CN204319539U - For the beam-shaping body of neutron capture treatment - Google Patents

Abstract

In order to improve the flux and quality of the neutron radiation source, one aspect of the present invention provides a beam shaping body for neutron capture therapy, wherein the beam shaping body includes a beam entrance, a target material, and a beam shaper adjacent to the target The retarder of the material, the reflector surrounded by the retarder, the thermal neutron absorber adjacent to the retarder, the radiation shield and the beam exit arranged in the beam shaping body, the target material and the incident radiation from the beam entrance The proton beam undergoes a nuclear reaction to produce neutrons, and the neutrons form a neutron beam. The neutron beam defines a main axis, and the retarder decelerates the neutrons generated from the target to the epithermal neutron energy region. The retarder is set Into a shape containing at least one cone, the reflector guides off-axis neutrons back to the main axis to increase the intensity of the epithermal neutron beam, and the thermal neutron absorber is used to absorb thermal neutrons to avoid treatment with shallow normal Excessive dose to tissue, radiation shielding is used to shield neutrons and photons from leakage to reduce normal tissue dose in non-irradiated areas.

Description

Beam Shapers for Neutron Capture Therapy

technical field

The utility model relates to a beam shaping body, in particular to a beam shaping body for neutron capture therapy.

Background technique

With the development of atomic science, radiation therapy such as cobalt 60, linear accelerator, and electron beam has become one of the main means of cancer treatment. However, traditional photon or electron therapy is limited by the physical conditions of the radiation itself. While killing tumor cells, it will also cause damage to a large number of normal tissues along the beam path; in addition, due to the different sensitivity of tumor cells to radiation, traditional radiation therapy Treatment for more radiation-resistant malignancies (eg, glioblastoma multiforme, melanoma) is often less effective.

In order to reduce radiation damage to normal tissues around the tumor, the concept of target therapy in chemotherapy (chemotherapy) has been applied to radiation therapy; and for tumor cells with high radiation resistance, it is also actively developing tumor cells with high relative biological effects (relative biological effects). Biological effectiveness (RBE) radiation sources, such as proton therapy, heavy particle therapy, neutron capture therapy, etc. Among them, neutron capture therapy is a combination of the above two concepts, such as boron neutron capture therapy, through the specific accumulation of boron-containing drugs in tumor cells, combined with precise neutron beam regulation, it provides better treatment than traditional radiation. Cancer treatment options.

Boron Neutron Capture Therapy (BNCT) utilizes boron-containing ( ¹⁰ B) drugs that have a high capture cross-section for thermal neutrons, through ¹⁰ B(n,α) ⁷ Li neutron capture and nuclear fission reaction Produce ⁴ He and ⁷ Li two heavily charged particles. Referring to Figure 1 and Figure 2, they respectively show the schematic diagram of the boron neutron capture reaction and ^{the 10} B(n,α) ⁷ Li neutron capture nuclear reaction equation, the average energy of the two charged particles is about 2.33MeV, with high linearity Transfer (Linear Energy Transfer, LET), short-range characteristics, the linear energy transfer and range of α particles are 150keV/μm, 8μm, respectively, and ⁷ Li heavy particles are 175keV/μm, 5μm, the total range of the two particles is about equivalent to The size of a cell, so the radiation damage to the organism can be limited to the cell level. When the boron-containing drug is selectively accumulated in the tumor cells, with an appropriate neutron radiation source, it can not cause too much damage to normal tissues. Under the premise, the purpose of locally killing tumor cells is achieved.

Because the effectiveness of boron neutron capture therapy depends on the concentration of boron-containing drugs and the number of thermal neutrons in the tumor cells, it is also called binary cancer therapy; it can be seen that in addition to the development of boron-containing drugs, The improvement of neutron radiation source flux and quality plays an important role in the research of boron neutron capture therapy.

Utility model content

In order to improve the flux and quality of the neutron radiation source, one aspect of the present invention provides a beam shaping body for neutron capture therapy, wherein the beam shaping body includes a beam entrance, a target material, and a beam shaper adjacent to the target The retarder of the material, the reflector surrounded by the retarder, the thermal neutron absorber adjacent to the retarder, the radiation shield and the beam exit arranged in the beam shaping body, the target and the incident beam entrance The proton beam undergoes a nuclear reaction to produce neutrons, the neutrons form a neutron beam, the neutron beam defines a main axis, the retarder decelerates the neutrons generated from the target to the epithermal neutron energy region, and the retarder Arranged to contain at least one cone-like shape, the reflector guides off-axis neutrons back to the main axis to increase the intensity of the epithermal neutron beam, and the thermal neutron absorber is used to absorb thermal neutrons to avoid contact with shallow layers during treatment Normal tissue causes excessive dose, and radiation shielding is used to shield the leaking neutrons and photons to reduce the normal tissue dose in the non-irradiated area.

