Radiation irradiation system and control method thereof

Abstract

The radiation irradiation system and control method thereof according to an embodiment of the present invention screens out elements that have an influence on the simulation calculation results of neutrons and photons in the application scenario of the radiation irradiation system by taking into account the weight proportion of elements in the human body and the reaction strength with neutrons and photons, and only simulates the screened elements during the simulation process, thereby greatly improving the calculation speed and reducing the calculation time.

Description

[Technical field]

[0001] One aspect of the present invention relates to a radiation irradiation system, and another aspect of the present invention relates to a method for controlling a radiation irradiation system. [Background technology]

[0002] 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, conventional photon or electron therapy kills tumor cells due to the limitations of the physical conditions of radiation itself, and also damages many normal tissues along the beam path. In addition, because tumor cells have different degrees of sensitivity to radiation, conventional radiation therapy is not very effective in treating malignant tumors with high radiation resistance (e.g., glioblastoma multiforme, melanoma).

[0003] To reduce radiation damage to normal tissues surrounding tumors, the concept of targeted therapy in chemotherapy has been applied to radiotherapy. In addition, for tumor cells with high radiation resistance, radiation sources with high relative biological effectiveness (RBE), such as proton therapy, heavy particle therapy, and neutron capture therapy, are currently being actively developed. Among these, neutron capture therapy is a combination of the above two concepts. For example, in boron neutron capture therapy (BNCT), boron-containing drugs are specifically concentrated in tumor cells, and combined with high-precision beam control, it provides a better cancer treatment option than conventional radiation.

[0004] Boron neutron capture therapy is a method to 10 B) Taking advantage of the property that the contained drug has a large capture cross section for thermal neutrons, 10 B(n,α) 7 Li Neutron capture and fission reactions 4 He and7 It generates two heavy charged particles, Li and Li. The total range of the two particles is approximately the size of a cell, so that the radiation damage to the living body is limited to the cellular level. The boron-containing drug can be selectively collected in tumor cells, and combined with an appropriate neutron beam source, it can achieve the goal of partially killing tumor cells without causing significant damage to normal tissues.

[0005] In order to allow the radioactive particles to kill as many cancer cells as possible while reducing damage to normal cells, a CT or PET imaging diagnosis is usually performed before treating the patient, and tissue material information of the human body is obtained based on the imaging diagnosis results, a calculation model is established based on the material information and the radiation source, the transport process of the radioactive particles in the human body is simulated, and finally the dose distribution of the radioactive particles in the human body is obtained, and the optimal plan of dose distribution for the patient is selected as the patient's treatment scheme.

[0006] At present, the dose calculation module in the radiation therapy planning system is mainly obtained by simulating the radiation particles by the Monte Carlo method. Conventional radiation therapy requires the simulation of the motion process of photons and electrons, while radiation irradiation therapy requires the simulation of the motion process of neutrons and photons. At present, the Monte Carlo method is the most accurate method for dose calculation, but the calculation is time-consuming and consumes a large amount of memory.

[0007] Currently, general-purpose Monte Carlo programs such as MCNP and Geant4 are often used for radiation therapy calculations. MCNP is first used for reactor design calculations, and Geant4 is first used for high-energy physics calculations. Since the physics scene of radiation therapy is not considered in the early stages of design, no special optimization is performed for radiation therapy calculations. The creation of a radiation therapy plan usually needs to be completed within a certain time. For example, radiation irradiation therapy requires that the radiation therapy planning system can create a treatment scheme within one hour. The dose calculation process takes up most of the time required to create a radiation therapy plan, so it is necessary to optimize the dose calculation method to reduce the time required to create a radiation therapy plan. Summary of the Invention

[0008] In order to overcome the deficiencies of the prior art, a radiation irradiation system according to a first aspect of the present invention includes a beam irradiation device that generates a therapeutic beam and irradiates an irradiated body with the therapeutic beam to form an irradiated area, a treatment planning module that performs dose simulation calculations based on parameters of the therapeutic beam and medical image data of the irradiated area and creates a treatment plan, and combines the weight percentage of elements in the human body and the reaction strength with neutrons and photons to screen elements that have an influence on the simulation calculation results of neutrons and photons in the application scene of the radiation irradiation system, and simulates only the screened elements during the simulation process, and a control module that controls the irradiation of the beam irradiation device based on the treatment plan.

[0009] In other embodiments, the elements screened by the treatment planning module are one or more elements selected from H, He, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca.

[0010] More specifically, the elements screened by the treatment planning module are H, He, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca.

[0011] In another embodiment, the treatment planning module removes from each element's corresponding neutron cross section database those databases corresponding to temperatures other than 294K and 0K.

[0012] The radiation irradiation system is preferably a neutron capture therapy system, and the beam irradiation device includes a neutron generator, a beam shaper and a treatment table, the neutron generator includes an accelerator and a target, the accelerator accelerates charged particles to generate a charged particle beam and interacts with the target to generate a neutron beam, the beam shaper is capable of adjusting the neutron beam generated by the neutron generator to a predetermined beam quality, and the neutron beam generated by the neutron generator passes through the beam shaper and is irradiated to an irradiated object on the treatment table.

[0013] A method for controlling a radiation irradiation system according to a second aspect of the present invention, comprising the steps of: Radiation irradiation system The radiation irradiation system includes a beam irradiation device that generates a therapeutic beam and irradiates the therapeutic beam onto an irradiated body to form an irradiated area, a treatment planning module that performs dose simulation calculations based on parameters of the treatment beam and medical image data of the irradiated area and creates a treatment plan, and a control module that controls irradiation by the beam irradiation device based on the treatment plan.The control method of the radiation irradiation system includes a step of screening elements that have an influence on the simulation calculation results of neutrons and photons in the application scene of the radiation irradiation system based on the weight proportion of elements in the human body and the reaction strength with neutrons and photons, and simulating only the screened elements in the simulation process.

[0014] In other embodiments, the elements screened by the treatment planning module are one or more elements selected from H, He, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca.

[0015] More specifically, the elements screened by the treatment planning module are H, He, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, Ar, K, and Ca.

[0016] In another embodiment, the control method further includes the step of the treatment planning module removing databases corresponding to temperatures other than 294K and 0K from the corresponding neutron cross section database for each element.

[0017] The radiation irradiation system is preferably a neutron capture therapy system, and the beam irradiation device includes a neutron generator, a beam shaper and a treatment table, the neutron generator includes an accelerator and a target, the accelerator accelerates charged particles to generate a charged particle beam and interacts with the target to generate a neutron beam, the beam shaper is capable of adjusting the neutron beam generated by the neutron generator to a predetermined beam quality, and the neutron beam generated by the neutron generator passes through the beam shaper and is irradiated to an irradiated object on the treatment table.

[0018] The radiation irradiation system and control method thereof according to an embodiment of the present invention screens out elements that have an influence on the simulation calculation results of neutrons and photons in the application scenario of the radiation irradiation system by taking into account the weight proportion of elements in the human body and the reaction strength with neutrons and photons, and only simulates the screened elements during the simulation process, thereby greatly improving the calculation speed of the treatment planning module and reducing the calculation time.

[0019] A radiation irradiation system according to a third aspect of the present invention includes: a beam irradiation device that generates a therapeutic beam and irradiates an irradiated body with the therapeutic beam to form an irradiated area; a treatment planning module that performs a dose simulation calculation based on parameters of the therapeutic beam and medical image data of the irradiated area and creates a treatment plan, the treatment planning module assigning simulation tasks of different radiation source particles to different processes or threads and collecting the calculation tasks of each process or thread after completion to obtain a final calculation result; and a control module that controls irradiation of the beam irradiation device based on the treatment plan.

