CN108042930B - Beam shaping body for neutron capture therapy - Google Patents
Beam shaping body for neutron capture therapy Download PDFInfo
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Abstract
In order to improve the flux and quality of a neutron source, one aspect of the invention provides a beam shaper for neutron capture therapy, wherein the beam shaper comprises a target material, a retarder adjacent to the target material, a reflector surrounding the retarder, a thermal neutron absorber adjacent to the retarder, a radiation shield arranged in the beam shaper and a beam outlet, the target material undergoes nuclear reaction with a proton beam incident from the beam inlet to produce neutrons, the neutrons form a neutron beam, the neutron beam defines an axis, the retarder decelerates neutrons produced from the target material to a epithermal neutron energy region, the reflector guides neutrons away from the axis back to the axis to increase the intensity of the epithermal neutron beam, a gap channel is arranged between the retarder and the reflector to increase the epithermal neutron flux, the thermal neutron absorber is used for absorbing thermal neutrons to avoid excessive dose with normal tissues in a shallow layer during therapy, radiation shielding is used to shield the leak neutrons and photons from reducing the normal tissue dose in the non-illuminated areas.
Description
Technical Field
The present invention relates to a beam shaper, in particular a beam shaper for neutron capture therapy.
Background
With the development of atomic science, radiation therapy such as cobalt sixty, linacs, electron beams, etc. has become one of the main means of cancer treatment. However, the traditional photon or electron therapy is limited by the physical conditions of the radiation, and can kill tumor cells and damage a large amount of normal tissues in the beam path; in addition, due to the difference in the sensitivity of tumor cells to radiation, conventional radiotherapy is often ineffective in treating malignant tumors with relatively high radiation resistance, such as multiple glioblastoma multiforme (glioblastoma multiforme) and melanoma (melanoma).
In order to reduce the radiation damage of normal tissues around tumor, the target therapy concept in chemotherapy (chemotherapy) is applied to radiotherapy; for tumor cells with high radiation resistance, radiation sources with high Relative Biological Effect (RBE) are also actively developed, such as proton therapy, heavy particle therapy, neutron capture therapy, etc. Wherein, the neutron capture treatment combines the two concepts, such as boron neutron capture treatment, and provides better cancer treatment selection than the traditional radioactive rays by the specific accumulation of boron-containing drugs in tumor cells and the precise neutron beam regulation.
Boron Neutron Capture Therapy (BNCT) utilizes Boron-containing (B: (B-N-C-B-N-C-10B) The medicine has the characteristic of high capture cross section for thermal neutrons10B(n,α)7Li neutron capture and nuclear fission reaction generation4He and7li two heavily charged particles. Referring to FIGS. 1 and 2, schematic and graphical illustrations of boron neutron capture reactions are shown, respectively10B(n,α)7The Li neutron capture nuclear reaction equation has the average energy of two charged particles of about 2.33MeV, high Linear Energy Transfer (LET) and short-range characteristics, and the Linear energy transfer and the range of α particles are 150 keV/mum and 8μm respectively7The Li heavily-charged particles are 175 keV/mum and 5μm, the total range of the two particles is about equal to the size of a cell, so the radiation damage to organisms can be limited at the cell level, when boron-containing drugs selectively gather in tumor cells, and a proper neutron source is matched, the aim of locally killing the tumor cells can be achieved on the premise of not causing too much damage to normal tissues.
The effect of boron neutron capture therapy is also called binary cancer therapy (binary cancer therapy) because the effect depends on the boron-containing drug concentration and the quantity of thermal neutrons at the tumor cell position; it is known that, in addition to the development of boron-containing drugs, the improvement of neutron source flux and quality plays an important role in the research of boron neutron capture therapy.
Disclosure of Invention
In order to improve the flux and quality of a neutron source, one aspect of the invention provides a beam shaper for neutron capture therapy, wherein the beam shaper comprises a target material, a retarder adjacent to the target material, a reflector surrounding the retarder, a thermal neutron absorber adjacent to the retarder, a radiation shield arranged in the beam shaper and a beam outlet, the target material undergoes nuclear reaction with a proton beam incident from the beam inlet to produce neutrons, the neutrons form a neutron beam, the neutron beam defines an axis, the retarder decelerates neutrons produced from the target material to a epithermal neutron energy region, the reflector guides neutrons away from the axis back to the axis to increase the intensity of the epithermal neutron beam, a gap channel is arranged between the retarder and the reflector to increase the epithermal neutron flux, the thermal neutron absorber is used for absorbing thermal neutrons to avoid excessive dose with normal tissues in a shallow layer during therapy, radiation shielding is used to shield the leak neutrons and photons from reducing the normal tissue dose in the non-illuminated areas.
