RU2783500C1 - Neutron capture therapy system - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: neutron capture therapy system comprises a neutron generation apparatus and a beam-forming unit. The neutron generation apparatus comprises an accelerator and a target. The beam of charged particles, generated when the accelerator accelerates, interacts with the target, generating neutrons. The neutrons form a neutron beam passing along the main axis. The beam-forming unit comprises a support part and a base part filled inside the support part.

EFFECT: prevented strain on and damage to the material of the beam-forming unit, improved flow and quality of the neutron sources.

14 cl, 9 dwg, 1 tbl

Description

BACKGROUND OF THE INVENTION

The field of technology to which the invention belongs

The present invention relates to a radiation exposure system and in particular to a neutron capture therapy system.

BACKGROUND OF THE INVENTION

With the development of atomic technology, radiotherapy, using such means as cobalt-60, linear accelerators and electron beams, has become one of the main means of treating cancer. However, traditional photon or electron therapy suffers from the physical limitations of radioactive rays; for example, many healthy tissues in the path of the beam will be damaged when the tumor cells are destroyed. On the other hand, the sensitivity of tumor cells to radioactive beams varies greatly, therefore, in most cases, traditional radiation therapy is ineffective in the treatment of radioresistant malignant tumors (such as glioblastoma multiforme and melanoma).

In order to reduce radiation damage to healthy tissue surrounding the tumor site, radiation therapy for chemotherapy uses targeted therapy. While for tumor cells with high radioresistance, radiation sources with high relative biological efficiency (RBE) have also been developed, including proton therapy, heavy particle therapy, and neutron capture therapy. Among them, neutron capture therapy combines targeted therapy with OBE such as boron neutron capture therapy (BNCT). Due to the specific grouping of boron-containing pharmaceuticals in tumor cells and fine tuning of the neutron beam, BNCT appears to be a better choice for cancer treatment than traditional radiation therapy.

Boron Neutron Capture Therapy (BNCT) takes advantage of the fact that pharmaceuticals containing boron (B-10) have a high neutron capture cross section and produce heavy charged particles ^4He and 7Li via ^{10V (n,α)7 neutron} capture. Li and nuclear fission reactions. As illustrated in FIG. 1 and 2, which shows a schematic drawing of a BNCT and the formula for a nuclear neutron capture reaction of ¹⁰ V (n, α) ⁷ Li, two charged particles with an average energy of about 2.33 MeV have a high linear energy transfer (LET) and short-range characteristics. The LET and range of the alpha particle are 150 keV/µm and 8 µm, respectively, while for the heavy charged particle ⁷ Li, it is 175 keV/µm and 5 µm, respectively, with the total range of the two particles approximately equal to the cell size. Thus, radiation damage to living organisms can be limited at the cellular level, only tumor cells will be destroyed in the absence of serious damage to normal tissue.

BNCT therapy is also well known as a binary cancer therapy, since its effectiveness depends on the concentration of boron-containing pharmaceuticals and the number of thermal neutrons in the tumor area. Thus, in addition to developing boron-containing pharmaceuticals, improving the flux and quality of the neutron source plays an important role in BNCT therapy research.

Therefore, there is a need to create a new technical solution to the above problem.

DISCLOSURE OF THE INVENTION

In order to improve the flux and quality of neutron sources, one aspect of the present invention provides a neutron capture therapy system comprising a neutron generation device and a beam forming unit, wherein the neutron generation device comprises an accelerator and a target, a charged particle beam generated by accelerating the accelerator interacts with the target to generate neutrons, neutrons form a neutron beam passing along the main axis, the beam forming unit contains a support part and a main part filled inside the support part, the main part contains a moderator, a reflector and a radiation shield, the moderator is configured to slow down the neutrons generated from the target to energy range of epithermal neutrons, the reflector surrounds the moderator and directs the deviating neutrons back to the main axis to increase the intensity of the epithermal neutron beam, while the radiation shield is designed to screen outflowing neutrons and photons, which would reduce the dose to normal tissues in the non-irradiated area. The support part is designed to prevent deformation and damage to the material of the main part, so as to avoid affecting the change of the target and the quality of the beam.

At the same time, the supporting part contains an outer wall, closed in a circle around the main axis, the outer wall forms a containing part, the main part is located in the containing part, the containing part contains at least one containing block, each containing block containing at least one of the moderator, reflector and radiation screen.

In addition, the support part further comprises a first side plate and a second side plate, respectively located on both sides of the outer wall in the direction of the neutron beam and connected to the outer wall, at least one transverse plate located between the first side plate and the second side plate in the direction neutron beam, and at least one inner wall, closed in a circle around the main axis and passing between the first side plate and the second side plate or between the transverse plate and the first / second side plate or between the transverse plates, the first side plate is provided with an opening for passing of the accelerator transmitting tube, a hole is provided in the second side plate for forming a beam exit, a plurality of enclosing blocks is formed between the outer wall, the inner wall, the transverse plate, the first side plate and the second side plate, the radiation shield contains a neutron e a crane and a photon shield, wherein at least one containment unit accommodates both the moderator/neutron shield and the reflector.

Preferably, the inner wall comprises a first inner wall and a second inner wall, the transverse plate comprises the first transverse plate, the first inner wall extends between the first side plate and the first transverse plate and is intended for mounting the transmission tube, and the second inner wall extends in the direction of the neutron beam from the first transverse plate. plate and is designed to accommodate at least part of the moderator.

In this case, the retarder holds the base part and the auxiliary part, the containing block contains the first containing block and the second containing block located next to each other, the base part is placed in the first containing block, the base part is provided with a central hole at the end facing the first side plate, the central hole designed to accommodate the transmission tube and the target, the auxiliary part and at least part of the reflector are placed in the second containing block, the first containing block is surrounded by the second inner wall, and the radial distance from the first inner wall to the main axis is less than the radial distance from the second inner wall to the main axis . The core of the moderator surrounds the target so that neutrons generated from the target can be effectively moderated in all directions, further improving neutron flux and beam quality.

In addition, the material of the base part is magnesium fluoride containing Li-6, the base part is also designed as a thermal neutron absorber, the auxiliary part contains the first auxiliary block and the second auxiliary block, the material of the first auxiliary block is aluminum alloy, the material of the second auxiliary block is teflon, reflector material - lead, while the reflector is also made as a photon screen; parts, the first auxiliary block and the second auxiliary block are arranged in series in the direction of the neutron beam, and the boundary between the first auxiliary block and the second auxiliary block is perpendicular to the direction of the neutron beam. An aluminum alloy block and a Teflon block are respectively provided as the first auxiliary block and the second auxiliary block of the moderator, so that the manufacturing cost of the moderator can be reduced without significantly degrading the beam quality. The first auxiliary block and the second auxiliary block are made as one whole in the form of two cone-shaped shapes located next to each other in opposite directions, which allows to achieve a better beam quality and a better treatment effect. Teflon also has a better fast neutron absorption effect, so that the content of fast neutrons in the beam can be reduced.

At the same time, the lead shielding plate is additionally located between the magnesium fluoride block in the first containing block and the positioning ring / retaining ring, the base part and the shielding plate are sequentially located in the direction of the neutron beam, the positioning ring or retaining ring is made of a material with a short half-life of the activated nucleus, formed as a result of the activation reaction, the material of the shielding plate is lead, and the thickness of the lead shielding plate in the direction of the neutron beam is less than or equal to 5 cm, so that the neutrons passing through the moderator are not reflected, and the lead can absorb gamma rays coming out of the moderator . The outer wall, at least one of the inner walls and at least one of the cross plates are integrated with the main frame, the half-life of radioactive isotopes generated by the materials of the main frame, the first side plate and the second side plate after neutron activation is less than 7 days , wherein the material of the main frame, the first side plate, and the second side plate is aluminum alloy, titanium alloy, lead antimony alloy, cast aluminum, cobalt-free steel, carbon fiber, PEEK, or high polymer. When an aluminum alloy is selected as the main frame material, the aluminum alloy has suitable mechanical properties and a short half-life of radioactive isotopes generated by the aluminum alloy after the aluminum alloy is activated by neutrons. When a lead-antimony alloy is selected as the material of the first side plate and the second side plate, lead can further shield radiation, and the lead-antimony alloy has a relatively high strength.