[0020] The radiation irradiation system is preferably a neutron capture therapy system, the beam irradiation device including a neutron generator, a beam shaper and a treatment table, the neutron generator including an accelerator and a target, the accelerator accelerating charged particles to generate a charged particle beam and interacting with the target to generate a neutron beam, the beam shaper capable of adjusting the neutron beam generated by the neutron generator to a predetermined beam quality, and the neutron beam generated by the neutron generator passing through the beam shaper to be irradiated to the irradiated subject on the treatment table.

[0021] In one embodiment, particles are simulated by CPU process parallelism, thread parallelism and GPU acceleration, and both process parallelism and thread parallelism are realized by using a multi-core CPU to realize parallel calculation. The calculation process of CPU process parallelism and thread parallelism includes the following steps: first, the system obtains the number of processes or the number of threads to obtain a value n; then, the system uniformly divides the particles to be simulated into n; then, each thread or each process independently simulates and counts one particle; and finally, the system calculates the counts obtained in each process or each thread to obtain a final dose.

[0022] In one embodiment, GPU acceleration is realized by parallel calculation of the multi-core processor of the GPU, and the process of simulation calculation by GPU acceleration includes the steps of first, the system transferring random numbers, cross-sectional area data, etc. from the CPU memory to the GPU graphic memory, then, each processor in the GPU simulates, calculates, and counts a single particle, and statistically converts the counting result into a global count; and then, the system determines whether there are any unsimulated particles, and if there are no unsimulated particles, transfers the counting result from the GPU memory to the CPU memory; if there are unsimulated particles, it returns to the previous step and continues to simulate and count the unsimulated particles until the simulation of all particles is completed.

[0023] A method for controlling a radiation irradiation system according to a fourth aspect of the present invention, comprising the steps of: The radiation irradiation system the radiation irradiation system includes a beam irradiation device that generates a treatment beam and irradiates an irradiated body with the treatment beam to form an irradiated area; a treatment planning module that performs dose simulation calculations based on parameters of the treatment beam and medical image data of the irradiated area and creates a treatment plan; and a control module that controls irradiation by the beam irradiation device based on the treatment plan, and the control method of the radiation irradiation system includes a step of assigning simulation tasks of different source particles to different processes or threads, and consolidating the calculation tasks of each process or thread after completion to obtain a final calculation result.

[0024] In one embodiment, particles are simulated using CPU process parallelism, thread parallelism and GPU acceleration.

[0025] Preferably, both process parallelism and thread parallelism realize parallel calculations using a multi-core CPU.

[0026] In one embodiment, the process parallelism and thread parallelism calculation process of the CPU includes the steps of first, the system obtaining the number of processes or the number of threads to obtain a value n; then, the system uniformly dividing the particles to be simulated into n; then, independently simulating and counting one particle in each thread or process; and finally, the system collating the counts obtained in each process or thread to obtain a final dose.

[0027] Preferably, the GPU acceleration is achieved through parallel computation of a multi-core processor of the GPU.

[0028] The process of GPU-accelerated simulation calculation includes the steps of firstly, the system transferring random numbers, cross-sectional area data, etc. from CPU memory to GPU graphic memory, then, each processor in the GPU simulates, calculates, and counts a single particle, and stats the counting result into a global count, and then, the system determines whether there are any unsimulated particles, and if there are no unsimulated particles, transfers the counting result from the GPU memory to the CPU memory, and if there are unsimulated particles, returns to the previous step and continues to simulate and count the unsimulated particles until the simulation of all particles is completed.

[0029] The radiation irradiation system and its control method according to an embodiment of the present invention can significantly improve the calculation speed and reduce the calculation time by allocating simulation tasks of different source particles to different processes or threads, and consolidating the calculation tasks of each process or thread after they are completed to obtain the final calculation result.

[0030] A radiation irradiation system according to a fifth aspect of the present invention includes a beam irradiation device that generates a therapeutic beam and irradiates an irradiated body with the therapeutic beam to form an irradiated area, and a treatment planning module that performs a dose simulation calculation based on parameters of the therapeutic beam and medical image data of the irradiated area and creates a treatment plan, the treatment planning module stopping the simulation for photons when a half absorption thickness of photons is equal to or less than a first predetermined value, and a control module that controls irradiation of the beam irradiation device based on the treatment plan.

[0031] The radiation irradiation system is preferably a neutron capture therapy system, the beam irradiation device including a neutron generator, a beam shaper and a treatment table, the neutron generator including an accelerator and a target, the accelerator accelerating charged particles to generate a charged particle beam and interacting with the target to generate a neutron beam, the beam shaper capable of adjusting the neutron beam generated by the neutron generator to a predetermined beam quality, and the neutron beam generated by the neutron generator passing through the beam shaper to be irradiated to the irradiated subject on the treatment table.

[0032] In one embodiment, the treatment planning module calculates the half-absorption thickness t of the photon beam using equation (1-1):

number

[0033] The first predetermined value is the size of a single cell, preferably the first predetermined value is 0.2 mm, and when the photon energy is equal to or less than the second predetermined value, the photon half absorption thickness corresponding to the photon energy is equal to or less than the first predetermined value, and the second predetermined value is 10 KeV.

[0034] A method for controlling a radiation irradiation system according to a sixth aspect of the present invention, comprising the steps of: The radiation irradiation system the radiation irradiation system includes a beam irradiation device that generates a treatment beam and irradiates an irradiated body with the treatment beam to form an irradiated area; a treatment planning module that performs dose simulation calculations based on parameters of the treatment beam and medical image data of the irradiated area and creates a treatment plan; and a control module that controls irradiation by the beam irradiation device based on the treatment plan, wherein the control method for the radiation irradiation system includes a step of stopping simulation for photons when a half absorption thickness of the photons is equal to or less than a first predetermined value.

[0035] In one embodiment, the treatment planning module calculates the half-absorption thickness t of the photon beam using equation (1-1):

number

[0036] The first predetermined value is the size of a single cell.

[0037] Preferably, the first predetermined value is 0.2 mm.

[0038] When the photon energy is less than or equal to the second predetermined value, the photon half absorption thickness corresponding to the photon energy is less than or equal to the first predetermined value.

[0039] Preferably, the second predetermined value is 10 KeV.

[0040] The radiation irradiation system and control method thereof according to an embodiment of the present invention can reduce the calculation time while ensuring the calculation accuracy by stopping the simulation of the photons when the half-absorption depth of the photons is less than a first predetermined value.

[0041] A radiation irradiation system according to a seventh aspect of the present invention includes a beam irradiation device that generates a therapeutic beam and irradiates an irradiated body with the therapeutic beam to form an irradiated area, and a treatment planning module that performs dose simulation calculations based on parameters of the therapeutic beam and medical image data of the irradiated area and creates a treatment plan, the treatment planning module simulating particles by variance reduction, and a control module that controls irradiation of the beam irradiation device based on the treatment plan.

[0042] Further, variance reduction includes implicit absorption, weight window game, Russian roulette and splitting, and the radiation irradiation system is a neutron capture therapy system, the beam irradiation device includes a neutron generator, a beam shaper and a treatment table, the neutron generator includes an accelerator and a target, the accelerator accelerates charged particles to generate a charged particle beam and interacts with the target to generate a neutron beam, the beam shaper is capable of adjusting the neutron beam generated by the neutron generator to a predetermined beam quality, and the neutron beam generated by the neutron generator passes through the beam shaper and is irradiated to the subject on the treatment table.