The beam shaper is further used for accelerator boron neutron capture therapy.
Accelerator boron neutron capture therapy accelerates a proton beam by an accelerator, the target is made of metal, and the proton beam is accelerated to energy enough to overcome the coulomb repulsion of the target atomic nucleus and generates nuclear reaction with the target to generate neutrons.
The beam shaper can retard neutrons to a super-thermal neutron energy region, the content of thermal neutrons and fast neutrons is reduced, the super-thermal neutron energy region is between 0.5eV and 40keV, the thermal neutron energy region is smaller than 0.5eV, the fast neutron energy region is larger than 40keV, the retarder is made of a material with a large fast neutron action section and a small super-thermal neutron action section, the reflector is made of a material with strong neutron reflection capacity, and the thermal neutron absorber is made of a material with a large thermal neutron action section.
Preferably, the retarder consists of D2O、AlF3、FluentalTM、CaF2、Li2CO3、MgF2And Al2O3At least one of (a).
Further, the reflector is made of at least one of Pb or Ni, and the thermal neutron absorber is made of6And an air channel is arranged between the thermal neutron absorber and the beam outlet.
The radiation shield includes a photon shield and a neutron shield. As a preference, the photon shield is made of Pb and the neutron shield is made of PE (polyethylene).
Preferably, the retarder is provided in a shape including one columnar shape and one conical shape adjacent to the columnar shape, or in two conical shapes adjacent to each other in opposite directions.
The "column" or "column-shaped" in the embodiment of the present invention refers to a structure in which the overall trend of the outer contour of one side of the outer contour to the other side of the outer contour along the direction shown in the figure is basically unchanged, one of the contour lines of the outer contour may be a line segment, such as a corresponding contour line of a cylindrical shape, or an arc close to the line segment with a larger curvature, such as a corresponding contour line of a spherical shape with a larger curvature, and the entire surface of the outer contour may be in smooth transition, or in non-smooth transition, such as a plurality of protrusions and grooves are formed on the surface of the cylindrical shape or the spherical shape with a larger curvature.
The "cone" or "cone-shaped" in the embodiments of the present invention refers to a structure in which the overall trend of the outer contour gradually decreases from one side to the other side along the direction shown in the figure, one of the contour lines of the outer contour may be a line segment, such as a corresponding contour line in a cone shape, or may be an arc, such as a corresponding contour line in a sphere shape, and the entire surface of the outer contour may be in a smooth transition, or may be in a non-smooth transition, such as a large number of protrusions and grooves are made on the surface in a cone shape or a sphere shape.
Drawings
FIG. 1 is a schematic diagram of a boron neutron capture reaction.
FIG. 2 is10B(n,α)7Li neutron capture nuclear reaction equation.
Fig. 3 is a schematic plan view of a beam shaper for neutron capture therapy in a first embodiment of the invention, wherein a clearance channel is provided between the retarder and the reflector.
Fig. 4 is a schematic plan view of a beam shaper for neutron capture therapy in a second embodiment of the invention, wherein the moderator is provided as a double cone and the interstitial channel locations in the first embodiment are filled with moderator material.
Fig. 5 is a schematic plan view of a beam shaper for neutron capture therapy in a third embodiment of the invention, wherein the retarders are arranged as double cones and the interstitial channel locations in the first embodiment are filled with reflector material.
FIG. 6 is a neutron yield plot of neutron energy versus neutron angle double differential.
Fig. 7 is a schematic plan view of a beam shaper for neutron capture therapy in a fourth embodiment of the invention, wherein the retarder is arranged as a cylinder.
Fig. 8 is a schematic plan view of a beam shaper for neutron capture therapy in a fifth embodiment of the invention, wherein the retarder is arranged as a cylinder + cone.