Preferably, the containing block comprises a third containing block, a neutron shield, and at least a part of the reflector is placed in the third containing block, while the material of the neutron shield is polyethylene, the material of the reflector is lead, the reflector is also made as photon screens, the reflector and the neutron shield are in the third containing block. block are sequentially located in the direction of the neutron beam, and the boundary between the reflector and the neutron screen in the third containing block runs perpendicular to the direction of the neutron beam.

Preferably, the support part further comprises radial baffles that circumferentially divide the containing block into a plurality of sub-regions, the radial baffles are located between the first side plate and the second side plate or between the transverse plate and the first/second side plate or between the transverse plates and extend from the outer wall to the inner wall or extends between two inner walls.

Another aspect of the present invention provides a beam forming unit for a neutron capture therapy system. The neutron capture therapy system contains a neutron generation device, the neutrons generated by the neutron generation device form a neutron beam, the beam formation unit can adjust the beam quality of the neutron beam, the beam formation unit contains a support part and a main part filled inside the support part, while the support part forms at least one containing block, and each containing block contains at least a part of the main part. The support part is designed to prevent deformation and damage to the material of the main part, so as to avoid affecting the change of the target and the quality of the beam.

A third aspect of the present invention provides a beam forming unit for a neutron capture therapy system. The neutron capture therapy system comprises a neutron generation device, wherein the neutron generation device comprises an accelerator and a target, a beam of charged particles generated during acceleration of the accelerator interacts with the target to generate neutrons, neutrons form a neutron beam, the neutron beam passes along the main axis, the beam formation unit contains a moderator, a reflector and a radiation shield, the moderator is configured to slow the neutrons generated by the neutron generation device to the epithermal neutron energy range, the reflector surrounds the moderator and directs the deviated neutrons back to the main axis to increase the intensity of the epithermal neutron beam, the radiation shield is designed to shield the escaping neutrons and photons to reduce the dose to normal tissues in the non-irradiated region, the moderator contains a base part and an auxiliary part surrounding the base part, the beam forming unit additionally contains a support cup A device for supporting the beam forming unit, wherein the support part comprises a wall around the main axis, and the base part and the auxiliary part are made of different materials and are separated by a wall. The support part is designed to prevent deformation and damage to the material of the main part of the beam forming unit, so as to avoid affecting the change of the target and the quality of the beam. For the auxiliary part, an easily accessible material is chosen, which makes it possible to reduce the cost of manufacturing the moderator, to implement a specific moderation of neutrons, without a significant deterioration in the quality of the beam.

Preferably, the wall comprises a first wall, a second wall and a transverse plate connecting the first wall and the second wall, which are arranged in series in the direction of the neutron beam and are closed in a circle around the direction of the neutron beam, the transverse plate runs perpendicular to the direction of the neutron beam, the first wall is intended for mounting the transmission tube accelerator, the second wall forms a containing cavity for the base part of the moderator, the material of the base part contains at least one of D ₂ O, Al, AlF ₃ , MgF ₂ , CaF ₂ , LiF, Li ₂ CO ₃ , or Al ₂ O ₃ having a large cross section for interaction with fast neutrons and a small cross section for interaction with epithermal neutrons, which provides a suitable moderation; the base part contains Li-6, and the base part is also made as a thermal neutron absorber.

In this case, the base part contains the first end surface and the second end surface, which are approximately perpendicular to the direction of the neutron beam, the first end surface and the second end surface are sequentially located in the direction of the neutron beam, the first end surface is provided with a central hole, the central hole is designed to accommodate the transmitting tube and the target , the radial distance from the first wall to the main axis is less than the radial distance from the second wall to the main axis, while the base part of the moderator surrounds the target, so that the neutrons generated by the target can be effectively slowed down in all directions, which can further improve the neutron flux and beam quality . The shielding plate is located near the second end surface, and the shielding plate is a lead plate, and the lead can absorb gamma rays emitted by the moderator. The thickness of the shielding plate in the direction of the neutron beam is less than or equal to 5 cm, so that neutrons passing through the moderator are not reflected.

In addition, preferably, the supporting part additionally contains radial partitions dividing the auxiliary part into at least two submodules along a circle around the main axis, and the plane in which the radial partition is located passes through the main axis, and at least two submodules are separated by a radial partition.

In addition, preferably, the auxiliary part includes the first auxiliary block and the second auxiliary block located next to each other, the base part, the first auxiliary block and the second auxiliary block are made of three different materials, the base part is cylindrical, while the first auxiliary block and the second auxiliary block the block is made as a whole in a shape containing at least one cone shape, which allows you to get a better beam quality and a better treatment effect.

The material of the first auxiliary block includes at least one of Zn, Mg, Al, Pb, Ti, La, Zr, Bi, Si and C, and the material of the second auxiliary block is Teflon or graphite. The first auxiliary block and the second auxiliary block are arranged in series in the direction of the neutron beam, and the first auxiliary block and the second auxiliary block are made as one unit in the form of two conical shapes located next to each other in opposite directions. For the first auxiliary block of the moderator, an easily accessible material is selected, which makes it possible to reduce the cost of manufacturing the moderator, to implement a specific moderation of neutrons, without a significant deterioration in the quality of the beam. For the second auxiliary block, a material with a better absorption effect is selected than the material of the first auxiliary block, which makes it possible to reduce the content of fast neutrons in the beam.

In this case, the first auxiliary module is made in the form of two cone-shaped shapes located next to each other in opposite directions, the first auxiliary module contains the first cone-shaped section and the second cone-shaped section, successively located in the direction of the neutron beam, the radial size of the outer contour of the first cone-shaped section gradually increases in direction of the neutron beam as a whole, the second cone-shaped section is connected to the first cone-shaped section in a position where the radial size of the outer contour of the first cone-shaped section is maximum, while the radial size of the outer contour of the second cone-shaped section gradually decreases in the direction of the neutron beam as a whole, the second auxiliary unit is located nearby with the second tapered section at a position where the radial dimension of the outer contour of the second tapered section is minimal, and the radial dimension of the outer contour of the second auxiliary block is gradually reduced in the direction of the neutron beam as a whole.

In addition, the contours of the cross section of the first auxiliary block and the second auxiliary block in the plane where the main axis is located, are irregular quadrangles or polygons, and the first auxiliary block contains the first side in contact with the reflector on the first cone section, the second side in contact with the reflector , and a third side in contact with the second auxiliary block on the second cone section, and a fourth side in contact with the wall on both the first cone section and the second cone section, the second auxiliary block includes a fifth side in contact with the first auxiliary block, a sixth side in contact with reflector, and the seventh side in contact with the wall, the third side and the fifth side are located side by side and are made as a boundary between the first auxiliary block and the second auxiliary block, the boundary being perpendicular to the direction of the neutron beam.

A fourth aspect of the present invention provides a beamformer for a neutron capture therapy system. The neutron capture therapy system contains a neutron generation device, the neutrons generated by the neutron generation device form a neutron beam, the neutron beam passes along the main axis, the beam formation unit can adjust the quality of the neutron beam, the beam formation unit contains a support part and a main part filled inside the support part, the support part includes a support frame, the support frame is formed by heating a workpiece of material with a heating equipment and then forging into a cylinder with a forging equipment, the cylinder is machined after rough machining and heat treatment. The support part is designed to prevent deformation and damage to the material of the main part, so as to avoid affecting the change of the target and the quality of the beam. The support frame requires several forging procedures and fewer heating periods, has a homogenized structure and suitable forging characteristics, and saves raw materials. The workpiece material is heated before forging, so that the deformation resistance can be reduced and the ductility can be improved. After rough machining of the forged cylinder, the overall material properties of the support frame after heat treatment can be ensured.