[0043] A method for controlling a radiation irradiation system according to an eighth aspect of the present invention, comprising the steps of: Radiation irradiation system The radiation irradiation system includes a beam irradiation device that generates a treatment beam and irradiates an irradiated body with the treatment beam to form an irradiated area, a treatment planning module that performs dose simulation calculations based on parameters of the treatment beam and medical image data of the irradiated area and creates a treatment plan, and a control module that controls irradiation by the beam irradiation device based on the treatment plan, and the control method for the radiation irradiation system includes a step in which the treatment planning module simulates particles by variance reduction.

[0044] Further, the variance reduction includes implicit absorption, a weight window game, Russian roulette and splitting, and the steps of simulating a particle by variance reduction include step S1 of acquiring one source particle, step S2 of determining whether the particle collides in a lattice cell, and if it is determined that the particle collides, steps S3 and S4 are executed in order, and if it is determined that the particle does not collide, steps S5 and S6 are executed in order, step S3 of performing implicit absorption processing, step S4 of determining whether the weight is lower than the weight window, and if it is determined that the weight is lower, step S7 is executed, and if it is determined that the weight is not lower, step S5 returns to step S2, and step S6 of performing Russian roulette and splitting. The method includes step S5 of performing a pritting process, step S6 of determining whether or not to perform Russian roulette processing, and if it is determined that Russian roulette processing is to be performed, executing step S7, and returning to step S2 if it is determined that Russian roulette processing is not to be performed, step S7 of determining whether or not to annihilate, and if it is determined that to annihilate, executing step S8, and if it is determined that to not annihilate, executing step S9 and then returning to step S2, step S7 of determining whether or not particle processing is complete, and if it is determined that it is complete, ending the flow, and if it is determined that it is not complete, returning to step S1, and step S9 of dividing the weight by the annihilation probability.

[0045] Furthermore, Russian roulette and splitting include a step S1 of calculating and recording the lattice space importance of each lattice, a step S2 of acquiring particles, a step S3 of performing weight window detection and operation on the particles, and a step S4 of calculating the lattice space importance I before and after the particle crosses the lattice boundary. n and I n+1 Step S4 of calculating I n I n+1The method includes step S5 of comparing whether the particle is greater than the weighted particle, and if it is not greater, executing step S6 and then returning to step S3, and if it is greater, executing step S7; step S6 of splitting the particle and decreasing the weight of the particle; step S7 of determining whether to annihilate the particle, and if it is determined that the particle should be annihilated, executing step S9, and if it is determined that the particle should not be annihilated, executing step S8 and then returning to step S3; step S8 of increasing the weight of the particle; and step S9 of determining whether the simulation of the particle is completed, and if it is determined that the simulation is not completed, returning to step S2, and if it is determined that the simulation is completed, terminating.

[0046] Furthermore, the implicit absorption includes step S1 of acquiring particles, step S2 of determining whether the particles collide within a lattice cell, and if it is determined that the particles collide, executing step S3, and if it is determined that the particles do not collide, returning to step S1, step S3 of multiplying the weight by the scattering occurrence probability, step S4 of determining whether the weight of the particle is smaller than the lowest weight, and if it is determined that the weight is smaller, executing step S5, and if it is determined that the weight is not smaller, returning to step S2, step S5 of determining whether the particle is to be annihilated, and if it is determined that the particle is to be annihilated, executing step S7, and if it is determined that the particle is not to be annihilated, returning to step S2 after executing step S6, step S6 of dividing the weight by the annihilation probability, and step S7 of determining whether the simulation of the particle is completed, and if it is determined that the simulation is not completed, returning to step S1, and if it is determined that the simulation is completed, terminating.

[0047] Further, the weight window game includes step S1 of simulating particle movement, step S2 of determining whether the weight of the particle is within the weight window range, returning to step S1 if it is determined that it is within the range, and executing step S3 if it is determined that it is not within the range, step S3 of determining whether the weight is larger than the weight window, returning to step S1 after executing step S4 if it is determined that it is larger, and executing step S5 if it is determined that it is not larger, step S4 of splitting the particle and decreasing the weight, step S5 of determining whether to eliminate the particle, ending if it is determined that it is eliminated, and returning to step S1 after executing step S6 if it is determined that it is not eliminated, and step S6 of increasing the weight of the particle.

[0048] In one embodiment, the lattice spatial importance is obtained by solving the adjoint transport equation:

number

[0049] More specifically, the particles have a lattice space importance I n From the lattice of the lattice, the lattice space importance is I n+1 The motion is performed on the grid of I n+1 >I n If so, m = I n+1 / I n , split the particle into m particles, reduce the weight of each particle to 1 / m of the original weight, and n+1 n If so, we can play Russian roulette on the particles and get P=I n+1 / I n ​Then, sample a random number x between 0 and 1. If x is less than P, the particle survives and multiplies the weight by 1 / P; otherwise, extinguish the particle and end the simulation of the particle.

[0050] In another embodiment, the particle weight has an upper limit of 10 and a lower limit of 0.25; if the particle weight w is greater than 10, then the integer part of w is set to w1 and the decimal part is set to w2; sample a random number x from 0 to 1; if x is less than w2, then w=w1+1; if x is greater than w2, then w=w1; then split the particle into w particles and run the simulation until the weight of each particle drops to 1.

[0051] The radiation irradiation system and the control method thereof according to the embodiment of the present invention can reduce the calculation time by simulating particles through variance reduction, while ensuring the calculation accuracy.

[0052] A radiation irradiation system according to a ninth aspect of the present invention includes a beam irradiation device that generates a therapeutic beam and irradiates an irradiated body with the therapeutic beam to form an irradiated area, a treatment planning module that performs dose simulation calculations based on parameters of the therapeutic beam and medical image data of the irradiated area and creates a treatment plan, the treatment planning module performing the simulation calculations using a non-uniform grid, and a control module that controls irradiation of the beam irradiation device based on the treatment plan.

[0053] Furthermore, the treatment planning module sets the grid size of the critical region to be smaller than the grid size of the non-critical region.

[0054] Furthermore, the treatment planning module sets the grid size of the area where the tumor is located to 0.4 mm or less.

[0055] Additionally, the treatment planning module sets the grid size for blood, air and bone regions to 1.6 mm or greater.

[0056] Furthermore, the treatment planning module sets the grid size of the area where normal muscle is located to be greater than 0.8 mm and smaller than 1.6 mm.

[0057] The radiation irradiation system is preferably a neutron capture therapy system, and the beam irradiation device includes a neutron generator, a beam shaper and a treatment table, the neutron generator includes an accelerator and a target, the accelerator accelerates charged particles to generate a charged particle beam and interacts with the target to generate a neutron beam, the beam shaper is capable of adjusting the neutron beam generated by the neutron generator to a predetermined beam quality, and the neutron beam generated by the neutron generator passes through the beam shaper and is irradiated to an irradiated object on the treatment table.

[0058] A method for controlling a radiation irradiation system according to a tenth aspect of the present invention, comprising the steps of: Radiation irradiation system The radiation irradiation system includes a beam irradiation device that generates a treatment beam and irradiates an irradiated body with the treatment beam to form an irradiated area, a treatment planning module that performs dose simulation calculations based on parameters of the treatment beam and medical image data of the irradiated area and creates a treatment plan, and a control module that controls irradiation by the beam irradiation device based on the treatment plan, and the control method of the radiation irradiation system includes a step in which the treatment planning module performs simulation calculations using a non-uniform grid.

[0059] The control method further includes a step in which the treatment planning module sets a grid size of the critical region to be smaller than a grid size of the non-critical region.

[0060] The control method further includes a step in which the treatment planning module sets a grid size of the region where the tumor is located to 0.4 mm or less.