Detailed Description
Neutron capture therapy has been increasingly used in recent years as an effective means of treating cancer, with boron neutron capture therapy being the most common, the neutrons that supply boron neutron capture therapy being supplied by nuclear reactors or accelerators. The embodiments of the present invention are exemplified by an accelerator boron neutron capture therapy, the basic components of which generally include an accelerator for accelerating charged particles (e.g., protons, deuterons, etc.), a target and heat removal system, and a beam shaper, wherein the accelerated charged particles interact with a metal target to generate neutrons, and the appropriate nuclear reactions are selected according to the desired neutron yield and energy, the available energy and current of the accelerated charged particles, the physical properties of the metal target, and the like, and the nuclear reactions in question are generally characterized by7Li(p,n)7Be and9Be(p,n)9b, both reactions are endothermic. The energy thresholds of the two nuclear reactions are 1.881MeV and 2.055MeV respectively, because the ideal neutron source for boron neutron capture treatment is epithermal neutrons with keV energy level, theoretically if a metallic lithium target is bombarded by protons with energy only slightly higher than the threshold, neutrons with relatively low energy can Be generated, and the metallic lithium target can Be used clinically without too much slowing treatment, however, the proton interaction cross section of the two targets of lithium metal (Li) and beryllium metal (Be) and the threshold energy is not high, and in order to generate enough neutron flux, protons with higher energy are usually selected to initiate the nuclear reaction.
The ideal target material should have the characteristics of high neutron yield, neutron energy distribution generated close to the super-thermal neutron energy region (described in detail below), no generation of too much intense penetrating radiation, safety, cheapness, easy operation, high temperature resistance, etc., but actually, no nuclear reaction meeting all requirements can be found, and the target material made of lithium metal is adopted in the embodiment of the invention. It is well known to those skilled in the art that the material of the target may be made of other metallic materials than those mentioned above.
The requirements for the heat removal system vary depending on the nuclear reaction chosen, e.g.7Li(p,n)7Be has a higher requirement for a heat removal system due to the difference between the melting point and the thermal conductivity of the metal target (lithium metal)9Be(p,n)9B is high. In the embodiment of the invention7Li(p,n)7Nuclear reaction of Be.
Whether the neutron source of boron neutron capture treatment comes from nuclear reactor or the nuclear reaction of charged particles of an accelerator and a target material, a mixed radiation field is generated, namely a beam comprises neutrons and photons with low energy and high energy; for boron neutron capture therapy of deep tumors, the greater the amount of radiation other than epithermal neutrons, the greater the proportion of non-selective dose deposition in normal tissue, and therefore the unnecessary dose of radiation that these would cause should be minimized. In addition to the air beam quality factor, in order to better understand the dose distribution caused by neutrons in the human body, the embodiment of the present invention uses a human head tissue prosthesis to perform dose calculation, and uses the prosthesis beam quality factor as a design reference of the neutron beam, which will be described in detail below.
The International Atomic Energy Agency (IAEA) gives five air beam quality factor suggestions aiming at a neutron source for clinical boron neutron capture treatment, and the five suggestions can be used for comparing the advantages and disadvantages of different neutron sources and serving as reference bases for selecting neutron generation paths and designing beam integrators. The five proposals are as follows:
epithermal neutron beam flux Epithermal neutron flux>1 x 109n/cm2s
Fast neutron contamination<2 x 10-13Gy-cm2/n
Photon contamination of Photon contamination<2 x 10-13Gy-cm2/n
Thermal to epithermal neutron flux ratio of thermal to epithermal neutron flux ratio <0.05
Neutron current to flux ratio epithermal neutron current to flux ratio >0.7
Note: the super-thermal neutron energy region is between 0.5eV and 40keV, the thermal neutron energy region is less than 0.5eV, and the fast neutron energy region is greater than 40 keV.
1. Epithermal neutron beam flux:
the neutron beam flux and the boron-containing drug concentration in the tumor together determine the clinical treatment time. If the concentration of the boron-containing drug in the tumor is high enough, the requirement on the neutron beam flux can be reduced; conversely, if the boron-containing drug concentration in the tumor is low, high-throughput epithermal neutrons are required to administer a sufficient dose to the tumor. IAEA requirements for epithermal neutron beam flux are greater than 10 epithermal neutrons per second per square centimeter9The neutron beam at this flux can generally control the treatment time within one hour for the current boron-containing drugs, and the short treatment time can effectively utilize the limited residence time of the boron-containing drugs in the tumor besides having advantages on the positioning and comfort of the patient.
2. Fast neutron contamination:
since fast neutrons cause unnecessary normal tissue doses and are therefore considered contamination, the dose magnitude and neutron energy are positively correlated, and the fast neutron content should be minimized in the neutron beam design. Fast neutron contamination is defined as the fast neutron dose accompanied by a unit epithermal neutron flux, and the recommendation for fast neutron contamination by IAEA is less than 2 x 10-13Gy-cm2/n。
3. Photon contamination (gamma ray contamination):
gamma rays belong to intense penetrating radiation and can non-selectively cause the deposition of dose on all tissues on a beam path, so that the reduction of the content of the gamma rays is also a necessary requirement for neutron beam design, the gamma ray pollution is defined as the gamma ray dose accompanied by unit epithermal neutron flux, and the recommendation of IAEA for the gamma ray pollution is less than 2 x 10-13Gy-cm2/n。
4. Thermal neutron to epithermal neutron flux ratio:
because the thermal neutrons have high attenuation speed and poor penetrating power, most energy is deposited on skin tissues after entering a human body, and the thermal neutrons content is reduced aiming at deep tumors such as brain tumors and the like except that the epidermal tumors such as melanoma and the like need to use thermal neutrons as a neutron source for boron neutron capture treatment. The IAEA to thermal neutron to epithermal neutron flux ratio is recommended to be less than 0.05.