The beam shaper is further used in accelerator boron neutron capture therapy.

Accelerator boron neutron capture therapy accelerates the proton beam through the accelerator, the target is made of metal, the proton beam is accelerated to an energy sufficient to overcome the Coulomb repulsion of the target nucleus, and undergoes a nuclear reaction with the target to generate neutrons.

The beam shaping body can slow neutrons to the epithermal neutron energy region, and reduce the content of thermal neutrons and fast neutrons. The epithermal neutron energy region is between 0.5eV and 40keV, and the thermal neutron energy region is less than 0.5eV , the fast neutron energy range is greater than 40keV, the retarder is made of materials with large cross-section for fast neutrons and small cross-section for epithermal neutrons, the reflector is made of materials with strong neutron reflection ability, thermal neutrons The absorber is made of a material with a large cross section for thermal neutrons.

As a preference, the retarder is made of at least one of D ₂ O, AlF ₃ , Fluental ^TM , CaF ₂ , Li ₂ CO ₃ , MgF ₂ and Al ₂ O ₃ .

Further, the reflector is made of at least one of Pb or Ni, the thermal neutron absorber is made of ⁶ Li, and an air channel is provided between the thermal neutron absorber and the beam exit.

Radiation shielding includes photon shielding and neutron shielding. As a preference, the photon shield is made of Pb, and the neutron shield is made of PE (polyethylene).

As a preference, the slowing body is arranged in a shape including a cylinder and a cone adjacent to the cylinder, or is arranged in two cones adjacent to each other in opposite directions.

The "column" or "cylindrical shape" mentioned in the embodiments of the present utility model refers to a structure whose overall trend of the outer contour is basically unchanged from one side to the other side along the direction shown in the figure, and one of the outer contours The contour line can be a line segment, such as the corresponding contour line of a cylinder, or a circular arc close to the line segment with a large curvature, such as a corresponding contour line of a spherical body with a large curvature. The entire surface of the outer contour can be A smooth transition can also be a non-smooth transition, such as making a lot of protrusions and grooves on the surface of a cylinder or a spherical body with a large curvature.

The "cone" or "cone-shaped" mentioned in the embodiment of the utility model refers to a structure whose overall trend of the outer contour gradually becomes smaller along the direction shown in the figure from one side to the other side, one of the outer contours The contour line can be a line segment, such as a cone-shaped corresponding contour line, or a circular arc, such as a spherical body-shaped corresponding contour line. The entire surface of the outer contour can be a smooth transition or a non-smooth transition. For example, many protrusions and grooves are made on the surface of a cone or a sphere.

Description of drawings

Figure 1 is a schematic diagram of boron neutron capture reaction.

Figure 2 is ^{the 10} B(n,α) ⁷ Li neutron capture nuclear reaction equation.

Fig. 3 is a schematic plan view of the beam shaper for neutron capture therapy in the first embodiment of the present invention, wherein a gap channel is provided between the retarder and the reflector.

Fig. 4 is a schematic plan view of the beam shaping body used for neutron capture therapy in the second embodiment of the present invention, wherein the slowing body is arranged as a double cone, and the position of the gap channel in the first embodiment is slowed down. Velocity material filling.

Fig. 5 is a schematic plan view of the beam shaping body for neutron capture therapy in the third embodiment of the present invention, wherein the slowing body is arranged as a double cone, and the position of the gap channel in the first embodiment is based on the reflection body material filling.

Fig. 6 is a neutron yield diagram of neutron energy and neutron angle double differential.

Fig. 7 is a schematic plan view of the beam shaper for neutron capture therapy in the fourth embodiment of the present invention, wherein the retarder is arranged as a cylinder.

Fig. 8 is a schematic plan view of the beam shaper for neutron capture therapy in the fifth embodiment of the present invention, wherein the retarder is arranged as a cylinder + a cone.