[0061] The control method further includes a step in which the treatment planning module sets the grid size in areas where blood, air, and bone are present to 1.6 mm or more, and sets the grid size in areas where normal muscle is present to greater than 0.8 mm and less than 1.6 mm.

[0062] The radiation irradiation system and control method thereof according to the embodiment of the present invention uses a non-uniform grid to perform simulation calculations, thereby improving the calculation accuracy of important regions, satisfying the calculation accuracy of non-important regions, and reducing the calculation time, without significantly increasing the calculation time. [Brief description of the drawings]

[0063] [Figure 1] FIG. 1 is a schematic diagram of a module of a boron neutron capture therapy system according to an embodiment of the present invention. [Diagram 2] 1 is a schematic diagram of a boron neutron capture therapy system according to an embodiment of the present invention. [Diagram 3] 1 is a flowchart of process parallelism and thread parallelism of a CPU in an embodiment of the present invention. [Figure 4] 1 is a flowchart of a simulation calculation using a GPU in an embodiment of the present invention. [Diagram 5] 1 is a flowchart for simulating particles using a variance reduction method in an embodiment of the present invention. [Figure 6] 1 is a flowchart of Russian roulette and splitting in an embodiment of the present invention. [Figure 7] 1 is a flowchart of implicit absorption in an embodiment of the present invention. [Figure 8] 1 is a flowchart of a wait window game in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] The embodiments of the present invention will be described in more detail below with reference to the drawings, so that those skilled in the art can practice the invention by referring to the specification.

[0065] Neutron capture therapy has been increasingly used in recent years as an effective means of cancer treatment, with boron neutron capture therapy becoming the most common. The neutrons used in boron neutron capture therapy can be supplied by nuclear reactors or accelerators. Boron neutron capture therapy (BNCT) is a method of ionizing boron ( 10 B) Utilizing the property that the contained drug has a large capture cross section for thermal neutrons, 10 B(n,α) 7 Li neutron capture and fission reactions 4 He and 7 The two heavy charged particles have an average energy of about 2.33 MeV and are characterized by a high linear energy transfer (LET) and a short range. The linear energy and range of the alpha particles are 150 KeV / μm and 8 μm, respectively. 7 In the case of Li heavy charged particles, the energy is 175KeV / μm and 5μm, respectively, and the total range of the two particles is about the size of a cell, so that the radiation damage to the living body is limited to the cellular level. The boron-containing drug can be selectively collected in tumor cells, and combined with a suitable neutron beam source, it can achieve the purpose of precisely killing tumor cells without causing significant damage to normal tissues.

[0066] Regardless of whether the neutron source of boron neutron capture therapy is nuclear reactor or nuclear reaction between charged particles and target, all of them generate mixed radiation field, that is, the beam contains neutrons and photons from low energy to high energy, and for boron neutron capture therapy of deep tumor, except epithermal neutrons, the higher the content of other radiation, the higher the proportion of non-selective dose deposition in normal tissue, so it is necessary to reduce these radiations that cause unnecessary dose deposition as much as possible. In order to further understand the quality factors of air beam as well as the dose distribution in human body by neutrons, the embodiment of the present invention uses the prosthesis of human head tissue to calculate the dose distribution, and the quality factors of the beam in the prosthesis are used as a reference for neutron beam design.

[0067] The International Atomic Energy Agency (IAEA) has put forward five proposals on the quality elements of air beams for neutron sources used in clinical boron neutron capture therapy, which can be used to compare the advantages and disadvantages of different neutron sources, and can also be used as a reference when selecting neutron generation pathways and designing beam shapers. The five proposals are as follows:

[0068] Epithermal neutron flux>1x10 9 n / cm 2 s Fast neutron contamination<2×10 -13 Gy-cm 2 / n Photon contamination<2×10 -13 Gy-cm 2 / n Thermal to epithermal neutron flux ratio<0.05 Epithermal neutron current to flux ratio>0.7 NOTE: The epithermal neutron energy region is from 0.5 eV to 40 KeV, the thermal neutron energy region is less than 0.5 eV, and the fast neutron energy region is greater than 40 KeV.

[0069] As shown in FIG. 1, the radiation irradiation system in this embodiment is a boron neutron capture therapy system 100, which includes a neutron beam irradiation device 10, a treatment plan module 20, and a control module 30. The neutron beam irradiation device 10 generates a therapeutic neutron beam N, and irradiates the therapeutic neutron beam N to an irradiated body 200 to form an irradiated part. The treatment plan module 20 performs a dose simulation calculation based on the parameters of the therapeutic neutron beam N generated by the neutron beam irradiation device 10 and medical image data of the irradiated part, and creates a treatment plan, and determines the position of the irradiated part relative to the neutron beam irradiation device 10 during irradiation treatment and the corresponding irradiation time based on the treatment plan. After the irradiated body 200 is positioned at the position determined based on the treatment plan, treatment can be started, and the control module 30 calls up the treatment plan corresponding to the current irradiated body 200 from the treatment plan module 20, and controls the irradiation of the neutron beam irradiation device 10 based on the treatment plan. The control module 30 may receive other data information, for example, data of the neutron beam irradiation device 10, data of the irradiation target 200, and the like.

[0070] As shown in FIG. 2, in this embodiment, the neutron beam irradiation device 10 includes a neutron generator 11, a beam shaper 12, a collimator 13, and a treatment table 14. The neutron generator 11 includes an accelerator 111 and a target T. The accelerator 111 accelerates charged particles (e.g., protons, deuterium nuclei, etc.) to generate a charged particle beam P such as a proton beam. The charged particle beam P is irradiated to the target T and interacts with the target T to generate a neutron beam (neutron beam) N. The target T is preferably a metal target. An appropriate nuclear reaction is selected depending on the required neutron yield and energy, the energy and current of the accelerated charged particles that can be provided, and the physical and chemical properties of the metal target. Commonly considered nuclear reactions are: 7 Li(p,n) 7 Be and 9 Be(p,n) 9B, and these two reactions are both endothermic reactions. The energy thresholds of the two nuclear reactions are 1.881 MeV and 2.055 MeV, respectively, and since the ideal neutron source for boron neutron capture therapy is epithermal neutrons at the keV energy level, theoretically, protons with an energy slightly higher than the threshold can be bombarded with a metallic lithium target to generate neutrons with relatively low energy, which can be used clinically without requiring too much deceleration processing, but the two targets, metallic lithium (Li) and metallic beryllium (Be), do not have a high cross section to interact with protons of the threshold energy, so in order to generate a sufficiently large neutron flux, protons with relatively high energy are generally selected to cause the nuclear reaction. An ideal target has characteristics such as high neutron yield, the energy distribution of the generated neutrons is close to the epithermal neutron energy region (described in detail below), does not generate a lot of radiation with strong penetrating power, is safe, inexpensive, easy to operate, and has high temperature resistance. However, it is impossible to find a nuclear reaction that satisfies all the requirements in practice, and a target made of lithium metal is used in the embodiment of the present invention. As is well known to those skilled in the art, the target T may be made of a metal material other than lithium and beryllium, for example, tantalum (Ta) or tungsten (W), and the target T may be disk-shaped or may have other solid shapes, or may use a liquid material (liquid metal). The accelerator 111 may be a linear accelerator, a cyclotron, a synchrotron, or a synchrocyclotron, and the neutron generator 11 may be a nuclear reactor without using an accelerator and a target. Regardless of whether the neutron source of boron neutron capture therapy is the nuclear reaction between charged particles and the target by nuclear reactor or accelerator, what is generated is actually a mixed radiation field, that is, the beam contains neutrons and photons from low energy to high energy. For boron neutron capture therapy of deep tumors, except for epithermal neutrons, the higher the content of other radiation, the higher the proportion of non-selective dose deposition in normal tissue, so it is necessary to reduce these unnecessary dose-causing radiation as much as possible.Also, it should be avoided to expose normal tissues of the subject to too much radiation, which would likewise cause unnecessary dose deposition.