5. Neutron current to flux ratio:
the neutron current-to-flux ratio represents the beam directivity, the larger the ratio is, the better the neutron beam directivity is, the neutron beam with high directivity can reduce the dosage of the surrounding normal tissues caused by neutron divergence, and in addition, the treatable depth and the positioning posture elasticity are also improved. The IAEA to neutron current to flux ratio is recommended to be greater than 0.7.
The prosthesis is used to obtain the dose distribution in the tissue, and the quality factor of the prosthesis beam is deduced according to the dose-depth curve of the normal tissue and the tumor. The following three parameters can be used to make comparisons of therapeutic benefits of different neutron beams.
1. Effective treatment depth:
the tumor dose is equal to the depth of the maximum dose of normal tissue, after which the tumor cells receive a dose less than the maximum dose of normal tissue, i.e. the advantage of boron neutron capture is lost. This parameter represents the penetration of the neutron beam, with greater effective treatment depth indicating a greater depth of tumor that can be treated, in cm.
2. Effective treatment depth dose rate:
i.e. the tumor dose rate at the effective treatment depth, is also equal to the maximum dose rate for normal tissue. Because the total dose received by normal tissues is a factor influencing the size of the total dose which can be given to the tumor, the parameter influences the length of the treatment time, and the larger the effective treatment depth dose rate is, the shorter the irradiation time required for giving a certain dose to the tumor is, and the unit is cGy/mA-min.
3. Effective therapeutic dose ratio:
the average dose ratio received from the surface of the brain to the effective treatment depth, tumor and normal tissues, is called the effective treatment dose ratio; the average dose can be calculated by integrating the dose-depth curve. The larger the effective therapeutic dose ratio, the better the therapeutic benefit of the neutron beam.
In order to make the beam shaper design more dependent, in addition to the five IAEA proposed beam quality factors in air and the three parameters mentioned above, the following parameters for evaluating the performance of neutron beam dose are also utilized in the embodiments of the present invention:
1. the irradiation time is less than or equal to 30min (proton current used by an accelerator is 10mA)
2. 30.0RBE-Gy for treating depth greater than or equal to 7cm
3. Maximum tumor dose is more than or equal to 60.0RBE-Gy
4. Maximum dose of normal brain tissue is less than or equal to 12.5RBE-Gy
5. Maximum skin dose not greater than 11.0RBE-Gy
Note: RBE (relative Biological effect) is the relative Biological effect, and since the Biological effects caused by photons and neutrons are different, the above dose terms are multiplied by the relative Biological effects of different tissues to obtain the equivalent dose.
To improve the flux and quality of the neutron source, embodiments of the present invention are directed to improvements in beam shapers for neutron capture therapy, and preferably, accelerator boron neutron capture therapy. As shown in fig. 3, a beam shaper 10 for neutron capture therapy according to a first embodiment of the present invention includes a beam inlet 11, a target 12, a retarder 13 adjacent to the target 12, a reflector 14 surrounding the retarder 13, a thermal neutron absorber 15 adjacent to the retarder 13, a radiation shield 16 disposed within the beam shaper 10, and a beam outlet 17, wherein the target 12 is nuclear-reacted with a proton beam incident from the beam inlet 11 to generate neutrons, the neutrons forming a neutron beam, the neutron beam defining an axis X, the retarder 13 moderating the neutrons generated from the target 12 to a epithermal neutron energy region, the reflector 14 guiding neutrons away from the axis X back to the axis X to increase epithermal neutron beam intensity, a gap channel 18 is disposed between the retarder 13 and the reflector 14 to increase epithermal neutron flux, the thermal neutron absorber 15 is used to absorb thermal neutrons to avoid overdosing with shallow normal tissues during therapy, the radiation shield 16 serves to shield the leak neutrons and photons from normal tissue dose in the non-illuminated region.