Detailed ways

The application of neutron capture therapy as an effective means of treating cancer has gradually increased in recent years, among which boron neutron capture therapy is the most common, and neutrons supplying boron neutron capture therapy can be supplied by nuclear reactors or accelerators. The embodiment of the present utility model takes the accelerator boron neutron capture therapy as an example. The basic components of the accelerator boron neutron capture therapy usually include an accelerator, a target material and a heat transfer device for accelerating charged particles (such as protons, deuterons, etc.). In addition to the system and the beam shaper, in which the accelerated charged particles interact with the metal target to generate neutrons, according to the required neutron yield and energy, the available accelerated charged particle energy and current, the physical and chemical properties of the metal target, etc. The nuclear reactions that are often discussed are ⁷ Li(p,n) ⁷ Be and ⁹ Be(p,n) ⁹ B, both of which are endothermic reactions. The energy thresholds of the two nuclear reactions are 1.881MeV and 2.055MeV respectively. Since the ideal neutron source for boron neutron capture therapy is epithermal neutrons at the energy level of keV, in theory, if proton bombardment with energy only slightly higher than the threshold is used Lithium metal targets can produce relatively low-energy neutrons, and can be used clinically without too much retardation treatment. Not high, in order to generate enough neutron flux, usually choose higher energy protons to initiate nuclear reactions.

An ideal target should have the characteristics of high neutron yield, neutron energy distribution close to the epithermal neutron energy region (described in detail below), no strong penetrating radiation, safe, cheap, easy to operate, and high temperature resistance. But in fact, it is impossible to find a nuclear reaction that meets all the requirements. In the embodiment of the present invention, a target made of lithium metal is used. However, those skilled in the art are well aware that the material of the target can also be made of other metal materials besides the metal materials mentioned above.

The requirements for the heat removal system vary according to the selected nuclear reaction. For example, ⁷ Li(p,n) ⁷ Be has lower requirements for the heat removal system due to the poor melting point and thermal conductivity of the metal target (lithium metal). ⁹ Be(p,n) ⁹ B high. In the embodiment of the present utility model, the nuclear reaction of ⁷ Li(p,n) ⁷ Be is adopted.

Regardless of whether the neutron source of boron neutron capture therapy comes from a nuclear reactor or the nuclear reaction between charged particles and the target in an accelerator, the resulting radiation field is a mixed radiation field, that is, the beam contains low-energy to high-energy neutrons and photons; In electron capture therapy, except for epithermal neutrons, the more radiation content, the greater the proportion of non-selective dose deposition in normal tissues, so these radiations that cause unnecessary doses should be reduced as much as possible. In addition to the air beam quality factor, in order to better understand the dose distribution caused by neutrons in the human body, in the embodiments of the present invention, the human head tissue prosthesis is used for dose calculation, and the prosthesis beam quality factor is used as the neutron dose distribution. The beam design reference will be described in detail below.

The International Atomic Energy Agency (IAEA) has given five recommendations for air beam quality factors for neutron sources used in clinical boron neutron capture therapy. These five recommendations can be used to compare the pros and cons of different neutron sources and serve as The reference basis for selecting the neutron generation path and designing the beam shaper. The five recommendations are as follows:

Epithermal neutron flux>1x 10 ⁹ n/cm ² s

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

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

thermal to epithermal neutron flux ratio<0.05

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

Note: The epithermal neutron energy range is between 0.5eV and 40keV, the thermal neutron energy range is less than 0.5eV, and the fast neutron energy range is greater than 40keV.

1. Epithermal neutron beam flux:

The neutron beam flux and the concentration of boron-containing drugs in the tumor jointly determine the clinical treatment time. If the concentration of boron-containing drugs in the tumor is high enough, the requirement for neutron beam flux can be reduced; on the contrary, if the concentration of boron-containing drugs in the tumor is low, high-flux epithermal neutrons are required to deliver sufficient doses to the tumor. The IAEA's requirement for the flux of epithermal neutron beams is that the number of epithermal neutrons per second per square centimeter is greater than 10 ⁹ , neutron beams under this flux can roughly control the treatment for current boron-containing drugs The time is less than one hour. In addition to the advantages of patient positioning and comfort, the short treatment time can also make more effective use of the limited residence time of boron-containing drugs in the tumor.