[0071] The neutron beam N generated by the neutron generator 11 passes through the beam shaper 12 and the collimator 13 in order, and is irradiated to the subject 200 on the treatment couch 14. The beam shaper 12 can adjust the beam quality of the neutron beam N generated by the neutron generator 11, and the collimator 13 collects the neutron beam N and provides the neutron beam N with high targetability during treatment. As can be understood, the present invention may also be applied without a collimator, in which the beam is directly irradiated to the subject 200 on the treatment couch 14 after it leaves the beam shaper 12.

[0072] The beam shaper 12 further includes a reflector 121, a moderator 122, a thermal neutron absorber 123, a radiation shield 124 and a beam outlet 125. The energy spectrum of the neutrons generated by the neutron generator 11 is wide. In addition to the epithermal neutrons that meet the treatment needs, the content of other types of neutrons and photons must be reduced as much as possible to avoid causing damage to the operator or the irradiated body. Neutron Generator 11 The neutrons emitted from Reducer 122 Through this, the energy of fast neutrons (>40keV) must be adjusted to the epithermal neutron energy range (0.5eV~40keV), and epithermal neutrons (<0.5eV) must be reduced as much as possible. Reducer 122 The moderator 122 is made of a material that has a large cross section for interacting with fast neutrons and a small cross section for interacting with epithermal neutrons. In a preferred embodiment, the moderator 122 is made of D2O, AlF3, Fluental,The reflector 121 is made of at least one of CaF2, Li2CO3, MgF2 and Al2O3, and the reflector 121 surrounds the moderator 122 and reflects the neutrons that have passed through the moderator 122 and diffused to the surroundings into a neutron beam N to improve the utilization rate of neutrons, and is made of a material with high neutron reflection ability. In a preferred embodiment, the reflector 121 is made of at least one of Pb and Ni, and the moderator 122 has a thermal neutron absorber 123 at the rear and is made of a material with a large cross section that interacts with thermal neutrons. In a preferred embodiment, the thermal neutron absorber 123 is made of Li-6, and the neutrons that have passed through the moderator 122 are reflected into a neutron beam N to improve the utilization rate of neutrons. The thermal neutron absorber absorbs the thermal neutrons emitted from the neutron beam N, thereby reducing the content of thermal neutrons in the neutron beam N, and avoids giving too much dose to the superficial normal tissue during treatment. As can be understood, the thermal neutron absorber may be integrated with the moderator, and the material of the moderator includes Li-6, and the radiation shield 124 blocks neutrons and photons leaking from the portion other than the beam exit 125, and the material of the radiation shield 124 includes at least one of a photon shielding material and a neutron shielding material, and in a preferred embodiment, the material of the radiation shield 124 includes lead (Pb) as a photon shielding material and polyethylene (PE) as a neutron shielding material. The collimator 13 is installed behind the beam exit 125, and the epithermal neutron beam emitted from the collimator 13 is irradiated to the irradiated body 200, passes through the superficial normal tissue, and then is decelerated to thermal neutrons to reach the tumor cells M. As can be understood, Beam Shaper 12 may have another structure as long as it can obtain an epithermal neutron beam necessary for treatment, and for ease of explanation, when a collimator 13 is installed, the exit of the collimator 13 can be regarded as a beam exit 125 described later. In this embodiment, a radiation shielding device 15 is further installed between the irradiated body 200 and the beam exit 125 to shield the radiation of the beam exiting from the beam exit 125 against normal tissue of the irradiated body, and as can be understood, the radiation shielding device 15 does not have to be installed.

[0073] After the subject 200 takes or is injected with a boron (B-10)-containing drug, the boron-containing drug selectively accumulates in tumor cells M, and then, utilizing the property that the boron (B-10)-containing drug has a high capture cross section for thermal neutrons,10 B(n,α) 7 Li neutron capture and fission reactions 4 He and 7 The two charged particles have an average energy of about 2.33 MeV and are characterized by a high linear energy transfer (LET) and a short range. The linear energy transfer and range of the alpha particles are 150 keV / μm and 8 μm, respectively. 7 The linear energy deposition and range of Li heavy charged particles are 175 keV / μm and 5 μm, and the total range of the two types of particles is approximately equivalent to the size of a single cell. Therefore, the radiation damage to the living body is limited to the cellular level, and the goal of partially killing tumor cells can be achieved on the premise that no significant damage is caused to normal tissues.

[0074] The boron neutron capture therapy system 100 is entirely housed in a building of a concrete structure, and specifically, the boron neutron capture therapy system 100 further includes an irradiation room 101 and a charged particle beam generation room 102, and the irradiated subject 200 on the treatment table 14 is treated by irradiation with a neutron beam N in the irradiation room 101, and the charged particle beam generation room 102 at least partially houses the accelerator 111, and the beam shaper 12 is at least partially housed in a partition wall 103 between the irradiation room 101 and the charged particle beam generation room 102. As can be understood, the partition wall 103 may completely separate the irradiation room 101 and the charged particle beam generation room 102, or may partially separate the irradiation room 101 and the charged particle beam generation room 102, and the irradiation room 101 and the charged particle beam generation room 102 are in communication with each other. The number of targets T may be one or more, and the charged particle beam P selectively acts on one or some of the targets T or simultaneously acts on multiple targets T to generate one or more therapeutic neutron beams N. Depending on the number of targets T, the number of beam shapers 12, collimators 13, and treatment tables 14 may be one or more, and multiple treatment tables may be installed in the same irradiation room, or each treatment table may be installed in a separate irradiation room. The irradiation room 101 and the charged particle beam generation room 102 are spaces surrounded by concrete walls W (including a partition wall 103), and the concrete structure can block neutrons and other radiation leaked during the operation of the boron neutron capture therapy system 100.

[0075] In order to maximize the killing of cancer cells and reduce radiation damage to normal tissues, the accuracy of epithermal neutron and photon dose distribution is very important in the setting of the treatment planning module 20. In the application scene of the radiation irradiation system, the dose calculation is loaded into the photon and neutron cross section database, and the neutron cross section database is very large, so the installation of the software for creating the treatment plan of the radiation irradiation system occupies a large memory space, and when using the software to perform dose calculation simulation, the memory space occupied is large and the calculation time is long. The following embodiment of the present invention provides a series of optimization methods for the treatment planning module, which reduces the execution memory and reduces the dose calculation time to meet the demand for quickly creating a radiation treatment planning scheme. Each optimization method will be described below with reference to the drawings. EXAMPLES

[0076] The database is optimized in the treatment planning module 20 .

[0077] The human body contains more than 60 elements, of which more than 20 are essential elements and play an important role in maintaining the normal physiological functions of the human body. The elements with high content in the human body are carbon, hydrogen, oxygen, nitrogen, phosphorus, chlorine, sodium, magnesium, potassium, calcium, etc. Carbon, hydrogen, oxygen, and nitrogen are the main elements that compose the organic matter of the human body, accounting for 96% of the total weight of the human body, and the remaining abundant elements that account for more than 0.01% in the human body are calcium, potassium, phosphorus, sulfur, chlorine, magnesium, and sodium, respectively, accounting for 1.5%, 0.35%, 1%, 0.25%, 0.15%, 0.05%, and 0.15% of the total weight of the human body. From the above, the content of carbon, hydrogen, oxygen, nitrogen, calcium, potassium, phosphorus, sulfur, chlorine, magnesium, and sodium has reached 99.45% of the total weight of the human body, and the simulation and calculation system of more than 100 elements is stored in Monte Carlo. When using Monte Carlo for simulation and calculation every time, it takes a long time to simulate and calculate each element. In addition, the database of Monte Carlo is very large because the calculation and simulation system corresponding to many elements is stored. However, in the application scene of the radiation irradiation system, when simulating particles such as photons and neutrons in the human body using Monte Carlo, accurate calculation results can be obtained by only simulating elements in the human body that account for a large percentage (greater than 0.01%) of the total weight of the human body, and the simulation calculation of some trace elements takes a long time, and the difference value of the calculation result is within 0.001% compared with the result obtained by simulating elements that account for more than one ten-thousandth of the total weight of the human body.