Accelerator boron neutron capture therapy by addingThe accelerator accelerates the proton beam, which in a preferred embodiment is made of lithium metal, toward the target 12 at an energy sufficient to overcome coulomb repulsion of the target nuclei7Li(p,n)7Be nuclei react to produce neutrons. The beam shaping body 10 can slow down neutrons to a super-thermal neutron energy region and reduce the content of thermal neutrons and fast neutrons, the slowing body 13 is made of a material with a large fast neutron action section and a small super-thermal neutron action section, and as a preferred embodiment, the slowing body 13 is made of D2O、AlF3、FluentalTM、CaF2、Li2CO3、MgF2And Al2O3At least one of (a). The reflector 14 is made of a material having a strong neutron reflecting ability, and 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 having a large cross section for thermal neutron action, and as a preferred embodiment, the thermal neutron absorber 15 is made of6Li, an air channel 19 is provided between the thermal neutron absorber 15 and the beam outlet 17. 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).
The retarder 13 is formed in two conical shapes adjacent to each other in opposite directions, and as shown in fig. 3, the left side of the retarder 13 is formed in a conical shape gradually decreasing toward the left side, and the right side of the retarder 13 is formed in a conical shape gradually decreasing toward the right side, and both are adjacent to each other. Preferably, the left side of the retarder 13 is provided with a cone shape gradually decreasing toward the left side, and the right side may be provided with another shape adjacent to the cone shape, such as a column shape. The reflector 14 is tightly enclosed around the retarder 13, and a gap channel 18 is arranged between the retarder 13 and the reflector 14, wherein the gap channel 18 refers to an empty area which is not covered by a solid material and is easy for neutron beams to pass through, for example, the gap channel 18 can be set as an air channel or a vacuum channel. The thermal neutron absorber 15 disposed adjacent to the retarder 13 is composed of a very thin layer6Light made of Li material and made of Pb in the radiation shield 16The sub-shield 161 may be provided integrally or separately with the reflector 14, while the neutron shield 162 made of PE in the radiation shield 16 may be provided adjacent to the beam exit 17. An air channel 19 is provided between the thermal neutron absorber 15 and the beam outlet 17, where neutrons off axis X can be continuously directed back to axis X to increase epithermal neutron beam intensity. The prosthesis B is arranged at a distance of about 1cm from the beam outlet 17. It is well known to those skilled in the art that the photon shield 161 can be made of other materials so long as it functions to shield photons, and the neutron shield 162 can be made of other materials and can be disposed elsewhere so long as it meets the condition of shielding the neutrons from leakage.
In order to compare the differences between a beam shaper provided with interstitial channels and a beam shaper not provided with interstitial channels, a second embodiment in which the interstitial channels are filled with retarders and a third embodiment in which the interstitial channels are filled with reflectors is shown in fig. 4 and 5, respectively. Referring first to fig. 4, the beam shaper 20 includes a beam inlet 21, a target 22, a retarder 23 adjacent to the target 22, a reflector 24 surrounding the retarder 23, a thermal neutron absorber 25 adjacent to the retarder 23, a radiation shield 26 disposed within the beam shaper 20, and a beam outlet 27, the target 22 undergoing a nuclear reaction with a proton beam incident from the beam inlet 21 to generate neutrons, the neutrons forming a neutron beam, the neutron beam defining an axis X1, the retarder 23 decelerating the neutrons generated from the target 22 to a epithermal neutron energy region, the reflector 24 directing neutrons away from the axis X1 back to the axis X1 to increase the epithermal neutron beam intensity, the retarder 23 being disposed in two cone shapes adjacent to each other in opposite directions, the left side of the retarder 23 being a cone shape that gradually tapers toward the left side, the right side of the retarder 23 being a cone shape that gradually tapers toward the right side, adjacent to each other, a thermal neutron absorber 25 for absorbing thermal neutrons to avoid excessive dose with shallow normal tissue during treatment, and a radiation shield 26 for shielding leaked neutrons and photons to reduce normal tissue dose in non-irradiated areas.
As a preference, the target 22, the retarder 23, the reflector 24, the thermal neutron absorber 25, and the radiation shield 26 in the second embodiment may be the same as those in the first embodiment, and the radiation shield 26 therein includes a photon shield 261 made of lead (Pb) and a neutron shield 262 made of Polyethylene (PE), and the neutron shield 262 may be disposed at the beam exit 27. An air channel 28 is provided between the thermal neutron absorber 25 and the beam outlet 27. The prosthesis B1 was placed at a distance of about 1cm from the beam outlet 27.