2. Fast neutron pollution:

Because fast neutrons will cause unnecessary normal tissue dose, it is regarded as pollution. The dose size is positively correlated with neutron energy, so the content of fast neutrons should be minimized in neutron beam design. Fast neutron pollution is defined as the fast neutron dose accompanied by unit epithermal neutron flux, and the IAEA's suggestion for fast neutron pollution is less than 2x 10 ^-13 Gy-cm ² /n.

3. Photon pollution (gamma ray pollution):

γ-rays are strong penetrating radiation, which will non-selectively cause dose deposition in all tissues on the beam path, so reducing the content of γ-rays is also a necessary requirement for neutron beam design. γ-ray pollution is defined as unit epithermal neutron flux accompanied by The gamma-ray dose, the IAEA's suggestion for gamma-ray pollution is less than 2x 10 ^-13 Gy-cm ² /n.

4. The flux ratio of thermal neutrons and epithermal neutrons:

Due to the fast attenuation speed and poor penetration ability of thermal neutrons, most of the energy is deposited in skin tissue after entering the human body. For tumors and other deep tumors, the content of thermal neutrons should be reduced. The IAEA recommends that the flux ratio of thermal neutrons to epithermal neutrons be less than 0.05.

5. The ratio of neutron current to flux:

The ratio of neutron current to flux represents the directionality of the beam. The larger the ratio, the better the forwardness of the neutron beam. The neutron beam with high forwardness can reduce the dose to surrounding normal tissues caused by neutron divergence. It also improves the depth of treatment and the flexibility of positioning. The IAEA recommends that the neutron current-to-flux ratio be greater than 0.7.

The dose distribution in the tissue is obtained by using the prosthesis, and the beam quality factor of the prosthesis is deduced according to the dose-depth curve of normal tissue and tumor. The following three parameters can be used to compare the 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 this depth, the dose received by tumor cells is less than the maximum dose of normal tissue, that is, the advantage of boron neutron capture is lost. This parameter represents the penetrating ability of the neutron beam. The greater the effective treatment depth, the deeper the tumor can be treated. The unit is cm.

2. Effective treatment depth dose rate:

That is, the effective treatment depth of tumor dose rate is equal to the maximum dose rate of normal tissue. Since the total dose received by normal tissues is a factor that affects the total dose that can be given to the tumor, the parameters affect the length of treatment time. The greater the effective treatment depth dose rate, the shorter the irradiation time required to give a certain dose to the tumor. The unit is cGy/mA -min.

3. Effective therapeutic dose ratio:

From the surface of the brain to the effective treatment depth, the average dose ratio received by the tumor and normal tissue is called the effective treatment dose ratio; the calculation of the average dose can be obtained 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 design of the beam shaping body have a comparative basis, in addition to the five IAEA-recommended beam quality factors in the air and the above three parameters, the following method for evaluating the neutron beam dose is also used in the embodiment of the present invention Performance parameters:

1. Irradiation time ≤ 30min (the proton current used by the accelerator is 10mA)

2. 30.0RBE-Gy can treat depth ≥ 7cm

3. The maximum tumor dose ≥ 60.0RBE-Gy

4. The maximum dose of normal brain tissue is ≤12.5RBE-Gy

5. The maximum skin dose ≤ 11.0RBE-Gy

Note: RBE (Relative Biological Effectiveness) is a relative biological effect. Since the biological effects caused by photons and neutrons are different, the above dose items are multiplied by the relative biological effects of different tissues to obtain the equivalent dose.

In order to improve the flux and quality of the neutron radiation source, the embodiment of the present invention is an improvement proposed for the beam shaper used for neutron capture therapy, as a preferred method, it is aimed at the boron neutron capture used in the accelerator Improvements in the treatment of beam-shaping bodies. As shown in Figure 3, the beam shaper 10 for neutron capture therapy in the first embodiment of the present utility model includes a beam entrance 11, a target 12, a slowing body 13 adjacent to the target 12, Surrounding the reflector 14 outside the slowing body 13, the thermal neutron absorber 15 adjacent to the slowing body 13, the radiation shielding 16 and the beam outlet 17 arranged in the beam shaping body 10, the target 12 and the self-radiating The proton beam entering the beam entrance 11 undergoes a nuclear reaction to generate neutrons, and the neutrons form a neutron beam, and the neutron beam defines a main axis X, and the retarder 13 decelerates the neutrons generated from the target 12 into the superheat In the sub-energy region, the reflector 14 guides neutrons deviated from the main axis X back to the main axis X to increase the intensity of the epithermal neutron beam, and a gap channel 18 is set between the retarder 13 and the reflector 14 to increase the epithermal neutron flux The thermal neutron absorber 15 is used to absorb thermal neutrons to avoid excessive doses to shallow normal tissues during treatment, and the radiation shield 16 is used to shield leaked neutrons and photons to reduce normal tissue doses in non-irradiated areas.