[0078] In addition, some elements, such as Fe, have a large weight ratio in the human body, but do not react with neutrons and photons, or do not have a large reaction strength with neutrons and photons, so the impact of the simulation calculation results of such elements on the overall calculation results can be ignored.Some elements, such as boron, have a small weight ratio in the human body, but in the application scene of the radiation irradiation system, a large amount of boron medicine is injected into the human body and reacts strongly with neutrons, so they have a large impact on the final calculation results.

[0079] Taking into account the weight proportion of the elements in the human body and the reaction strength with neutrons and photons, elements (one or more elements selected from H, He, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, Ar, K and Ca) that have an influence on the simulation calculation results of neutrons and photons in the application scene of the radiation irradiation system are screened out, and only the screened elements are simulated in the simulation process, thereby reducing the simulation calculation time and improving the execution efficiency of Monte Carlo while ensuring the calculation accuracy. In addition, the database capacity corresponding to these screened elements is only 2% to 3% of the original database capacity, which significantly reduces the memory requirement for the magnetic disk and reduces the manufacturing cost.

[0080] On the one hand, in the neutron cross section database corresponding to each element, the Monte Carlo system stores cross section data corresponding to many temperatures, for example, 0K, 1200K, 2500K, 250K, 294K, 600K, 900K, for selection, but in the application scene of the radiation irradiation system, it is only necessary to perform simulation calculations on the human body model, and the normal temperature of the human body is 310K-315K. Based on the execution principle of Monte Carlo, after the temperature is input, the system automatically matches the temperature closest to the input temperature in many stored temperatures, and uses the temperature as a simulation parameter to perform simulation calculations, so after the temperature of the human body is input, the system matches the temperature 294K stored in the database, and uses 294K as a parameter to perform simulation calculations. In addition, the temperature used when calculating the Doppler effect is 0K. In other words, in application scenes of the radiation irradiation system, only two of the temperatures stored in the database, 294K and 0K, are used, and the other temperatures are unnecessary for the application scenes of the radiation irradiation system. Therefore, the database corresponding to temperatures other than 294K and 0K is removed, and the size of the database is reduced to about one-third of the original size, provided that it does not affect the simulation calculation structure, and the cost of running the database is reduced.

[0081] Table 1 shows the results of neutron dose simulation calculations performed on the same human body model by the Monte Carlo system at temperatures of 294K, 310K, and 330K, respectively.

[0082] [Table 1]

[0083] As can be seen from the data in Table 1, the impact of small temperature fluctuations on the final calculation result of neutron dose can be ignored, and in the application scenario of the radiation irradiation system, the usage requirements can be met by simply retaining the database corresponding to 294K stored in the system, and the error of the final calculation result is within the acceptable range. EXAMPLES

[0084] During the particle simulation, the process is blocked to reduce the particle simulation time.

[0085] In the application scene of the radiation irradiation system, the dose calculation includes neutron dose calculation and photon dose calculation. In the process of photon movement in the body of the irradiated subject, the photon energy and the half-absorption thickness of the photon gradually decrease, but the absorption cross section of the photon increases rapidly with the decrease of the photon energy and the half-absorption thickness of the photon. When the half-absorption thickness of the photon is smaller than the size of a cell, the probability that the photon is absorbed in the cell where it is located is very large. In this case, the photon is directly set to deposit all the energy in the cell where it is located, and the simulation is not continued, and the error between the dose distribution calculated after such processing and the dose distribution calculated by continuing the simulation of the photon is within 0.1%.

[0086] If the size of a human cell is 2-200 μm, and the minimum dimension of the model lattice is usually 0.8 mm in the application of a radiation irradiation system, the simulation of the photon can be stopped when the half-absorption thickness of the photon is smaller than one-quarter of the minimum dimension of the lattice.

[0087] Specifically, calculate the half-absorption thickness t of the photon using equation (1-1),

number

[0088] In the following, the half-absorption thickness of the skeleton of the human body is calculated for different photon energy values.

[0089] [Table 2]

[0090] As can be seen from Table 2, in the skeleton, when the photon energy is less than 10 KeV, the half-absorption thickness of the photon is less than 0.2 mm, that is, when the photon energy is less than 10 KeV, there is a very large possibility that the photon will be absorbed in the lattice where it is currently located, so in this case, the difference between the dose obtained by stopping the photon simulation and the dose obtained by further simulating the photon is within an acceptable range.

[0091] Since the half-absorption thickness of photons in cell tissue is determined by the material through which the photons pass and the photon energy, cutoff energies corresponding to various materials can be set, and when the photon energy is lower than the cutoff energy, the photon simulation can be stopped. Hereinafter, a simulation calculation is performed in a human body model to obtain photon doses corresponding to different set photon cutoff energies.

[0092] [Table 3]

[0093] Table 3 As can be seen, when the photon energy is 10 KeV or less, the error between the final photon dose calculated by stopping the photon simulation calculation and the dose distribution obtained by continuing the photon simulation calculation is within 0.1%.

[0094] From the above, in the process of photon simulation calculation, if the photon energy is smaller than a certain cutoff energy, the half-absorption thickness of the photon is smaller than the size of one cell. In this case, the photon simulation is stopped, and the calculation time of the photon dose can be reduced without affecting the calculation result of the dose distribution.

[0095] In another embodiment, the first predetermined value and the second predetermined value are set according to the requirements of actual simulation accuracy, and when the half-absorption thickness of the photon is equal to or less than the first predetermined value, or when the photon energy is equal to or less than the second predetermined value, the photon simulation is stopped, the first predetermined value may be larger than the size of a cell, or may be smaller than the size of a cell, and the second predetermined value may be 12 KeV, 16 KeV, etc. EXAMPLES

[0096] Parallel techniques are used to accelerate the dose calculation module.

[0097] The treatment planning module of the radiation irradiation system uses the Monte Carlo method, and the simulation processes of different source particles are completely independent, that is, the simulation order of different particles does not affect the calculation result. Based on this calculation characteristic, the simulation tasks of different source particles are assigned to different processes or threads, and the calculation tasks of each process or thread are completed and then combined to obtain the final calculation result. The computer can provide two types of parallelism, namely CPU process parallelism and thread parallelism, and GPU acceleration.

[0098] As shown in Fig. 3, the so-called process-parallel and thread-parallel calculation process of CPU includes the steps of firstly obtaining the number of processes or threads and obtaining a value n, then dividing the particles to be simulated into n evenly, then simulating and counting one particle in each thread or process independently, and finally, collating the counts obtained in each process or thread to obtain a final dose. By allocating particles to different processes or threads and simulating and calculating, the simulation and calculation time is reduced to 1 / n (process) or 1 / 2n of the time required to simulate and calculate all particles using one process or thread.