Wherein, the support frame material is an aluminum alloy, the mass fraction of Cu in the aluminum alloy is ≤7%, which can meet the requirement of a short half-life of radioactive isotopes generated by the support frame after neutron activation. For the support frame, the tensile strength is ≥150MPa and the yield strength is ≥100MPa so that the support frame can support the main body of the beam forming unit. Aluminum alloy is a malleable aluminum alloy. The forging equipment is free forging equipment, and the free forging equipment includes heading and drawing equipment. The structure and properties of the aluminum alloy are changed by free forging using the plastic forming method, which further saves raw materials.

At the same time, the heating equipment is a radiant resistance heating furnace, air circulates in the furnace to maintain an accurate and uniform temperature, the temperature deviation of the furnace is ±10°C, the maximum initial forging temperature is 520°C, the final forging temperature is 450°C, and permissible limiting temperature 530°C. The heating time can be determined according to the dissolution of the strengthening phase and the homogenization of the structure. In this state, appropriate ductility can be obtained, and the forging performance of the aluminum alloy can be improved.

In this case, the main part contains a moderator, a reflector and a radiation shield, the moderator slows down the neutrons generated by the neutron generation device to the energy range of epithermal neutrons, the reflector surrounds the moderator and directs neutrons deviating from the main axis back to the main axis to increase the intensity of the epithermal neutron beam, the radiation shield is designed to shield leaking neutrons and photons in order to reduce the dose to normal tissues in the non-irradiated zone, the support frame forms at least one enclosing block, with each enclosing block containing at least part of the main part.

In addition, the containing block contains the first containing block containing at least a part of the moderator, the first containing block is located in the center of the support frame in the radial direction, while rough machining is drilling holes in the areas of the cylinder corresponding to the first containing block. When the heat treatment is carried out directly on the cylinder, it is difficult to ensure the required characteristics of the material in the center of the cylinder. Thus, a hole is drilled in the center position (i.e., in the cylinder regions corresponding to the first containing block) of the forged cylinder by rough machining, then deep heat treatment is performed so that the support frame can be close to the center position (to form the body frame of the first containing block) and the general properties of the material after heat treatment. In addition, the first housing block accommodates the moderator, so that the moderator can be maintained, and deformation and damage of the moderator is prevented so as to avoid affecting target change and beam quality.

In this case, the containing block contains a second containing block containing at least one of the moderator, reflector and radiation shield, the support frame contains an outer wall closed in a circle around the main axis, and at least one inner wall, the second containing block is formed between the outer wall and the inner wall or between the inner walls, wherein the rough machining further comprises pre-machining the cylinder regions corresponding to the second containing block. It is contemplated that rough machining may not be performed on the cylinder regions corresponding to the second containing block in order to prevent the regions from being easily deformed due to thinness during post-rough machining heat treatment.

Meanwhile, the heat treatment comprises solution treatment and aging treatment, aluminum after solution treatment is kept at a certain temperature for a certain time, and the supersaturated solid solution decomposes, causing a strong increase in the strength and hardness of the alloy.

A fifth aspect of the present invention provides a method for processing a support frame of a beam forming unit, comprising:

heating: heating a workpiece of material that meets the requirements for the materials of the base frame at a certain temperature and for a certain time;

forging: forging heated billet material into a cylinder;

rough machining: drilling a hole in the center of a forged cylinder;

heat treatment: performing heat treatment on a forged body obtained after rough machining; and

Machining: Machining a forged body after heat treatment to obtain a support frame with the final desired shape and size.

The support part is designed to prevent deformation and damage to the material of the main part, so as to avoid affecting the change of the target and the quality of the beam. The base frame requires several forging procedures and fewer heating periods, has a homogenized structure and suitable forging characteristics, and saves raw materials. The workpiece material is heated before forging, which can reduce deformation resistance and improve ductility. A hole is drilled in the center position of the forged cylinder and then heat treated so that the support frame can be close to the center position and the overall material properties after heat treatment can be ensured.

Meanwhile, before the heating step, it is determined that the material of the workpiece satisfies the requirements for the raw material for the support frame; before the forging step, the workpiece material is processed to meet the processing requirements of the forging equipment; forging is free forging including upsetting and drawing, as long as the forging temperature is not lower than the predetermined temperature, static forging is repeated in accordance with the processes of the above two methods to obtain fine grains in the structure, and the forging equipment has the accuracy of forging a workpiece; heat treatment includes solution treatment and aging treatment, aluminum after solution treatment is kept at a certain temperature for a certain time, and the supersaturated solid solution decomposes, causing a strong increase in the strength and hardness of the alloy; after heat treatment, physical and chemical tests and inspections are performed, including dimensional inspection, element inspection, mechanical property testing and non-destructive ultrasonic flaw detection.

In the present invention, the beam forming unit of the neutron capture therapy system makes it possible to prevent deformation and damage to the material of the beam forming unit, improve the flux and quality of neutron sources.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram of the neutron capture reaction by boron;

fig. 2 shows the equation for the nuclear reaction of neutron capture ¹⁰ V (n, ^α ) ⁷ Li;

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

fig. 4 is a schematic diagram of a beamforming unit of a neutron capture therapy system according to an embodiment of the present invention;

fig. 5 is a schematic diagram of the bearing part of FIG. four;

fig. 6 is a schematic exploded view of the moderator of FIG. four;

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

fig. 8 is a schematic diagram of the main frame of FIG. 5 when viewed from a direction opposite to that of the neutron beam N; and

fig. 9 is a block diagram of an embodiment of the main frame of FIG. 5 during processing.

IMPLEMENTATION OF THE INVENTION

Embodiments of the present invention are described in detail below with reference to the accompanying drawings to enable a person skilled in the art to implement the present invention with reference to the text of the description.

As shown in FIG. 3, the neutron capture therapy system in this embodiment is preferably a boron neutron capture therapy system 100, which includes a neutron generation device 10, a beam forming unit 20, a collimator 30, and a treatment table 40. The neutron generation device 10 includes an accelerator 11 and a target. T, while 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 interacts with the target T to generate neutrons, which form the neutron beam, the neutron beam N travels along the main axis X, and the target T is a metal target. The direction of the neutron beam N, described below with reference to the accompanying drawings, is not the actual direction of the neutron beam, but the general trend of the direction of the neutron beam N. Appropriate nuclear reactions are always determined according to characteristics such as the desired neutron yield and energy, available energy accelerated charged particles and current, the materialization of a metal target, among which the most discussed two are ⁷ Li (p, n) ⁷ Be and ⁹ Be (p, n) ⁹ V, and both of which are endothermic reactions. Their energy thresholds are 1.881 MeV and 2.055 MeV respectively. Epithermal keV neutrons are considered ideal neutron sources for BNCT therapy. In theory, bombardment with a lithium target using slightly above threshold protons could produce relatively low energy neutrons, so neutrons could be used clinically without major delays. However, Li (lithium) and Be (beryllium) and threshold energy protons have a low effective cross section. High-energy protons are usually chosen to produce sufficient fluxes of neutrons to cause nuclear reactions. The target, considered ideal, is assumed to have the advantages of high neutron yield, produced neutron energy distribution near the epithermal neutron energy range (see below for details), small high penetrating radiation, safety, low cost, easy access, high temperature resistance, etc. But in fact, no nuclear reactions can satisfy all the requirements. However, as is well known to those skilled in the art, target materials can be made from metals other than Li or Be, such as tantalum (Ta) or tungsten (W), or alloys thereof. The accelerator 11 may be a linear accelerator, a cyclotron, a synchrotron, a synchrocyclotron.

BNCT neutron sources produce only mixed radiation fields, i.e. the beams contain neutrons and photons with low to high energies. As for BNCT in the depth of tumors, with the exception of epithermal neutrons, the larger the residual amount of the radiation beam, the higher the proportion of non-selective dose deposition in normal tissue. Therefore, radiation causing excessive dose should be reduced to the maximum. In addition to air beam quality indicators, the dose is calculated using a human head tissue prosthesis to understand the neutron dose distribution in the human body. Prosthesis beam quality factors are later used as design reference for neutron beams, as detailed below.

