate, the second side plate and the second transverse plate are installed, and the corresponding areas can be integrally filled due to the fact that the density of PE, aluminum alloy and graphite is small; the lead is heavier, so that the lead can be manually filled in a sub-slice mode along the N direction of the neutron beam or can be integrally filled by means of machinery; the magnesium fluoride may also be filled in bulk or in pieces. After the beam shaper is installed, other components such as a transmission tube, a target material, a collimator and the like are installed, the collimator 30 is arranged at the rear part of a beam outlet, the hyperthermo neutron beam coming out of the collimator 30 irradiates the patient 200, and the hyperthermo neutron beam is slowed down into thermal neutrons to reach the tumor cells M after passing through a shallow normal tissue. In this embodiment, the collimator is fixed to the main frame 21a by bolts or the like, third threaded holes are reserved on the end surface of the second inner wall 213 facing the second side plate, third through holes are uniformly machined in positions on the second side plate 222 corresponding to the third threaded holes, the hole diameter of the third through holes is slightly larger than that of the third threaded holes in consideration of the assembly of the bolts, and the number of the third threaded holes and the third through holes satisfies the connection strength. It will be appreciated that the collimator 30 may be fixed by other means of attachment, and that the collimator 30 may be eliminated or replaced by other structures, with the neutron beam exiting the beam outlet and directed towards the patient 200. In this embodiment, a radiation shield 50 is disposed between the patient 200 and the beam outlet to shield the beam exiting the beam outlet from normal tissue of the patient, although it is understood that the radiation shield 50 may or may not be disposed.

The "column" or "column-shaped" in the embodiment of the present invention refers to a structure in which the overall trend of the outer contour of one side of the outer contour to the other side of the outer contour along the direction shown in the figure is basically unchanged, one of the contour lines of the outer contour may be a line segment, such as a corresponding contour line of a cylindrical shape, or an arc close to the line segment with a larger curvature, such as a corresponding contour line of a spherical shape with a larger curvature, and the entire surface of the outer contour may be in smooth transition, or in non-smooth transition, such as a plurality of protrusions and grooves are formed on the surface of the cylindrical shape or the spherical shape with a larger curvature.

The "cone" or "cone-shaped" in the embodiments of the present invention refers to a structure in which the overall trend of the outer contour gradually decreases from one side to the other side along the direction shown in the figure, one of the contour lines of the outer contour may be a line segment, such as a corresponding contour line in a cone shape, or may be an arc, such as a corresponding contour line in a sphere shape, and the entire surface of the outer contour may be in a smooth transition, or may be in a non-smooth transition, such as a large number of protrusions and grooves are made on the surface in a cone shape or a sphere shape.

Although illustrative embodiments of the invention have been described above to facilitate the understanding of the invention by those skilled in the art, it should be understood that the invention is not limited to the scope of the embodiments, and that various changes will become apparent to those skilled in the art within the spirit and scope of the invention as defined and defined in the appended claims.

Claims

1. A beam shaper for a neutron capture therapy system, the neutron capture therapy system comprising a neutron generating device including an accelerator and a target, a charged particle beam generated by acceleration of the accelerator interacting with the target to generate neutrons, the neutrons forming a neutron beam, the neutron beam defining a principal axis, the beam shaper comprising a moderator decelerating neutrons generated by the neutron generating device to a epithermal neutron energy region, a reflector surrounding the moderator and directing neutrons offset from the principal axis back to the principal axis to increase the epithermal neutron beam intensity, and a radiation shield for shielding leaked neutrons and photons to reduce the normal tissue dose in non-irradiated regions, characterized in that the moderator comprises a base portion and a supplemental portion surrounding the base portion, the beam shaper also includes a support for supporting the beam shaper, the support including a wall surrounding the principal axis, the base portion and the supplemental portion being of different materials and being spaced apart by the wall.