[0099] Both process parallelism and thread parallelism use multi-core CPUs to achieve parallel calculations, and GPU acceleration is achieved by the parallel calculations of the multi-core processors of GPUs. The effect of process and thread parallelism is limited by the cost of the CPU, and in a typical standalone case, the number of cores is four. Thus, process parallelism and thread parallelism can increase the speed by up to four times (process) or eight times (thread). One GPU integrates multiple processors, and theoretically the calculation speed can be increased by several times.

[0100] As shown in FIG. 4, the so-called GPU-accelerated simulation calculation process includes the steps of firstly, the system transfers random numbers, cross-sectional area data, etc. from CPU memory to GPU graphic memory, then, each processor in the GPU simulates, calculates, and counts a single particle, and stats the counting result into a global count; and then, the system judges whether there are any unsimulated particles, and if there are no unsimulated particles, transfers the counting result from GPU memory to CPU memory; if there are unsimulated particles, returns to the previous step and continues to simulate and count the unsimulated particles until the simulation of all particles is completed.

[0101] Since the GPU has many processors, the simulation calculation accelerated by the GPU can greatly improve the calculation speed and reduce the calculation time. In addition, the CPU uses an Intel Xeon processor with 2.27GHz, which costs about 6000 RMB, and the GPU uses an NVIDIA Tesla C2050, which costs about 9000 RMB. Each GPU has a total of 448 processors, which are equivalent to 448 CPUs. The calculation time of the CPU is 50 to 70 times that of the GPU. As a result, the simulation calculation using the GPU has a great advantage in terms of price and time required, compared to the CPU. EXAMPLES

[0102] A Monte Carlo variance reduction method is used to speed up and converge.

[0103] The Monte Carlo method has a wealth of variance reduction methods to improve the calculation speed of the program. The variance reduction methods that can be used in the treatment planning system include implicit absorption, weight window game, Russian roulette and splitting, etc., and Russian roulette and splitting are composed of Russian roulette method and splitting method. Below, we will explain the Russian roulette method, splitting method, lattice space importance, implicit absorption and weight window game of the variance reduction method.

[0104] For the Russian roulette method, typically the weight of a particle is set with an upper bound of 10 and a lower bound of 0.25. If the weight w of a particle drops below some predefined value (e.g., 0.25), we sample a random number x from 0 to 1; if x is less than w, the particle survives and the weight of the particle returns to 1; if x is greater than or equal to w, we annihilate the particle and end the simulation of the particle.

[0105] For the splitting method, if the weight w of a particle is greater than a certain value (e.g., 10), set the integer part of w to w1 and the decimal part to w2, sample one random number x from 0 to 1, and if x is less than w2, set w=w1+1, and if x is greater than w2, set w=w1. Then, split one particle into w particles and run the simulation until the weight of each particle drops to 1.

[0106] Regarding lattice spatial importance, the dose contributions of particles in different regions of the model are different, and the spatial importance represents the dose contributions of particles. Before the simulation, the lattice spatial importance of each lattice is calculated based on parameters such as the tumor location and model characteristics. A particle is assigned a lattice spatial importance of I n From the lattice of the lattice, the lattice space importance is I n+1 Move to the grid of I n+1 >In If so, m = I n+1 / I n Then, we split the particle into m particles, reduce the weight of each particle to 1 / m of the original, and n+1 n If so, we can play Russian roulette on the particles and get P=I n+1 / I n Then, sample a random number x between 0 and 1. If x is less than P, the particle survives and multiplies the weight by 1 / P; otherwise, extinguish the particle and end the simulation of the particle.

[0107] Regarding the calculation method of the lattice space importance, the lattice space importance is obtained by calculating the adjoint flux, and the adjoint flux is obtained by solving the adjoint transport equation of the following formula:

number

[0108] For implicit absorption, when a particle interacts with a substance, the particle can only be scattered and not absorbed, and the particle weight is increased by P 散乱 / P 総 If the weight of a particle drops to a certain value (say 0.25), we use the Russian roulette method to process the particle.

[0109] For the weight window game, if the particle weight is greater than a certain value, e.g., 10, a splitting approach is performed, and if the particle weight is less than a certain value, e.g., 0.25, a Russian roulette approach is performed. The two values ​​here are set based on the software performance. ​

[0110] In summary, when a particle moves from a place with low lattice spatial importance to a place with high lattice spatial importance, the particle weight is improved, and when the particle does not disappear but the weight is reduced, when the particle moves from a place with high lattice spatial importance to a place with low lattice spatial importance, the particle weight is reduced, and splitting or implicit absorption processing is performed on the particle. Since the absorption cross section of thermal neutrons in the human body (mainly elements such as N and B) is large, in order to accelerate the dose calculation convergence speed of lattices away from the neutron source, the particle should move to these lattices by implicit absorption. When a particle leaves the treatment area, continuing the simulation of the particle is not very meaningful for the dose calculation in the treatment area, and in this case, continuing the calculation will waste calculation resources, so by setting the lattice spatial importance, the occurrence probability of such a situation can be reduced. If the particle weight is too small, the contribution of the particle count is very small, and continuing the simulation will waste computational resources; if the particle weight is too large, it will cause a single count to be too large, and there is a risk of incorrect results, so the weight window should be set to make the particle weight in a suitable range. Therefore, in combination with implicit absorption, it is necessary to accelerate the convergence speed of the Monte Carlo program by reasonably setting the lattice space importance and the weight window game.

[0111] As shown in FIG. 5, the flow of simulating particles using the variance reduction method includes step S1 of acquiring one source particle, step S2 of judging whether the particles will collide within a lattice cell, and if it is judged that they will collide, steps S3 and S4 are executed in order, and if it is judged that they will not collide, steps S5 and S6 are executed in order, step S3 of performing implicit absorption processing, step S4 of judging whether the weight is lower than the weight window, and if it is judged to be lower, step S7 is executed, and if it is judged to be not lower, step S5 of returning to step S2, step S5 of performing Russian roulette and splitting processing, and step S6 of performing Russian roulette and splitting processing. Step S6: determining whether to perform Russian roulette processing, and if it is determined that Russian roulette processing is to be performed, executing step S7, and if it is determined that Russian roulette processing is not to be performed, returning to step S2; step S7: determining whether to annihilate, and if it is determined that to annihilate, executing step S8, and if it is determined that to not annihilate, executing step S9 and then returning to step S2; step S8: determining whether the processing of the particle is completed, and if it is determined that it is completed, ending the flow, and if it is determined that it is not completed, returning to step S1; and step S9: dividing the weight by the annihilation probability.

[0112] As shown in FIG. 6, the flow of Russian roulette and splitting includes step S1 of calculating and recording the lattice space importance of each lattice, step S2 of acquiring particles, step S3 of performing weight window detection and operation on the particles, and step S4 of calculating the lattice space importance I before and after the particle crosses the lattice boundary. n and I n+1 Step S4 of calculating I n I n+1The method includes step S5 of comparing whether the particle is greater than the weighted particle, and if it is not greater, executing step S6 and then returning to step S3, and if it is greater, executing step S7; step S6 of splitting the particle and decreasing the weight of the particle; step S7 of determining whether to annihilate the particle, and if it is determined that the particle should be annihilated, executing step S9, and if it is determined that the particle should not be annihilated, executing step S8 and then returning to step S3; step S8 of increasing the weight of the particle; and step S9 of determining whether the simulation of the particle is completed, and if it is determined that the simulation is not completed, returning to step S2, and if it is determined that the simulation is completed, terminating.