The International Atomic Energy Agency (IAEA) has submitted five proposals for air quality factors for BNCT clinical neutron sources. The proposals can be used to differentiate neutron sources and as a reference for selecting neutron production options and designing a beamformer, and are presented as follows:

Epithermal neutron flux >1x10 ⁹ n/cm ² s

Contamination with fast neutrons <2 x10 ^-13 Gy-cm ² /n

Photon pollution <2 x10 ^-13 Gy-cm ² /n

Ratio of thermal and epithermal neutrons <0.05

ratio of epithermal neutron current to flux >0.7>

Note: The epithermal neutron energy range is from 0.5 eV to 40 keV, the thermal neutron energy range is below 0.5 eV, and the fast neutron energy range is above 40 keV.

1. Flux of epithermal neutrons

The flux of epithermal neutrons and the concentration of boron-containing pharmaceuticals at the tumor site together determine the time of clinical therapy. If boron-containing pharmaceuticals are at a high enough concentration at the tumor site, the epithermal neutron flux can be reduced. On the contrary, if the concentration of boron-containing pharmaceuticals in tumors is low, it is necessary that the epithermal neutrons in the high epithermal neutron flux provide sufficient doses to the tumors. This epithermal neutron flux standard from the IAEA is over ¹⁰⁹ epithermal neutrons per square centimeter per second. In a given flux of neutron beams, therapy time can be approximately controlled to less than an hour using boron-containing pharmaceuticals. Thus, in addition to making patients well-placed and more comfortable during shorter treatment times, the limited residence time of boron-containing pharmaceuticals in tumors can be effectively exploited.

2. Pollution by fast neutrons

An excess dose to healthy tissue produced by fast neutrons is considered contamination. The dose exhibits a positive correlation with the neutron energy, hence the number of fast neutrons in neutron beams should be reduced as much as possible. The dose of fast neutrons per unit of epithermal neutron flux is considered fast neutron contamination and, according to the IAEA, is less than 2*10 ^-13 Gy-cm ² /n.

3. Photon pollution (gamma pollution)

Long-range gamma radiation will selectively accumulate dose in all tissues along the path of the beam, so reducing the amount of gamma radiation is also an extremely important requirement in the development of a neutron beam. The dose of gamma radiation per unit flux of epithermal neutrons is defined as contamination by gamma radiation, which, according to the IAEA, is less than 2*10 ^-13 Gy-cm ² /n.

4. Relationship between thermal and epithermal neutrons

Thermal neutrons decay so quickly and penetrate poorly that they leave most of the energy in the skin tissues after they enter the body. Except for skin tumors such as melanocytoma, thermal neutrons serve as sources of BNCT neutrons, in other cases, such as brain tumors, the number of thermal neutrons must be reduced. In accordance with the IAEA, the ratio of thermal and epithermal neutron fluxes is recommended below 0.05.

5. Ratio of epithermal neutron current to flux

The ratio of epithermal neutron current to flux indicates the direction of the beam, the higher this ratio, the better the forward direction of neutron beams, and neutron beams in the best forward direction can reduce the dose surrounding normal tissue resulting from neutron scattering. In addition, the machining depth is improved as well as the positional position. According to the IAEA, it is better when the ratio of epithermal neutron current to flux is greater than 0.7.

Prosthesis beam quality factors are derived from the dose distribution in the tissue delivered by the prosthesis according to the dose-depth curve of normal tissue and tumors. The following three parameters can be used to compare the various effects of neutron beam therapy.

1. Preferred depth

The tumor dose is equal to the depth of the maximum dose of normal tissue. The dose of tumor cells in a position behind the depth is less than the maximum dose of normal tissue, that is, the capture of neutrons by boron loses its advantages. The preferred depth indicates the permeability of the neutron beams. Calculated in cm: the greater the preferred depth, the greater the depth of the tumor to be treated.

2. Dose level preferred depth

The preferred depth dose level is the tumor dose level at the preferred depth, also equal to the maximum dose level for normal tissue. This may affect the duration of therapy, since the total dose for normal tissue is a factor that can affect the total dose provided for tumors. The higher it is, the shorter the irradiation time for obtaining a certain dose on tumors, calculated by cGy/mA-min.

3. Preferred ratio

The average ratio of doses received by tumors and normal brain surface tissue to the preferred depth is called the preferred ratio. The mean ratio can be calculated using the dose-depth curvilinear integral. The higher the preferred ratio, the better the therapeutic effect of the neutron beams.

In order to provide a comparative reference to the design of the beam forming unit, the following parameters are also provided to evaluate the advantages and disadvantages of expressing neutron beams in the embodiments of the present invention, with the exception of the IAEA air beam quality factors and the above parameters.

1. Irradiation time ≤30 min (proton current for accelerator 10 mA)

2. 30.0 RBE-Gy treatment depth > ≥7 cm

3. Maximum tumor dose ≥60.0 RBE-Gy

4. Maximum dose of normal brain tissue ≤12.5 RBE-Gy

5. Maximum skin dose ≤11.0 RBE-Gy

Note: RBE means relative biological effectiveness. Because photons and neutrons exhibit different biological efficiencies, the above dose should be multiplied by the RBE of different tissues to obtain an equivalent dose.

The neutron beam N generated by the neutron generation device 10 sequentially passes through the beam formation unit 20 and the collimator 30, then is radiated to the patient 200 on the treatment table 40. The beam formation unit 20 is able to control the quality of the neutron beam N generated by the neutron generation device 10, and the collimator 30 is used to concentrate the N beam, so that the N beam can be more accurately targeted when performing treatment. The beam forming unit 20 further comprises a support part 21 (not shown in Fig. 1, described in detail below) and a main part 23 filled inside the support part 21, the support part 21 forms at least one enclosing element C1-C10, each of which contains at least part of the main body 23. The support part can prevent deformation and damage of the material of the main body and affect the replacement of the target and the quality of the beam. The main body 23 contains a moderator 231, a reflector 232, a radiation shield 233. The neutrons generated by the neutron generation device 10 have a wide energy spectrum, and in addition to epithermal neutrons, it is desirable to reduce the number of other types of neutrons and photons as much as possible to meet the needs of treatment, to avoid harm to operators or patients. Therefore, the neutrons exiting the neutron generator 10 must pass through the moderator 231 to adjust the fast neutron energy therein to the epithermal neutron energy region. The moderator 231 is made of a material having a cross section for mainly fast neutron action, but almost no epithermal neutron action, for example, contains at least one of ₂ O, AlF ₃ , Fluental, CaF ₂ , Li ₂ CO ₃ , MgF ₂ and Al ₂ O ₃ . The reflector 232 surrounds the moderator 231 and reflects the neutrons scattered through the moderator 231 back into the neutron beam N to improve neutron utilization, and is made of a material having a high neutron reflectivity such as containing at least one of Pb and Ni. The radiation shield 233 is designed to shield escaping neutrons and photons in order to reduce the dose to normal, non-irradiated tissue. The radiation shield material 233 comprises at least one of a photon shielding material and a neutron shielding material such as photon shielding lead (Pb) and neutron shielding polyethylene (PE). It should be understood that the main body may have other configurations, provided that the epithermal neutron beam required for the treatment can be obtained.

The target T is located between the accelerator 11 and the beam forming unit 20, and the accelerator 11 has a transmission tube 111 that transmits the charged particle beam P. In this embodiment, the transfer tube 111 penetrates the beam formation unit 20 in the direction of the charged particle beam P and successively passes through moderator 231 and reflector 232. The target T is placed in the moderator 231 and is located at the end of the transmission tube 111 to obtain a better quality of the neutron beam. In this embodiment, the first and second cooling tubes D1 and D2 are located between the transmission tube 111 and the moderator 231, and between the transmission tube 111 and the reflector 232, with one end of the first and second cooling tubes D1, D2 respectively connected to the cooling inlet IN (not shown in the figures) and the cooling outlet OUT (not shown in the figures) of the target T, the other ends are connected to an external source of cooling (not shown in the figures). It should be understood that the first and second cooling tubes can be arranged differently in the beamformer and can be dispensed with when the target is placed outside the beamformer.