Referring to fig. 5, the beam shaper 30 includes a beam inlet 31, a target 32, a retarder 33 adjacent to the target 32, a reflector 34 surrounding the retarder 33, a thermal neutron absorber 35 adjacent to the retarder 33, a radiation shield 36 disposed within the beam shaper 30, and a beam outlet 37, wherein the target 32 is nuclear-reacted with a proton beam incident from the beam inlet 31 to generate neutrons, which form a neutron beam, the neutron beam defining an axis X2, the retarder 33 decelerates the neutrons generated from the target 32 to a epithermal neutron energy region, the reflector 34 guides the neutrons away from the axis X2 to an axis X2 to increase the epithermal neutron beam intensity, the retarder 33 is disposed in two cone shapes adjacent to each other in opposite directions, a left side of the retarder 33 is a cone shape gradually decreasing toward the left side, a right side of the retarder 33 is a cone shape gradually decreasing toward the right side, and the two cone shapes are adjacent to each other, the thermal neutron absorber 35 is used to absorb thermal neutrons to avoid excessive doses with shallow normal tissue during treatment, and the radiation shield 36 is used to shield the leaking neutrons and photons to reduce the normal tissue dose in non-irradiated areas.
As a preference, the target 32, the retarder 33, the reflector 34, the thermal neutron absorber 35, and the radiation shield 36 in the third embodiment may be the same as those in the first embodiment, and the radiation shield 36 therein includes a photon shield 361 made of lead (Pb) and a neutron shield 362 made of Polyethylene (PE), and the neutron shield 362 may be provided at the beam exit 37. An air channel 38 is provided between the thermal neutron absorber 35 and the beam outlet 37. Prosthesis B2 was placed at about 1cm from beam exit 37.
The following simulated calculations for these three examples are performed using MCNP software (a general software package developed by los alamos national laboratory (los alamos national laboratory) in the united states based on monte carlo method for calculating neutron, photon, charged particle or coupled neutron/photon/charged particle transport problems in three-dimensional complex geometries):
the following table one shows the performance of the beam quality factor in air in the three embodiments (the units of the names in the table are as described above, and are not repeated here, and the same below):
table one: quality factor of air jet
Wherein the following table two shows the performance of the dosage table in these three embodiments:
table two: dose presentation
| Dose presentation | Retarder filling gap channel | Reflector filled gap channel | Gap channel |
| Effective depth of treatment | 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 simulation values of the parameters for evaluating the performance of neutron beam dosage in the three embodiments:
table three: parameters for evaluating whether neutron beam dose performance is good or bad
Note: from the three tables mentioned above, it can be seen that: a beam shaper with a gap channel between the retarder and the reflector, wherein the therapeutic benefit of the sub-beams is the best.
Since neutrons generated from the lithium target have a characteristic of higher forward average energy, as shown in fig. 6, the average neutron energy of the neutron scattering angle between 0 ° and 30 ° is about 478keV, while the average neutron energy of the neutron scattering angle between 30 ° and 180 ° is only about 290keV, if the geometry of the beam shaper is changed to cause more collisions between the forward neutrons and the retardance body, and less collisions between the lateral neutrons and the beam exit are required, the neutron retardance can be theoretically optimized, and the epithermal neutron flux can be efficiently increased. The effect of the geometry of the different beam shapers on the epithermal neutron flux is evaluated below starting from the geometry of the beam shapers.
As shown in fig. 7, which shows the geometry of the beam shaper in the fourth embodiment, the beam shaper 40 comprises a beam inlet 41, a target 42, a retarder 43 adjacent to the target 42, a reflector 44 surrounding the retarder 43, a thermal neutron absorber 45 adjacent to the retarder 43, a radiation shield 46 arranged inside the beam shaper 40, the target 42 undergoing a nuclear reaction with a proton beam incident from the beam inlet 41 to generate neutrons, the retarder 43 moderating neutrons generated from the target 42 to a epithermal neutron energy region, the reflector 44 guiding back deviated neutrons to increase the epithermal neutron beam intensity, the retarder 43 being arranged in a cylindrical shape, preferably, a cylindrical shape, the thermal neutron absorber 45 absorbing thermal neutrons to avoid excessive dose with shallow normal tissues during treatment, the radiation shield 46 shielding leaked neutrons and photons to reduce the normal tissue dose in the non-irradiated region, an air passage 48 is provided between the thermal neutron absorber 45 and the beam outlet 47.