Accelerator boron neutron capture therapy accelerates the proton beam through the accelerator. As a preferred embodiment, the target 12 is made of lithium metal. The proton beam is accelerated to an energy sufficient to overcome the Coulomb repulsion of the target nucleus, and ⁷ Li (p,n) ⁷ Be nuclear reaction to produce neutrons. The beam shaper 10 can retard neutrons to the epithermal neutron energy region, and reduce the content of thermal neutrons and fast neutrons. The retarder 13 has a large cross-section for fast neutrons and a small cross-section for epithermal neutrons. As a preferred embodiment, the retarder 13 is made of at least one of D ₂ O, AlF ₃ , Fluental ^TM , CaF ₂ , Li ₂ CO ₃ , MgF ₂ and Al ₂ O ₃ . The reflector 14 is made of a material with strong neutron reflection capability. As a preferred embodiment, the reflector 14 is made of at least one of Pb or Ni. The thermal neutron absorber 15 is made of a material with a large cross-section with thermal neutrons. As a preferred embodiment, the thermal neutron absorber 15 is made of ⁶ Li, and the thermal neutron absorber 15 and the beam outlet 17 There are air passages 19 between them. The radiation shield 16 includes a photon shield 161 and a neutron shield 162. As a preferred embodiment, the radiation shield 16 includes a photon shield 161 made of lead (Pb) and a neutron shield 162 made of polyethylene (PE).

Wherein, speed-retarding body 13 is arranged as two conical shapes adjacent to each other in opposite directions. The right side is a cone shape that gradually becomes smaller toward the right, and the two are adjacent to each other. As a preference, the left side of the slowing body 13 is set in a cone shape that gradually becomes smaller toward the left side, and the right side can also be set in other shapes adjacent to the cone shape, such as a column shape. The reflector 14 is tightly surrounded around the slowing body 13, and a gap channel 18 is arranged between the slowing body 13 and the reflector 14. The so-called gap channel 18 refers to an empty space that is not covered by a solid material and is easy to let neutrons The region through which the beam passes, such as the gap channel 18, can be configured as an air channel or a vacuum channel. The thermal neutron absorber 15 arranged next to the retarder 13 is made of a very thin layer of ⁶ Li material, and the photon shield 161 made of Pb in the radiation shield 16 can be integrated with the reflector 14, or can be set components, and a neutron shield 162 made of PE in the radiation shield 16 may be disposed adjacent to the beam exit 17 . An air channel 19 is provided between the thermal neutron absorber 15 and the beam outlet 17, and in this area, the neutrons deviated from the main axis X can be continuously guided back to the main axis X to increase the intensity of the epithermal neutron beam. The prosthesis B is placed approximately 1 cm from the beam exit 17 . As is well known to those skilled in the art, the photon shield 161 can be made of other materials as long as it plays a role in shielding photons. The condition of leaking neutrons will do.

In order to compare the difference between the beam shaper with the gap channel and the beam shaper without the gap channel, as shown in Figure 4 and Figure 5, they respectively show the second implementation of filling the gap channel with retarder Example and a third embodiment of filling the interstitial channels with reflectors. Referring to Fig. 4 at first, this beam shaper 20 comprises beam entrance 21, target material 22, the retarder 23 that is adjacent to target material 22, the reflector 24 that surrounds retarder 23 outside, is adjacent to retarder 23. The thermal neutron absorber 25, the radiation shield 26 and the beam outlet 27 arranged in the beam shaping body 20, the target material 22 and the proton beam incident from the beam inlet 21 undergo a nuclear reaction to generate neutrons, and the neutrons form The sub-beam, the neutron beam defines a main axis X1, the retarder 23 decelerates the neutrons generated from the target 22 to the epithermal neutron energy region, and the reflector 24 guides the neutrons deviated from the main axis X1 back to the main axis X1 To improve the intensity of the epithermal neutron beam, the retarder 23 is arranged into two conical shapes adjacent to each other in opposite directions. The right side of the body is in the shape of a cone that gradually becomes smaller toward the right side, and the two are adjacent to each other. The thermal neutron absorber 25 is used to absorb thermal neutrons to avoid causing excessive doses with shallow normal tissues during treatment. The radiation shielding body 26 is used It is used to shield the leaking neutrons and photons to reduce the normal tissue dose in the non-irradiated area.