As shown in FIG. 4 and FIG. 5, the support portion 21 comprises an outer wall 211 circumferentially closed about the main axis X, and a first side plate 221 and a second side plate 222 located respectively on both sides of the outer wall 211 in the direction of the neutron beam N and connected to the outer wall 211, provided a hole 2211 for passing the transmission tube 111 in the first side plate 221, a hole 2221 for forming a beam outlet in the second side plate 222, a housing portion C is formed between the outer wall 211, the first side plate 221 and the second side plate 222, and the main body 23 is located in the containing part C. The containing part C contains at least one containing block C1-C4 (detailed below), each containing block C1-C4 accommodates at least one of the moderator 231, the reflector 232 and the radiation shield 233, at least one containing block C1-C4 accommodates at least two of the moderator, reflector and radiation shield, or accommodates at least two different materials. It is understood that the first side plate and the second side plate may not be used, and the outer wall surrounds the containing part.

The support portion 21 further comprises at least one inner wall circumferentially closed about the major axis X and extending between the first side plate 221 and the second side plate 222. In this embodiment, the first inner wall 212 and the second inner wall 213 are placed inward in the radial direction , and the radial direction is defined as the direction perpendicular to the main axis X. The support part 21 further comprises a first transverse plate 223 located between the first side plate 221 and the second side plate 222 in the direction of the neutron beam N, the third inner wall 214 is closed in a circle around the main axis X and extends between the first transverse plate 223 and the first side plate 221, and the fourth inner wall 215, closed in a circle around the main axis X and extending from the first transverse plate 223 to the second side plate 222. The third inner wall 214 is closer to the main axis X in radial direction than the second inner wall 213, the fourth inner wall 215 is located radially between the second inner wall 213 and the third inner wall 214, and the first transverse 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 opening 2211 in the first side plate 221, and the third inner wall 214 forms a mounting portion for the transmission tube 111, the first cooling tube D1, the second cooling tube D2, and the like. The second transverse plate 224 is located between the fourth inner wall 215 and the second side plate 222 and is adjacent to the fourth inner wall 215 in the direction of the neutron beam N, the second transverse plate 224 extends radially inward from the second inner wall 213, an opening 2241 is provided for passing the neutron beam N into second transverse plate 224, with the inner wall of the opening 2241 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 used, the first transverse plate may extend to the outer wall or another inner wall, and a plurality of The plates may alternatively be located between the outer wall and the inner wall, as well as between the inner walls.

In this embodiment, the entire beam forming unit is cylindrical, the cross sections of the outer wall and the inner wall in the direction perpendicular to the main X axis are rings around the main X axis and run parallel to the main X axis, and the side plates and the cross plate are flat plates. running perpendicular to the main axis X. Of course, other designs are also possible as an alternative. For example, the direction of passage is inclined to the main axis, and the outer contour of the outer wall in the direction perpendicular to the main axis may alternatively be square, rectangular or polygonal, which is convenient for transportation and installation. The first containing block C1 is formed between the outer wall 211, the first inner wall 212, the first side plate 221 and the second side plate 222. The second containing block C2 is formed between the first inner wall 212, the second inner wall 213, the first side plate 221 and the second side plate 222 A third containing block C3 is formed between the second inner wall 213, the third inner wall 214, the fourth inner wall 215, the first side plate 221, the first transverse plate 223, and the second transverse plate 224.

In this embodiment, an appropriately shaped PE block 241 is located in the first containing block C1, the lead block 242 and the PE block 241 are sequentially located in the second containing block C2 in the direction of the neutron beam N, the volume ratio of the lead block to the PE block is less than or equal to 10 , and the boundary between the lead block and the PE block is perpendicular to the direction of the neutron beam N. It is understood that other ratios or other arrangements may be alternative. In this embodiment, the radiation shield 233 comprises a neutron shield and a photon shield, a PE block 241 is configured as a neutron shield, and a lead block 242 is configured as reflectors 232 and a photon shield.

In this embodiment, the lead block 242, the aluminum alloy block 243, the Teflon block 244, and the PE block 241 are located in the third containing block C3, the aluminum alloy block 243 and the Teflon block 244 are integrally formed in a form including at least one cone-shaped, with the PE block 241 adjacent to the second transverse plate 224, the lead block 242 filling the remaining area, and the aluminum alloy block 243 and the Teflon block 244 halving the lead block 242 in the third enclosing block C3. The aluminum alloy block 243 and the Teflon block 244 are respectively configured as the first auxiliary block and the second auxiliary block of the moderator, so that the manufacturing cost of the moderator can be reduced without significantly degrading the beam quality. The first auxiliary block and the second auxiliary block are made in a shape including at least one cone shape, which makes it possible to achieve a better beam quality and a better treatment effect. The Teflon block 244 also has a better fast neutron absorption effect, so that the content of fast neutrons in the beam can be reduced. The output unit 242 is designed as a reflector 232 and a photonic screen. The PE block 241 is designed as a neutron shield. It is understood that a block from PE cannot be deleted.

As shown in FIG. 6, in this embodiment, the aluminum alloy block 243 and the Teflon block 244 are arranged in series in the direction of the neutron beam N, the aluminum alloy block 243 and the Teflon block 244 are formed as two cone-shaped shapes adjacent to each other in opposite directions, the block 243 aluminum alloy block is also made in the form of two cones located next to each other in opposite directions, the aluminum alloy block 243 includes a first cone section 2431 and a second cone section 2432, which are sequentially located in the direction of the neutron beam. N, the radial dimension of the outer contour of the first cone section 2431 gradually increases in the direction of the neutron beam N as a whole, the second cone section 2432 is connected to the first cone section 2431 at a position where the radial dimension of the outer contour of the first cone section 2431 is maximum, and the radial dimension of the outer contour the second cone-shaped section 2432 gradually decreases in the direction of the neutron beam N as a whole. The Teflon block 244 is located adjacent to the second cone section 2432 at a position where the radial dimension of the outer contour of the second cone section 2432 is minimal, the radial dimension of the outer contour of the Teflon block 244 gradually decreases in the direction of the neutron beam N as a whole, and the Teflon block is in contact with the block 241 from PE in the position where the radial dimension of the outer contour is maximum. The cross-sectional contours of the aluminum alloy block 243 and the Teflon block 244 in the plane where the main X-axis is located are irregular quadrangles or polygons. The aluminum alloy block 243 has a first side A1 in contact with the lead block 242 in the first cone section 2431, a second side A2 in contact with the lead block 242, and a third side A3 in contact with the Teflon block 244 in the second cone section 2432, as well as a fourth the side A4 contacting the third inner wall 214, the fourth inner wall 215 and the first transverse plate 223 in the first cone section and the second cone section. In this embodiment, the fourth side A4 is a stepped surface. The Teflon block 244 has a fifth side A5 in contact with the aluminum alloy block 243, a sixth side A6 in contact with the lead block 242, a seventh side A7 in contact with the fourth inner wall 215, and an eighth side A8 in contact with the PE block 241. The third side A3 and the fifth side A5 are adjacent to each other and are configured as a boundary between the aluminum alloy block 243 and the Teflon block 244. In this embodiment, the boundary is perpendicular to the direction of the neutron beam N. In this embodiment, the volume ratio of the aluminum alloy block 243 to Teflon block 244 is between 5 and 20. It is contemplated that alternatively there may be other ratios or other distributions according to the neutron beam required for treatment, such as other irradiation depths.