As shown in fig. 8, which illustrates the geometry of the beam shaper in the fifth embodiment, the beam shaper 50 includes a beam inlet 51, a target 52, a moderator 53 adjacent to the target 52, a reflector 54 surrounding the moderator 53, a thermal neutron absorber 55 adjacent to the moderator 53, a radiation shield 56 disposed within the beam shaper 50, and a beam outlet 57, the target 52 nuclear-reacts with a proton beam incident from the beam inlet 51 to produce neutrons, which form a neutron beam, the neutron beam defining an axis X3, the moderator 53 moderating the neutrons produced from the target 52 to a epithermal neutron energy region, the reflector 54 directing neutrons away from the axis X3 back to the axis X3 to increase the epithermal neutron beam intensity, the moderator 53 being disposed in two cone shapes abutting each other in opposite directions, the left side of the moderator 53 being a cylinder shape, the right side of the moderator 53 being a cone shape that gradually tapers to the right side, adjacent to each other, a thermal neutron absorber 25 for absorbing thermal neutrons to avoid excessive dose with shallow normal tissue during treatment, and a radiation shield 26 for shielding leaked neutrons and photons to reduce normal tissue dose in non-irradiated areas.
As a preference, the target 52, the retarder 53, the reflector 54, the thermal neutron absorber 55, and the radiation shield 56 in the fifth embodiment may be the same as those in the first embodiment, and the radiation shield 56 therein includes a photon shield 561 made of lead (Pb) and a neutron shield 562 made of Polyethylene (PE), and the neutron shield 562 may be provided at the beam outlet 57. An air passage 58 is provided between the thermal neutron absorber 55 and the beam outlet 57. The prosthesis B3 was placed at a distance of about 1cm from the beam outlet 57.
The following simulated calculations of the retardation body of the bicone of the second embodiment, the retardation body of the cylinder of the fourth embodiment and the cylinder + cone of the fifth embodiment using MCNP software:
wherein the behavior of the airborne beam quality factor in these three embodiments is shown in table four below:
table four: quality factor of air jet
Wherein the following table five shows the performance of the dosage table in these three embodiments:
table five: dose presentation
| Dose presentation | Column body | Column body + cone body | Double cone |
| Effective depth of treatment | 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 simulation values of the parameters for evaluating the performance of neutron beam dosage in the three embodiments:
table six: parameters for evaluating whether neutron beam dose performance is good or bad
| Parameter(s) | Column body | Column body + cone body | Double cone |
| Irradiation time (10mA) | 40.7 | 26.1 | 25.3 |
| 30.2RBE-Gy treatable depth | 8.4 | 7.6 | 7.7 |
| Maximum tumor dose | 70.9 | 67.4 | 68.5 |
| Maximum dose of normal brain tissue | 12.0 | 11.2 | 11.3 |
| Maximum dose to the skin | 11.0 | 11.0 | 11.0 |
Note: from the three tables mentioned above, it can be seen that: the retarding body is arranged into at least one cone shape, wherein the therapeutic benefit of the sub-beams is better.
The "column" or "column-shaped" in the embodiment of the present invention refers to a structure in which the overall trend of the outer contour of one side of the outer contour to the other side of the outer contour along the direction shown in the figure is basically unchanged, one of the contour lines of the outer contour may be a line segment, such as a corresponding contour line of a cylindrical shape, or an arc close to the line segment with a larger curvature, such as a corresponding contour line of a spherical shape with a larger curvature, and the entire surface of the outer contour may be in smooth transition, or in non-smooth transition, such as a plurality of protrusions and grooves are formed on the surface of the cylindrical shape or the spherical shape with a larger curvature.
The "cone" or "cone-shaped" in the embodiments of the present invention refers to a structure in which the overall trend of the outer contour gradually decreases from one side to the other side along the direction shown in the figure, one of the contour lines of the outer contour may be a line segment, such as a corresponding contour line in a cone shape, or may be an arc, such as a corresponding contour line in a sphere shape, and the entire surface of the outer contour may be in a smooth transition, or may be in a non-smooth transition, such as a large number of protrusions and grooves are made on the surface in a cone shape or a sphere shape.
The beam shaper for neutron capture therapy disclosed herein is not limited to the configurations described in the above embodiments and shown in the drawings. Obvious changes, substitutions or alterations of the materials, shapes and positions of the components in the invention are all within the scope of the invention as claimed.