As a preference, the target 22, retarder 23, reflector 24, thermal neutron absorber 25 and radiation shield 26 in the second embodiment can be the same as those in the first embodiment, and the radiation shield therein 26 includes a photon shield 261 made of lead (Pb) and a neutron shield 262 made of polyethylene (PE), which may be provided at the beam exit 27 . An air channel 28 is arranged between the thermal neutron absorber 25 and the beam outlet 27 . The prosthesis B1 is placed approximately 1 cm from the beam exit 27 .

Please refer to Fig. 5, this beam shaper 30 comprises beam entrance 31, target material 32, the slow-down body 33 that is adjacent to target material 32, the reflector 34 that surrounds slow-speed body 33 outside, is adjacent to slow-down body 33 The thermal neutron absorber 35, the radiation shield 36 and the beam outlet 37 arranged in the beam shaping body 30, the target material 32 and the proton beam incident from the beam inlet 31 undergo a nuclear reaction to generate neutrons, and the neutrons form The sub-beam, the neutron beam defines a main axis X2, the retarder 33 decelerates the neutrons generated from the target 32 to the epithermal neutron energy region, and the reflector 34 guides the neutrons deviated from the main axis X2 back to the main axis X2 To improve the intensity of the epithermal neutron beam, the slowing body 33 is arranged into two conical shapes adjacent to each other in opposite directions, and the left side of the slowing body 33 is a tapered shape gradually decreasing towards the left side, and the slowing body 33 The right side of the body is in the shape of a cone that gradually becomes smaller toward the right side, and the two are adjacent to each other. The thermal neutron absorber 35 is used to absorb thermal neutrons to avoid causing excessive doses with shallow normal tissues during treatment. The radiation shielding body 36 is used for It is used to shield the leaking neutrons and photons to reduce the normal tissue dose in the non-irradiated area.

As a preference, the target 32, retarder 33, reflector 34, thermal neutron absorber 35 and radiation shield 36 in the third embodiment can be the same as those in the first embodiment, and the radiation shield therein 36 includes a photon shield 361 made of lead (Pb) and a neutron shield 362 made of polyethylene (PE), which may be provided at the beam exit 37 . An air channel 38 is arranged between the thermal neutron absorber 35 and the beam outlet 37 . The prosthesis B2 is placed approximately 1 cm from the beam exit 37 .

The MCNP software (which is developed by Los Alamos National Laboratory (Los Alamos National Laboratory) based on the Monte Carlo method) is used to calculate neutrons, photons, charged particles or coupled neutrons/photons in three-dimensional complex geometric structures. / The general software package of charged particle transport problem) to the simulation calculation of these three kinds of embodiments:

Wherein, the following table 1 shows the performance of the beam quality factor in the air in these three embodiments (the units of each noun in the table are the same as above, and will not be repeated here, the same below):

Table 1: Beam Quality Factors in Air

Wherein, the following table two shows the performance of dosage performance in these three kinds of embodiments:

Table 2: Dose performance

dose performance Accelerated mass fills interstitial channels Reflector fills gap channel Clearance channel effective treatment depth 10.9 10.9 11.0 effective treatment depth dose rate 4.47 4.60 4.78 Effective therapeutic dose ratio 5.66 5.69 5.68

Wherein, the following table three shows the simulated values of the parameters for evaluating the performance of the neutron beam dose in these three embodiments:

Table 3: Parameters for evaluating neutron beam dose performance

Note: From the above three tables, it can be known that the beam shaping body with a gap channel between the slowing body and the reflector has the best treatment benefit of the sub-beam.

Because the neutrons generated from the lithium target have the characteristics of high forward average energy, as shown in Figure 6, the average neutron energy of the neutron scattering angle between 0°-30° is about 478keV, and the neutron scattering angle The average neutron energy at an angle between 30°-180° is only about 290keV. If the geometry of the beam shaper can be changed, the forward neutrons will collide more with the retarder, while the neutrons in the side direction If the neutrons can reach the beam exit after fewer collisions, the neutron slowing speed should be optimized theoretically, and the epithermal neutron flux can be effectively improved. Starting from the geometric shape of the beam shaper, the influence of different geometric shapes of the beam shaper on the epithermal neutron flux is evaluated.