The area from the first transverse plate 223 to the second transverse plate 224 in the direction of the neutron beam N and surrounded by the fourth inner wall 215 forms the fourth containing block C4, and the fourth containing block C4 is located next to the third containing block C3 in the radial direction. In this embodiment, a magnesium fluoride block 245 is provided in the fourth containing block C4 as the base part of the moderator 231, and the magnesium fluoride block 245 contains Li-6 and is also configured as a thermal neutron absorber, so that the first auxiliary block and the second auxiliary block of the moderator located in the third containing block C3 surround the base part of the moderator located in the fourth containing block C4. The entire magnesium fluoride block 245 is cylindrical, including the first end surface A9 and the second end surface A10, which are approximately perpendicular to the direction of the neutron beam N. The first end surface A9 and the second end surface A10 are sequentially located in the direction of the neutron beam. The first end surface A9 faces the first side plate 221 and is provided with a central hole 2451. The central hole 2451 is designed to accommodate the transmission tube 111, the first cooling tube D1, the second cooling tube D2 and the target T. The central hole 2451 is a cylindrical hole. The side wall 2451a of the central hole is on the same surface as the inner surface of the third inner wall. The radial distance L1 from the third inner wall 214 to the main X-axis is less than the radial distance L2 from the fourth inner wall 215 to the main X-axis, and the base portion of the moderator 231 surrounds the target T so that the neutrons generated by the target T can be effectively slowed down in all directions, so that the neutron flux and beam quality can be further improved. The lead plate 246 is located between the magnesium fluoride block 245 and the second transverse plate 224. The lead plate 246 is designed as a photon shield, the lead can absorb gamma rays emitted by the moderator. The thickness of the shield plate 246 in the direction of the neutron beam N is less than or equal to 5 cm, so that neutrons passing through the moderator are not reflected. It is understood that in the alternative there may be another implementation. For example, the magnesium fluoride block 245 does not contain Li-6, but a separate thermal neutron absorber consisting of Li-6 is located between the magnesium fluoride block 245 and the second transverse plate 224, while the lead plate may alternatively be omitted.

It is contemplated that in this embodiment, the PE that serves as the neutron shield may be replaced by another neutron shielding material; lead, which serves as a photon shield, can be replaced with another photon shielding material; lead, which serves as a reflector, can be replaced by another material with a high ability to reflect neutrons; magnesium fluoride, which serves as the base part of the moderator, can be replaced by another material having a large cross section for interaction with fast neutrons and a small cross section for interaction with epithermal neutrons; Li-6, which serves as an absorber of thermal neutrons, can be replaced by another material having a large cross section for interaction with thermal neutrons; the aluminum alloy which serves as the first sub-unit of the moderator may be replaced by a material containing at least one of Zn, Mg, Al, Pb, Ti, La, Zr, Bi, Si, or C, and a relatively readily available material is selected, such that allows to reduce the production costs for the moderator, with the implementation of a certain effect of slowing down neutrons and without a significant impact on the quality of the beam; wherein Teflon used for the second auxiliary block of the moderator can be replaced with graphite, etc., and material A with a better fast neutron absorption effect compared to the material of the first auxiliary block is selected for the second auxiliary block, which makes it possible to reduce the content of fast neutrons in bundle. It is contemplated that at least two of the first auxiliary block, the second auxiliary block, and the moderator base may alternatively be made from the same material.

As shown in FIG. 7 and FIG. 8, the support portion 21 is further provided with radial baffles 210, the plane in which the radial baffle 210 is located passes through the main axis X, and each of the enclosing blocks C1-C3 is circumferentially divided into at least two sub-regions, so that a block of PE, a lead block, an aluminum alloy block, and a graphite block disposed in each of the enclosing blocks C1-C3 are uniformly divided into at least two sub-modules along the circumference. In this embodiment, the first radial baffle 2101 is located between the first side plate 221 and the second side plate and extends from the outer wall 211 to the second inner wall 213; the second radial baffle 2102 is located between the first side plate 221 and the second transverse plate 224 and extends from the second inner wall 213 to the third inner wall 214 or the fourth inner wall 215. In this embodiment, there are eight first radial baffles and four second radial baffles, all evenly distributed around the circumference; the first radial baffles and the second radial baffles are flat plates, and every second radial baffle and four of the first radial baffles are in the same plane. It is contemplated that alternatively, there may be other numbers or designs of the radial baffle, or the radial baffle may not be used.

In this embodiment, the radial baffles 210, the outer wall 211, the first cross plate 223, and the first, second, third, and fourth inner walls 212-215 are integrally formed as the main frame 21a, and the material is an aluminum alloy with suitable mechanical properties. and short half-life of radioactive isotopes generated by aluminum alloy after neutron activation. A casting process may be used and the support mold is molded as a single unit. The mold is wood mold or aluminum mold, and the sand core can be red sand or resin sand. A specific process is a method commonly used in the industry. Since there are demoulding slopes in casting, according to the design and beam quality requirements, the demoulding slopes must be removed by machining. Due to this design and casting process, the frame structure has the advantages of good integrity, high rigidity and high load-bearing capacity. Due to the limitations of machining cutting tools and stress concentration on rectangular sides, all corners are rounded. Alternatively, the plate may be first rolled and welded or forged into an aluminum alloy cylinder, after which the cylinder is machined to form.

Fig. 9 shows an embodiment of the main frame during processing. In this embodiment, the main frame 21a is made of 6061 aluminum alloy, which can meet the chemical composition and mechanical properties of the main frame material. In order to meet the requirement of a short half-life of radioactive isotopes generated by the main body after activation by neutrons, it is necessary to control the types of aluminum alloy elements and the mass ratios of the elements. For example, the mass fraction of Cu is ≤7%. Based on relevant calculations and experience, the chemical composition of the main frame material selected in this embodiment is Cu≦1.0%, Mn≦1.5%, and Zn≦1.0% (mass percentage). The chemical composition of the 6061 aluminum alloy is shown in Table 1, and by comparison, it can be seen that the 6061 aluminum alloy can meet the chemical composition required for the material of the main frame 21a.

In order to support the main frame 21a on the main body 23 of the beam former, the mechanical properties of the main frame must meet these requirements. According to CAE simulation calculations and empirical adjustments, for the aluminum alloy main frame selected in this embodiment, the tensile strength is ≥150 MPa and the yield strength is ≥100 MPa.

Because 6061 aluminum alloy is a malleable aluminum alloy, this embodiment adopts an open-die forging method, the structure and properties of the aluminum alloy are changed using a plastic forming method, which saves raw materials. In free forging, the quality of forging largely depends on the structure of the metal obtained during deformation, especially on the uniformity of forging deformation. Non-uniform deformation reduces the ductility of the metal, and due to non-uniform recrystallization, a non-homogenized structure is obtained, so that forging properties deteriorate. In order to obtain a uniform deformed structure and optimal mechanical properties, the fewer procedures and the shorter heating periods, the better. The processing of this option is as follows:

1. Billet material preparation: manufacturers such as aluminum smelters process aluminum ore into aluminum ingots, cast aluminum ingots into a billet, prepare the billet material in the composition of 6061 aluminum alloy, which meets the national standard, and determine the billet material, such as data and experimental results on aspects such as alloy number, melting furnace, batch number, technical specifications, homogenization annealing, low temperature annealing, oxide film inspection.

2. Cutting. The workpiece material that meets certain requirements is processed by such methods as cutting, sawing and gas cutting. For example, end face cutting is performed, and burrs, oil stains, and sawdust are removed in time to meet the processing requirements of forging equipment.

3. Heating: The material blank is heated before forging to reduce deformation resistance and improve ductility. For example, a radiant resistive heating oven is used, air is circulated in the oven to maintain an accurate and uniform temperature, and the temperature deviation of the oven can be controlled within ±10°C. In this embodiment, the maximum forging start temperature is 520°C, the forging end temperature is 450°C, and the allowable limit temperature is 530°C. Of course, other heating equipment can be used as an alternative. When determining the heat retention time, it is necessary to fully take into account such factors as the thermal conductivity of the alloy, the characteristics of the material of the workpiece, the heat transfer modes of the heating equipment, etc. In this embodiment, the heating time is determined according to the dissolution of the strengthening phase and the homogenization of the structure. In this state, appropriate ductility can be obtained, and the forging performance of the aluminum alloy can be improved. It is contemplated that the workpiece material may alternatively be heated before cutting in step 2. In this case, before the workpiece material is heated, for example, before the workpiece material enters the heating furnace, oil stains, dust and other contaminants must be removed so as not to contaminate air in the oven.