[0113] As shown in FIG. 7, the flow of implicit absorption includes step S1 of acquiring particles, step S2 of determining whether the particles will collide within a lattice cell, and if it is determined that the particles will collide, executing step S3, and if it is determined that the particles will not collide, returning to step S1, step S3 of multiplying the weight by the scattering occurrence probability, step S4 of determining whether the weight of the particle is smaller than the lowest weight, and if it is determined that the weight is smaller, executing step S5, and if it is determined that the weight is not smaller, returning to step S2, step S5 of determining whether the particle is to be annihilated, and if it is determined that the particle is to be annihilated, executing step S7, and if it is determined that the particle is not to be annihilated, returning to step S2 after executing step S6, step S6 of dividing the weight by the annihilation probability, and step S7 of determining whether the simulation of the particle is completed, and if it is determined that the simulation is not completed, returning to step S1, and if it is determined that the simulation is completed, terminating the process.

[0114] As shown in FIG. 8, the flow of the weight window game includes step S1 of simulating particle movement, step S2 of determining whether the weight of the particle is within the weight window range, returning to step S1 if it is determined that it is within the range, and executing step S3 if it is determined that it is not within the range, step S3 of determining whether the weight is larger than the weight window, returning to step S1 after executing step S4 if it is determined that it is larger, and executing step S5 if it is determined that it is not larger, step S4 of splitting the particle and decreasing the weight, step S5 of determining whether to eliminate the particle, ending if it is determined that it is eliminated, and returning to step S1 after executing step S6 if it is determined that it is not eliminated, and step S6 of increasing the weight of the particle.

[0115] To compare the acceleration effect of the variance reduction method on dose calculation, the calculation time and the standard deviation of the results are compared between when implicit absorption is used and when implicit absorption is not used. For the same human body model, 10 million particles are calculated, and the calculation time when the implicit absorption method is used is 1584 s, and the standard deviation of the dose calculation is 11%, while the calculation time when the implicit absorption method is not used is 1258 s, and the standard deviation of the dose calculation is 14.5%. In order to reduce the standard deviation to the same as that when the implicit absorption method is used, it is necessary to increase the number of simulated particles to 16 million and increase the simulation calculation time to 2045 s, which is 461 s more than the calculation time when the implicit absorption method is used, that is, the calculation time is reduced by about 20% when the implicit absorption method is used. EXAMPLES

[0116] Simulation calculations are performed using a non-uniform rectangular grid.

[0117] Conventional human body model calculations often use uniform grids, and in some cases, the number of grids must be increased for precise calculation of partial regions, which results in longer calculation times and exponential increases in running memory. Models read from CT or PET are often obtained with uniform grids, and the materials of many connected regions are the same, such as air, blood, etc., and for some of these regions, there is no need to accurately calculate fine dose distribution, so a coarse grid can replace a fine grid, and for important locations such as tumors, a finer grid must be separated to achieve more precise calculations. By using non-uniform grids to calculate doses, calculation accuracy can be improved, and calculation time and running memory do not increase significantly, and calculation accuracy of important regions can be improved when calculation time is not significantly increased, and calculation time can be reduced when calculation accuracy of non-important regions is met.

[0118] Below, simulation calculations are performed by setting grids of different dimensions, and the effects of different grid dimensions on simulation time and calculation accuracy are compared.

[0119] [Table 4]

[0120] In this experiment, the mixed grid used was in the direction of neutron incidence, with the first 5 cm section consisting of a 0.4 mm grid, the middle 5 cm section consisting of a 0.8 mm grid, and the remaining section consisting of a 1.6 mm grid. As can be seen from Table 3, by using a non-uniform grid, the total number of grids was reduced to 2 / 5 of the original number of 0.4 mm grids, the memory required for the grids was also reduced to 1 / 3 of the original, and the calculation time was reduced to 34.7% of the original. Compared to the results obtained by calculation using a 0.4 mm grid, the neutron error in the results obtained by calculation using a mixed grid was less than 0.1%, and the photon error was less than 0.2%.

[0121] The configuration pattern of the mixed lattice is not limited to the above-mentioned patterns, and can be set according to the specific situation of the irradiated body.In general, the size of the lattice is determined according to the importance of the region, for example, the size of the lattice of the region where the tumor is located is set to be small, 4mm or less, the size of the lattice of the region where blood, air and bone are located is set to be large, 1.6mm or more, and the size of the lattice of the region where other normal muscle and other tissues are located is set to be larger than 0.8mm and smaller than 1.6mm.

[0122] The algorithm used for dose calculation is the Monte Carlo algorithm, which has the advantage of high calculation accuracy and the disadvantage of slow convergence speed and long calculation time, so optimization of calculation efficiency is the most important part. The optimization methods of Examples 1 to 5 of the present application can improve calculation efficiency and reduce calculation time to different degrees.

[0123] The above describes exemplary specific embodiments of the present invention to facilitate understanding of the present invention for those skilled in the art. However, it is obvious that the present invention is not limited to the scope of the specific embodiments. Various changes are obvious to those skilled in the art, and are all within the scope of the claims of the present invention, provided that they are within the spirit and scope of the present invention as defined and determined by the appended claims.

Claims

1. a beam irradiation device that generates a treatment beam and irradiates an irradiation target with the treatment beam to form an irradiation site; a treatment planning module that performs a dose simulation calculation based on the parameters of the treatment beam and the medical image data of the irradiated area, and creates a treatment plan, the treatment planning module stopping a simulation for photons when a half absorption depth of the photons is equal to or less than a first predetermined value; a control module for controlling irradiation of the beam irradiation device based on the treatment plan; Characterized in that it comprises Radiation exposure system.

2. Neutron capture therapy system, The beam irradiation device includes a neutron generator, a beam shaper, and a treatment table; The neutron generator includes an accelerator and a target; the accelerator accelerates charged particles to generate a charged particle beam and interacts with the target to generate a neutron beam; The beam shaper is capable of adjusting the neutron beam generated by the neutron generator to a predetermined beam quality, The neutron beam generated by the neutron generator passes through the beam shaping body and is irradiated to the subject on the treatment table. The radiation delivery system of claim 1 .

3. The treatment planning module calculates the half-absorption thickness t of the photon by the formula (1-1), [0010] where μ is the linear attenuation coefficient of the photon, which is determined by the material through which the photon passes and the photon energy. The radiation delivery system of claim 1 .

4. the first predetermined value is the size of a single cell; The first predetermined value is 0.2 mm; when the photon energy is less than or equal to a second predetermined value, the photon half absorption thickness corresponding to the photon energy is less than or equal to a first predetermined value; The second predetermined value is 10 KeV. The radiation delivery system of claim 1 .

5. A method for controlling a radiation irradiation system, comprising: The radiation irradiation system includes: a beam irradiation device that generates a treatment beam and irradiates an irradiation target with the treatment beam to form an irradiation site; a treatment planning module that performs a dose simulation calculation based on the parameters of the treatment beam and the medical image data of the irradiated area, and creates a treatment plan; a control module for controlling irradiation of the beam irradiation device based on the treatment plan; Including, The treatment planning module stops simulating the photon if the half absorption thickness of the photon is less than or equal to a first predetermined value. A method for controlling a radiation irradiation system.

6. The treatment planning module calculates the half-absorption thickness t of the photon by the formula (1-1), [0025] where μ is the linear attenuation coefficient of the photon, which is determined by the material through which the photon passes and the photon energy. The method for controlling the radiation irradiation system according to claim 5 .

7. The first predetermined value is the size of a single cell. The method for controlling the radiation irradiation system according to claim 6.

8. The first predetermined value is 0.2 mm. The method for controlling the radiation irradiation system according to claim 6.

9. When the photon energy is equal to or less than a second predetermined value, the half absorption thickness of the photon corresponding to the photon energy is equal to or less than a first predetermined value. The method for controlling the radiation irradiation system according to claim 5 .

10. The second predetermined value is 10 KeV. The method for controlling a radiation irradiation system according to claim 9.

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