As shown in FIG. 7 , it shows the geometry of the beam shaper 40 in the fourth embodiment. The beam shaper 40 includes a beam entrance 41, a target 42, and a retarder 43 adjacent to the target 42. , a reflector 44 surrounded by the slowing body 43, a thermal neutron absorber 45 adjacent to the slowing body 43, a radiation shield 46 and a beam outlet 47 arranged in the beam shaping body 40, the target 42 and the self The incident proton beam at the beam entrance 41 undergoes a nuclear reaction to generate neutrons, the retarder 43 decelerates the neutrons generated from the target 42 to the epithermal neutron energy region, and the reflector 44 guides the deflected neutrons back to increase the neutron energy. The intensity of the thermal neutron beam, the retarder 43 is arranged in a cylindrical shape, preferably, it is arranged in a cylindrical shape, and the thermal neutron absorber 45 is used for absorbing thermal neutrons to avoid excessive contact with shallow normal tissues during treatment. Dose, the radiation shield 46 is used to shield the leaked neutrons and photons to reduce the normal tissue dose in the non-irradiated area, and an air channel 48 is provided between the thermal neutron absorber 45 and the beam outlet 47 .

As shown in FIG. 8 , it shows the geometry of the beam shaper 50 in the fifth embodiment, the beam shaper 50 includes a beam entrance 51 , a target 52 , and a retarder 53 adjacent to the target 52 , the reflector 54 surrounded by the retarder 53, the thermal neutron absorber 55 adjacent to the retarder 53, the radiation shield 56 and the beam outlet 57 arranged in the beam shaping body 50, the target 52 and the self The proton beam incident on the beam entrance 51 undergoes a nuclear reaction to generate neutrons. The neutrons form a neutron beam, and the neutron beam defines a main axis X3. The retarder 53 decelerates the neutrons generated from the target 52 to superheat In the neutron energy zone, the reflector 54 guides the neutrons deviated from the main axis X3 back to the main axis X3 to increase the intensity of the epithermal neutron beam. The retarder 53 is arranged as two cones adjacent to each other in opposite directions. The retarder 53 The left side of the retarder 53 is in the shape of a cylinder, and the right side of the retarder 53 is in the shape of a cone that gradually becomes smaller toward the right. The radiation shield 26 is used to shield the leaked neutrons and photons to reduce the normal tissue dose in the non-irradiated area.

As a preference, the target 52, retarder 53, reflector 54, thermal neutron absorber 55 and radiation shield 56 in the fifth embodiment can be the same as those in the first embodiment, and the radiation shield therein 56 includes a photon shield 561 made of lead (Pb) and a neutron shield 562 made of polyethylene (PE), which may be provided at the beam exit 57 . An air duct 58 is arranged between the thermal neutron absorber 55 and the beam outlet 57 . The prosthesis B3 is placed approximately 1 cm from the beam exit 57 .

Adopt MCNP software below to the simulation calculation of the retarder of double cone in the second embodiment, the retarder of the cylinder in the fourth embodiment and the cylinder+cone in the fifth embodiment:

Wherein, following table four has shown the performance of beam quality factor in the air in these three kinds of embodiments:

Table 4: Beam Quality Factors in Air

Wherein, the following table five shows the performance of dosage performance in these three kinds of embodiments:

Table 5: Dose Performance

dose performance Cylinder cylinder + cone double cone effective treatment depth 11.8 10.9 10.9 effective treatment depth dose rate 2.95 4.28 4.47 Effective therapeutic dose ratio 5.52 5.66 5.66

Wherein, the following table six shows the simulated values of the parameters for evaluating the performance of the neutron beam dose in these three embodiments:

Table 6: Parameters for evaluating neutron beam dose performance

parameters Cylinder cylinder + cone double cone Irradiation time (10mA) 40.7 26.1 25.3 30.0RBE-Gy treatable depth 8.4 7.6 7.7 tumor maximum dose 70.9 67.4 68.5 normal brain tissue maximum dose 12.0 11.2 11.3 skin maximum dose 11.0 11.0 11.0

Note: From the above three tables, it can be known that if the retarder is set in at least one cone shape, the treatment benefit of the sub-beam is better.