4. Forging: 6061 aluminum alloy material is polycrystalline, there are grain boundaries between the grains, and there are subgrains and interfacial boundaries inside the grains. Thus, the material is plastically deformed based on the plasticity of the material using an external force to obtain a forging of the desired shape (eg cylinder), size and certain structural properties. The cast structure of the material of the metal blank is eliminated by forging deformation, which greatly improves the ductility and mechanical properties. In this embodiment, free forging method such as upsetting and drawing is used, provided that the forging temperature is not lower than the set temperature, static forging is repeated in accordance with the processes of the above two methods to obtain fine grains in the structure, the forging equipment has the accuracy of forging a workpiece.

5. Rough machining and heat treatment: In order to end up with mechanical properties that meet the requirements of use, it is also necessary to change the structure and properties of the metal material through heat treatment to change the internal quality of the metal. In this embodiment, the cylinder is obtained by forging in step 4. When the heat treatment is performed directly on the cylinder, it is difficult to obtain the desired material characteristics in the center of the cylinder. Thus, a hole is drilled in the center position (i.e., in the cylinder regions corresponding to the fourth containing block C4) of the forged cylinder by rough machining, then deep heat treatment is performed so that the support frame can be close to the center position (to form the main parts of the frame of the fourth containing block C4) and the general properties of the material after heat treatment. In addition, the fourth housing block C4 accommodates the base part of the moderator, which allows the maintenance of the moderator, and deformation and damage of the moderator is prevented, so as to avoid affecting the change of the target and the quality of the beam. It is understood that the rough machining further comprises pre-machining the hollow regions (that is, the cylinder regions corresponding to the first containing block C1, the second containing block C2, and the third containing block C3) between the outer wall 211 and the inner walls 212-215 of the main frame, for example, in these areas, the solid part of the cylinder obtained by forging is drilled and milled. In this embodiment, rough machining is not performed in these areas to prevent the areas from being easily deformed due to thinness during heat treatment after rough machining. In the event that the process can provide the desired material properties of the central region and other regions, rough machining may not be performed. Rough machining must leave an allowance for subsequent machining.

In this embodiment, T6 heat treatment (solid solution + aging) is used. Solution treatment is the preceding procedure for precipitation hardening of an alloy. The solid solution formed by solution processing is rapidly cooled to obtain a metastable supersaturated solid solution, which creates conditions for natural aging and artificial aging, and greatly improves strength and hardness. After solution treatment, aging treatment is required, while aluminum after solution treatment is kept at a certain temperature for a certain time, and the supersaturated solid solution decomposes, resulting in a significant increase in the strength and hardness of the alloy, and aluminum can be stored at room temperature or with heating. Aging treatment is the final heat treatment procedure that improves and defines the final mechanical properties of an aluminum alloy. The heating temperature and keep warm time can be selected according to the specific situation. It is contemplated that other heat treatment processes may alternatively be used, as long as the mechanical properties are consistent with the requirements of the use.

6. Physical and chemical testing and verification. After heat treatment, it is necessary to carry out physical and chemical testing and inspection, including dimensional inspection, element inspection, mechanical property testing, non-destructive ultrasonic flaw detection, etc. Testing may be carried out after heat treatment by appropriate heat treatment personnel, or verification may be carried out before machining by appropriate machining personnel (see below). Checking the mechanical properties can be done by cutting off a portion of the material in the appropriate area of the workpiece after heat treatment. In this embodiment, the part removed by drilling a hole at the center position can be heat treated by rough machining, and the part is tested to approximately obtain the properties of the inner walls 214 and 215 near the major X axis; the area between the outer wall 211 and the inner walls 212-215 is tested by cutting the forged cylinder material after heat treatment in this area. It is understood that when rough machining is performed on the hollow areas between the outer wall 211 and the inner walls 212-215, the part cut off when the area is rough machined is checked after heat treatment to approximately obtain the properties of the area, while the selected area can be marked on the drawing. The above area is selected for mechanical testing to obtain yield strength and tensile strength. In non-destructive testing, ultrasonic flaw detection is used, which can be a general inspection or a partial one. In this embodiment, ultrasonic testing is performed on the inner wall close to the center.

7. Machining: after testing and inspection, and if the forged body after heat treatment meets the requirements, machining is performed to obtain the main frame with the final required shape and size. It is contemplated that machining may include conventional machining methods such as drilling, milling, and turning. In this embodiment, a large gantry milling machine is used for milling and interacts with automated machining software.

The main frame 21a and the second cross plate 224 are bolted together. The first threaded hole is uniformly made on the end surface facing the second side plate 222 of the fourth inner wall 215. The first through hole is uniformly made in accordance with the first threaded hole on the second cross plate 224. The bolt passes through the first through hole and connects to the first threaded hole . Due to the assembly of the bolt, the hole diameter of the first through hole is slightly larger than the hole diameter of the first threaded hole, and the number of the first threaded holes and the first through holes should only correspond to the strength of the connection. The material of the first side plate 221, the second side plate 222 and the second cross plate 224 is lead antimony alloy. Lead can additionally shield the radiation, and in addition, the lead-antimony alloy has a relatively high strength. The outer contours of the first side plate 221 and the second side plate 222 correspond to the outer contour of the outer wall 211. The first side plate 221, the second side plate 222 and the second cross plate 224 are bolted to the main frame. The second threaded holes are uniformly made on the end surfaces facing the first side plate, the second side plate, and the second transverse plate of the inner wall of the main frame 21a, respectively. The second through holes are uniformly made at positions corresponding to the second threaded holes of the first side plate 221, the second side plate 222, and the second cross plate 224. Due to the bolt assembly, the diameter of the second through hole is slightly larger than the diameter of the second threaded hole, and the number of second threaded through holes should only correspond to the strength of the connection.

Of course, in this embodiment, the materials of the main frame, side plate and end plate (second cross plate) only need to have a certain strength and a short half-life of radioactive isotopes generated by the materials after neutron activation (for example, less than 7 days), and the material properties of the main Frames can meet the requirements of maintaining a beam forming device, such as aluminum alloy, titanium alloy, lead-antimony alloy, cobalt-free steel, carbon fiber, PEEK or high polymer. Other detachable connections or detachable connections may be provided between the side plate, the end plate (second cross plate) and the main frame. When a detachable connection is used, it is convenient to replace each part of the main body. In this embodiment, the support part and the main part filled inside the support part of the beam forming unit may alternatively have a different design.

During construction, the main frame 21a is first inserted into the mounting hole contained in the support portion of the beam forming unit, the outer wall 211 of the main frame 21a and the supporting part of the beam forming unit are bolted together. Then the filling of the main body and mounting of the first side plate, the second side plate and the second cross plate is carried out. Due to the low density of PE, aluminum alloy and graphite, the respective areas can be completely filled. Because lead is relatively heavy, lead can be filled by hand in portions in the direction of the neutron beam N, or it can be completely filled by machine. Magnesium fluoride can also be filled in whole or in parts. After mounting the beam forming unit, the transmitting tube, target, collimator and other components are mounted. The collimator 30 is located at the rear of the beam exit. The epithermal neutron beam from the collimator 30 is irradiated to the patient 200 and moderated to thermal neutrons after passing through the superficial normal tissues to reach the tumor cell M. side plate, the second inner wall 213, and the third through hole are uniformly made at the position corresponding to the third threaded hole of the second side plate 222. Due to the assembly of the bolt, the hole diameter of the third through hole is slightly larger than the hole diameter of the third threaded hole, and the number of third threaded holes and third through holes should only correspond to the strength of the connection. It is contemplated that the collimator 30 may alternatively be secured by other means, the collimator 30 may alternatively be removed or replaced by another structure, and the neutron beam from the beam exit directly irradiates the patient 200. In this embodiment, the radiation shielding device 50 is further placed between the patient 200 and the beam exit to shield the normal tissue of the irradiated subject from beam irradiation from the beam exit. It should be understood that the radiation shielding device 50 cannot be removed.