2. The beam shaper for a neutron capture therapy system of claim 1, wherein the walls comprise a first wall, a second wall and a cross plate connecting the first wall and the second wall, the first wall, the second wall and the cross plate being sequentially arranged along the neutron beam direction and circumferentially enclosed around the neutron beam direction, the cross plate extending perpendicular to the neutron beam direction, the first wall being used for mounting a transmission tube of the accelerator, and the second wall forming a substantially partial accommodation cavity of the retarder; the material of the basic part comprises D₂O、Al、AlF₃、MgF₂、CaF₂、LiF、Li₂CO₃Or Al₂O₃The basic portion contains Li-6, and the basic portion simultaneously serves as the thermal neutron absorber.

3. The beam shaper for a neutron capture therapy system according to claim 2, wherein the base portion comprises first and second end surfaces substantially perpendicular to the neutron beam direction, the first and second end surfaces being arranged in series along the neutron beam direction, the first end surface being provided with a central aperture for receiving the transport tube and the target material, the radial distance from the first wall to the main axis being smaller than the radial distance from the second wall to the main axis.

4. The beam shaper for a neutron capture therapy system according to claim 3, wherein a shield plate is disposed adjacent to the second end surface, the shield plate being a lead plate, the shield plate having a thickness in the direction of the neutron beam of less than or equal to 5 cm.

5. The beam shaper for a neutron capture therapy system according to claim 1, wherein the support further comprises a radial baffle that divides the supplemental portion into at least two sub-modules in a circumferential direction around the main axis, a plane in which the radial baffle lies extending through the main axis, the at least two sub-modules being spaced apart by the radial baffle.

6. The beam shaper for a neutron capture therapy system according to claim 1, wherein the supplemental portion comprises first and second adjoining supplemental cells, the base portion, the first and second supplemental cells each being of a different material, the base portion being cylindrical, the first and second supplemental cells being arranged overall to comprise at least one pyramidal shape.

7. The beam shaper for a neutron capture therapy system according to claim 6, wherein the material of the first supplemental unit comprises at least one of Zn, Mg, Al, Pb, Ti, La, Zr, Bi, Si, C, and the material of the second supplemental unit is Teflon or graphite.

8. The beam shaper for a neutron capture therapy system according to claim 6, wherein the first and second complementary units are arranged in sequence along the neutron beam direction, and the first and second complementary units are integrally arranged in two cone shapes that are adjacent to each other in opposite directions.

9. The beam shaper for a neutron capture therapy system of claim 6, the first supplementing unit is arranged into two cone shapes which are mutually adjacent in opposite directions, the first supplementing unit comprises a first cone part and a second cone part which are sequentially arranged along the neutron beam direction, the radial dimension of the outer contour of the first cone part gradually increases along the overall trend of the neutron beam direction, the second taper portion is connected with the first taper portion at a position where a radial dimension of an outer contour of the first taper portion is largest, the radial dimension of the outer contour of the second cone part gradually decreases along the overall trend of the neutron beam direction, the second replenishing unit adjoins the second cone portion at a location where the radial dimension of the outer contour of the second cone portion is smallest, the radial dimension of the outer contour of the second supplementary unit gradually decreases along the overall trend of the neutron beam direction.

10. The beam shaper for a neutron capture therapy system of claim 9, the cross section outline of the first supplementary unit and the second supplementary unit along the plane where the main shaft is located is a trapezoid or a polygon, the first supplement unit has a first side in contact with the reflector at the first taper portion, a second side in contact with the reflector and a third side in contact with the second supplement unit at the second taper portion, and a fourth side in contact with the wall at both the first and second taper portions, the second supplementary unit having a fifth side in contact with the first supplementary unit, a sixth side in contact with the reflector, a seventh side in contact with the wall, the third side and the fifth side are adjacent and used as interfaces of the first supplementary unit and the second supplementary unit, and the interfaces are perpendicular to the neutron beam direction.