The "column" or "cylindrical shape" mentioned in the embodiments of the present utility model refers to a structure whose overall trend of the outer contour is basically unchanged from one side to the other side along the direction shown in the figure, and one of the outer contours The contour line can be a line segment, such as the corresponding contour line of a cylinder, or a circular arc close to the line segment with a large curvature, such as a corresponding contour line of a spherical body with a large curvature. The entire surface of the outer contour can be A smooth transition can also be a non-smooth transition, such as making a lot of protrusions and grooves on the surface of a cylinder or a spherical body with a large curvature.

The "cone" or "cone-shaped" mentioned in the embodiment of the utility model refers to a structure whose overall trend of the outer contour gradually becomes smaller along the direction shown in the figure from one side to the other side, one of the outer contours The contour line can be a line segment, such as a cone-shaped corresponding contour line, or a circular arc, such as a spherical body-shaped corresponding contour line. The entire surface of the outer contour can be a smooth transition or a non-smooth transition. For example, many protrusions and grooves are made on the surface of a cone or a sphere.

The beam shaping body for neutron capture therapy disclosed by the utility model is not limited to the contents described in the above embodiments and the structures shown in the accompanying drawings. Obvious changes, substitutions or modifications made to the materials, shapes and positions of the components on the basis of the present utility model are all within the protection scope of the utility model.

Claims (10)

1. A beam shaper for neutron capture therapy, characterized in that: the beam shaper includes a beam entrance, a target, a retarder adjacent to the target, surrounded by the retarder A reflector outside the velocity body, a thermal neutron absorber adjacent to the retarder, a radiation shield and a beam exit arranged in the beam shaping body, the target material and the proton incident from the beam entrance the beam undergoes a nuclear reaction to produce neutrons forming a neutron beam defining a major axis, the retarder decelerating neutrons produced from the target to epithermal neutrons In an energy zone, the retarder is configured to include at least one cone-like shape, and the reflector guides neutrons deviated from the main axis back to the main axis to increase the intensity of the epithermal neutron beam, and the thermal center The sub-absorber is used to absorb thermal neutrons to avoid excessive doses to shallow normal tissues during treatment, and the radiation shield is used to shield leaked neutrons and photons to reduce normal tissue doses in non-irradiated areas. 2. The beam shaper for neutron capture therapy according to claim 1, characterized in that: the beam shaper is further used in accelerator boron neutron capture therapy. 3. The beam shaping body for neutron capture therapy according to claim 2, characterized in that: the accelerator boron neutron capture therapy accelerates the proton beam through an accelerator, the target material is made of metal, and the proton beam The beam is accelerated to an energy sufficient to overcome the Coulomb repulsion of the target nuclei and undergo a nuclear reaction with the target to produce neutrons. 4. The beam shaping body for neutron capture therapy according to claim 1, characterized in that: said beam shaping body can retard neutrons to the epithermal neutron energy region, and reduce thermal neutrons and Fast neutron content, the epithermal neutron energy range is between 0.5eV and 40keV, the thermal neutron energy range is less than 0.5eV, the fast neutron energy range is greater than 40keV, and the retarder is composed of fast neutrons The reflector is made of a material with a large interaction section and a small epithermal neutron interaction section, the reflector is made of a material with strong neutron reflection ability, and the thermal neutron absorber is made of a material with a large interaction section with thermal neutrons become. 5. The beam shaper for neutron capture therapy according to claim 4, characterized in that: the retarder is made of D ₂ O, AlF ₃ , Fluental ^TM , CaF ₂ , Li ₂ CO ₃ , MgF ₂ and Al ₂ O ₃ at least one. 6. The beam shaper for neutron capture therapy according to claim 4, characterized in that: the reflector is made of at least one of Pb or Ni. 7. The beam shaper for neutron capture therapy according to claim 4, characterized in that: the thermal neutron absorber is made of ⁶ Li, the thermal neutron absorber and the beam Air channels are provided between the outlets. 8. The beam shaper for neutron capture therapy according to claim 1, wherein the radiation shielding comprises photon shielding and neutron shielding. 9. The beam shaper for neutron capture therapy according to claim 1, characterized in that: the retarder is configured to include a cylinder and a cone adjacent to the cylinder shape. 10 . The beam shaper for neutron capture therapy according to claim 1 , wherein the retarder is arranged in the shape of two cones adjacent to each other in opposite directions. 11 .