The term "cylindrical" or "cylindrical section" as used in describing an embodiment of the present invention refers to an element whose contour extends substantially from one side to the other along the illustrated direction. One of the contour lines may be a line segment, like the corresponding cylinder segment, or may be a high curvature arc close to a line segment, like the corresponding high curvature sphere arc. The integral surface of the contour may or may not be continuously connected if the surface of a highly curvature cylinder or sphere has a plurality of protrusions and grooves.

The term "tapered" or "tapered section" as used in describing an embodiment of the present invention refers to an element whose contour tends to taper from one side to the other along the illustrated direction. One of the contour lines may be a straight line segment, like that of a cone, or may be an arc, like that of a sphere, and the integral surface of the contour may or may not be continuously connected if the cone-shaped or spherical-shaped surface is provided with a plurality of protrusions and grooves.

While exemplary embodiments of the present invention have been described above to enable one skilled in the art to understand the invention, it should be understood that the invention is not limited to the disclosed embodiments. For those skilled in the art, as long as the changes are within the spirit of the invention and the scope of legal protection defined by the appended claims, any changes will be obvious and within the legal claims of the present invention.

Claims (14)

1. A neutron capture therapy system containing a neutron generation device and a beam formation unit, while the neutron generation device contains an accelerator and a target, a beam of charged particles generated during acceleration of the accelerator interacts with the target to generate neutrons, neutrons form a neutron beam passing along the main axis, the beam forming unit contains a support part and a main part filled inside the support part, the main part contains a moderator, a reflector and a radiation shield, and the moderator is configured to slow down neutrons generated from the target to the epithermal neutron energy range, the reflector surrounds the moderator and directs deviating neutrons back to the main axis to increase the intensity of the epithermal neutron beam and the radiation shield is designed to shield leaking neutrons and photons to reduce the dose for normal tissues in the non-irradiated zone, while the supporting part contains an outer wall , closed in a circle around the main axis, the outer wall, surrounding, forms a containing part, the main part is located in the containing part, the containing part contains at least one containing block, and each containing block contains at least one of the moderator, reflector and radiation screen . 2. The neutron capture therapy system according to claim 1, in which the supporting part further comprises a first side plate and a second side plate located respectively on both sides of the outer wall in the direction of the neutron beam and connected to the outer wall, at least one transverse plate, located between the first side plate and the second side plate in the direction of the neutron beam, and at least one inner wall, closed in a circle around the main axis and passing between the first side plate and the second side plate, or between the transverse plate and the first side plate, or between transverse plate and the second side plate, or between the transverse plates, in the first side plate there is a hole for passing the accelerator transfer tube, in the second side plate there is a hole for forming the beam exit, there are enclosing blocks formed between the outer wall, the inner wall, the transverse plate mud, the first side plate and the second side plate, the radiation shield contains a neutron shield and a photon shield, and at least one enclosing block accommodates both the moderator and the reflector, or both the neutron shield and the reflector. 3. The neutron capture therapy system according to claim 2, wherein the neutron shield material is polyethylene (PE), the reflector material is lead, the reflector is additionally made as a photonic shield, the reflector and the neutron shield, both placed in the containing unit, are sequentially located in direction of the neutron beam and the boundary between the reflector and the neutron screen in the enclosing block is perpendicular to the direction of the neutron beam. 4. The neutron capture therapy system according to claim 2, in which the supporting part further comprises radial partitions, circumferentially separating the enclosing block into sub-regions, the radial partitions are located between the first side plate and the second side plate, or between the transverse plate and the first/second side plate. plate, or between transverse plates, and extends from an outer wall to an inner wall, or extends between two inner walls. 5. The neutron capture therapy system according to claim 1, in which the moderator comprises a base part and an auxiliary part surrounding the base part, the support part contains a wall around the main axis, while the base part and the auxiliary part are made of different materials and are separated by a wall. 6. The neutron capture therapy system according to claim 5, in which the wall comprises a first wall, a second wall and a transverse plate connecting the first wall and the second wall, which are sequentially located in the direction of the neutron beam and are closed in a circle around the direction of the neutron beam, the transverse plate passes perpendicular to the direction of the neutron beam, the first wall is intended for mounting the transfer tube of the accelerator, the second wall forms a containing cavity for the base part of the moderator, the material of the base part contains at least one of D ₂ O, Al, AlF ₃ , MgF ₂ , CaF ₂ , LiF , Li ₂ CO ₃ or Al ₂ O ₃ and the base part contains Li-6, while the base part is also made as a thermal neutron absorber. 7. The neutron capture therapy system according to claim 6, in which the base part contains the first end surface and the second end surface, which are perpendicular to the direction of the neutron beam, the first end surface and the second end surface are located sequentially in the direction of the neutron beam, the first end surface is provided with a central hole, and the central hole is designed to accommodate the transmission tube and the target, and the radial distance from the first wall to the main axis is less than the radial distance from the second wall to the main axis. 8. The neutron capture therapy system of claim 7, wherein a shielding plate is provided proximate the second end surface, wherein the shielding plate is a lead plate and the thickness of the shielding plate in the direction of the neutron beam is less than or equal to 5 cm. 9. The neutron capture therapy system according to claim 5, in which the auxiliary part contains the first auxiliary block and the second auxiliary block located next to each other, while the base part, the first auxiliary block and the second auxiliary block are made of three different materials, the base the part is cylindrical, and the first auxiliary block and the second auxiliary block are integrally formed into a shape having at least one conical shape. 10. The neutron capture therapy system according to claim 9, in which the first auxiliary block is made in the form of two cone-shaped forms located next to each other in opposite directions, while the first auxiliary block contains a first cone-shaped section and a second cone-shaped section, successively located in the direction of the neutron beam, the radial size of the outer contour of the first cone-shaped section gradually increases in the direction of the neutron beam as a whole, the second cone-shaped section is connected to the first cone-shaped section in a position where the radial size of the outer contour of the first cone-shaped section is maximum, while the radial size of the outer contour of the second cone-shaped section gradually decreases in the direction of the neutron beam as a whole, the second auxiliary block is located next to the second cone section in a position where the radial size of the outer contour of the second cone section is minimal, and the radial size of the outer contour the second auxiliary block gradually decreases in the direction of the neutron beam as a whole. 11. The neutron capture therapy system according to claim 10, wherein the cross-sectional contours of the first auxiliary block and the second auxiliary block in the plane where the main axis is located are irregular quadrilaterals or polygons, and the first auxiliary block contains the first side in contact with the reflector on the first cone-shaped section, the second side in contact with the reflector, and the third side in contact with the second auxiliary block on the second cone-shaped section, and the fourth side in contact with the wall on both the first cone-shaped section and the second cone-shaped section, the second auxiliary block contains the fifth side, contact with the first auxiliary block, the sixth side in contact with the reflector, and the seventh side in contact with the wall, the third side and the fifth side are located side by side and are made as a boundary between the first auxiliary block and the second auxiliary block, and the boundary is perpendicular cular to the direction of the neutron beam. 12. The neutron capture therapy system according to claim 1, wherein the support portion comprises a support frame, the support frame is formed by heating a workpiece of material with a heating equipment, and then forging into a cylinder with a forging equipment, the cylinder being machined after rough machining and heat treatment. 13. The neutron capture therapy system according to claim 12, wherein the support frame forms at least one containing block, wherein the containing block comprises a first containing block containing at least a portion of the moderator, the first containing block is located in the center of the support frame in the radial direction , and rough machining is the drilling of holes in the areas of the cylinder corresponding to the first enclosing block. 14. The neutron capture therapy system according to claim 13, in which the accommodating block comprises a second accommodating block containing at least one of the moderator, reflector and radiation shield, the support frame contains an outer wall, closed in a circle around the main axis, and at least at least one inner wall, the second containing block is formed between the outer wall and the inner wall or between the inner walls, and the rough machining further comprises pre-machining the cylinder regions corresponding to the second containing block.

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