Claims (10)
1. A beam shaper for neutron capture therapy, characterized by: the beam shaper includes a beam inlet, a target, a moderator adjacent to the target, a reflector surrounding outside the moderator, a radiation shield disposed within the beam shaper, and a beam outlet, the target undergoing a nuclear reaction with a proton beam incident from the beam inlet to produce neutrons that form a neutron beam, the moderator decelerating neutrons produced from the target to a super-thermal neutron energy region, the moderator having a first side proximate to the beam inlet and a second side distal from the beam inlet, the target being spaced from the beam outlet less than the first side to the beam outlet, the moderator disposed to include a first cone distal from the beam outlet, a portion of the beam inlet received within the first cone, another portion of the beam inlet received within the reflector, the reflector directing back deflected neutrons to increase the intensity of the super-thermal neutron beam, the radiation shield is used to shield the leak neutrons and photons from reducing the normal tissue dose in the non-illuminated region.
2. The beam shaper for neutron capture therapy of claim 1, wherein: the neutron beam defines an axis, the first side is a side of the first cone shape close to the beam inlet, the first cone shape further comprises a third side far away from the beam inlet, the outer contour of the first cone shape gradually decreases along the overall trend from the third side to the first side, and the target is located between the first side and the third side in the axis direction.
3. The beam shaper for neutron capture therapy of claim 2, wherein: the retarder is further provided with a second cone which is adjacent to the first cone and is close to the beam outlet, the second side is one side of the second cone, which is close to the beam outlet, the second cone further comprises a fourth side far away from the beam outlet, and the outer contour of the second cone gradually becomes smaller along the whole trend from the fourth side to the second side.
4. The beam shaper for neutron capture therapy of claim 2, wherein: the retarding body is also provided with a cylinder which is adjacent to the first cone and is close to the beam outlet, and the second side is one side of the cylinder which is close to the beam outlet.
5. The beam shaper for neutron capture therapy of claim 1, wherein: the neutron beam defines an axis, the retarder is provided with at least one cylinder far away from the beam outlet, the first side is one side of the cylinder close to the beam inlet, the cylinder further comprises a third side far away from the beam inlet, and the target is located between the first side and the third side in the axis direction.
6. The beam shaper for neutron capture therapy of claim 1, wherein: the beam shaper is further used for accelerator boron neutron capture therapy, wherein the accelerator boron neutron capture therapy accelerates a proton beam through an accelerator, the target is made of metal, and the proton beam is accelerated to energy enough to overcome the coulomb repulsion of the target atomic nucleus and generates a nuclear reaction with the target to generate neutrons.
7. The beam shaper for neutron capture therapy of claim 1, wherein: and a gap channel which is not covered by a solid body is arranged between the retarder and the reflector so as to improve the epithermal neutron flux.
8. The beam shaper for neutron capture therapy of claim 7, wherein: the beam shaper is further provided with a thermal neutron absorber adjacent to the retarder, the interstitial channel being surrounded by the reflector, the retarder and the thermal neutron absorber.
9. The beam shaper for neutron capture therapy of claim 1, wherein: the beam inlet, the retarder body and the beam outlet all extend along a neutron beam axis.
10. The beam shaper for neutron capture therapy of claim 1, wherein: the neutron beam defines an axis, the first side projects the target along the axis in a direction toward the beam inlet, and the second side projects the target along the axis in a direction toward the beam outlet.
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| CN201810009982.9A CN108042930B (en) | 2014-12-08 | 2014-12-08 | Beam shaping body for neutron capture therapy |
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| CN201810009982.9A CN108042930B (en) | 2014-12-08 | 2014-12-08 | Beam shaping body for neutron capture therapy |
| CN201410743692.9A CN104511096B (en) | 2014-12-08 | 2014-12-08 | Beam-shaping body for neutron capture treatment |
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| CN201410743692.9A Active CN104511096B (en) | 2014-12-08 | 2014-12-08 | Beam-shaping body for neutron capture treatment |
| CN201810009962.1A Active CN108325092B (en) | 2014-12-08 | 2014-12-08 | Beam shaping body for neutron capture therapy |
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| CN110251847A (en) * | 2015-05-04 | 2019-09-20 | 南京中硼联康医疗科技有限公司 | Beam-shaping body for neutron capture treatment |
| CN106310540A (en) * | 2015-05-04 | 2017-01-11 | 南京中硼联康医疗科技有限公司 | Beam shaping body for neutron capture therapy |
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| CN108042930A (en) | 2018-05-18 |
| CN104511096A (en) | 2015-04-15 |
| CN108325092A (en) | 2018-07-27 |
| CN108325092B (en) | 2020-08-07 |
| CN104511096B (en) | 2018-01-05 |
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Application publication date: 20180518 Assignee: China Boron (Xiamen) Medical Devices Co., Ltd. Assignor: NEUBORON MEDTECH LTD. Contract record no.: X2019320000054 Denomination of invention: Beam shaping body for neutron capture therapy License type: Common License Record date: 20190910 |
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