A design method for radiation source equalizer based on Monte Carlo simulation

Abstract

The present invention belongs to the field of radiation technology and biological irradiation technology, and discloses a method for designing a radiation source homogenizer based on Monte Carlo simulation, comprising the following steps: S1, establishing a Monte Carlo simulation model; S2, setting digital model input parameters; S3, performing Monte Carlo simulation, obtaining the dose distribution of a plane position at a certain depth below the surface of a water phantom, judging the dose distribution result, and entering S5 if the homogenization requirement is met, otherwise entering S4; S4, adjusting the homogenizer design parameters based on the simulated dose distribution, and then returning to S3; S5, making a homogenizer, performing dose measurement and judging the dose distribution result: entering S7 if the homogenization requirement is met, otherwise entering S6; S6, after adjusting based on the current homogenizer design parameters, returning to S3; S7, completing the homogenizer design. The present invention can improve the design efficiency and homogenization effect of the homogenizer, reduce the design cost, and improve the adaptability of the homogenizer to different radiation sources.

Description

Technical Field

[0001] The invention belongs to the field of radiation technology and biological irradiation technology, and in particular relates to a radiation source homogenizer design method based on Monte Carlo simulation. Background Art

[0002] The development of nuclear technology has greatly promoted the progress of human society. For example, radiological diagnosis and treatment applied in the medical field have improved human health, and nuclear energy applied in the energy field has alleviated the current energy crisis. The application of nuclear technology depends on the understanding of the characteristics of various radiation particles, which is essentially the control of radiation. Therefore, the accurate understanding of the particle transport process is directly related to the application level of nuclear technology, from the atomic bomb technology of uncontrolled nuclear fission to the reactor nuclear power plant technology that controls the fission reaction rate; from the early close-range radiotherapy of tumors with radium tubes to the current use of electronic linear accelerators to achieve intensity-controlled and field-controlled precision radiotherapy, heavy ion and boron neutron capture therapy, etc., all reflect the progress of human mastery of nuclear technology.

[0003] At present, medical linear accelerators usually use X-rays with energy of 4-20MeV as the irradiation source, and use electron beam target shooting to generate X-ray beams. However, the dose distribution of the X-ray beam generated by electron beam target shooting is not uniform. In actual use, the radiation source (such as medical accelerator, X-ray tube, isotope radiation source, etc.) needs to be corrected by a leveler so that it can obtain a dose distribution of 35-40cm in size at the treatment site and meet certain flatness and symmetry requirements before it can be used for clinical treatment. Since the attenuation degree of rays of various energies is different when passing through different materials, the probability of interactions such as photoelectric effect, Compton effect or electron pair effect is different. The material selection of the leveler and the setting of geometric parameters have become a problem worth studying at present.

[0004] At present, the structure of the leveler is mostly conical or multi-stage frustum, which requires repeated modification of the structure of the leveler and multiple tests and measurements to achieve the leveling effect. This method is not only time-consuming and costly, but also often has a poor leveling effect. At the same time, the applicability of the leveler with multi-stage frustum stacking is poor and cannot meet the actual use requirements of different radiation sources. Summary of the invention

[0005] The present invention aims to address the technical problems existing in the background technology and provide a radiation source equalizer design method based on Monte Carlo simulation, so as to improve the design efficiency of the equalizer, reduce the design cost, and improve the equalization effect. The equalizer structure design is guided according to the isodose line diagram, so that the equalizer structure is no longer limited to the traditional cone or multi-stage cone shape, thereby improving the adaptability of the equalizer to different radiation sources.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A method for designing a radiation source equalizer based on Monte Carlo simulation comprises the following steps:

[0008] S1. Establishing a Monte Carlo simulation model: establishing digital models of corresponding radiation sources, homogenizers and water phantoms (i.e., water phantoms, water phantom bodies, uniform water phantom bodies, etc., which are models established in Monte Carlo simulations with the same radiation characteristics as water, for the purpose of simulating dose measurements) based on Monte Carlo simulation;

[0009] S2. Setting digital model input parameters: input parameters according to actual needs and initialize the digital models of the radiation source, homogenizer and water phantom;

[0010] S3, perform Monte Carlo simulation: perform Monte Carlo simulation based on the established digital model, obtain the dose distribution at a plane position at a certain depth below the surface of the water phantom, and judge the dose distribution result. If it meets the uniformity requirement, proceed to S5, otherwise proceed to S4;

[0011] S4, simulation iterative optimization of design parameters: adjust the uniformizer design parameters based on the simulated dose distribution, and then return to S3;

[0012] S5. Make a homogenizer, perform dose measurement and judgment: make a homogenizer according to the homogenizer design parameters that meet the homogenization requirements in S3, and load it on the corresponding radiation source to perform dose measurement;

[0013] Determine the dose distribution result: if it meets the uniformity requirement, go to S7, otherwise go to S6;

[0014] S6, measuring and iterating the optimization design parameters: after making adjustments based on the current equalizer design parameters, return to S3;

[0015] S7. Complete the design of the equalizer: obtain a equalizer that meets the equalization requirements of the corresponding radiation source.

[0016] Furthermore, in S1, the radiation source includes any one of a medical accelerator, an X-ray tube or an isotope radiation source.

[0017] Furthermore, in said S1, a medical accelerator is used as a radiation source to construct a digital model of the radiation source;

[0018] The digital model of the radiation source includes, from top to bottom, an electron beam, a target, a primary collimator, a homogenizer, an ionization chamber, a mirror, a secondary collimator and a water phantom.

[0019] Furthermore, in S2, the digital model input parameters at least include: radiation source parameters, uniformizer geometric parameters and materials, and the distance between the water phantom and the radiation source.

[0020] Furthermore, in S3, when the Monte Carlo simulation is performed for the first time, the leveler is initially set to a flat plate structure.

[0021] Further, in S4, the method for adjusting the design parameters of the leveler is:

[0022] Draw an isodose line map according to the dose distribution, project the isodose line map onto the surface of the equalizer, partition the surface of the equalizer according to the isodose line map, set the thickness of each partition area according to the dose level, and the thickness of the high-dose area is greater than the thickness of the low-dose area.

[0023] Furthermore, in S4, the method for setting the thickness of adjacent dose partitions on the equalizer adopts an ellipsoid fitting method.

[0024] Furthermore, in S5, the method for manufacturing the equalizer includes precision machining or 3D printing.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] (1) The present invention designs a uniformizer for a radiation source based on Monte Carlo simulation. By using Monte Carlo simulation to perform iterative optimization, the time spent on optimizing the design parameters of the uniformizer is significantly shortened, the design efficiency of the uniformizer is greatly improved, and the trial and error cost is reduced. At the same time, the invention also performs iterative optimization based on the results of actual experimental measurements after manufacturing the uniformizer, thereby avoiding the situation where the simulation results are inconsistent with the uniformization effect during actual use, and ensuring the uniformization effect of the simulated design parameters in actual scenarios. The entire design process is carried out through two iterative optimization methods (simulation iterative optimization + measurement iterative optimization) to make up for each other's shortcomings, and the uniformizer structure design parameters are guided according to the isodose line diagram, so that the uniformizer structure is no longer limited to the traditional cone or multi-stage cone shape, thereby improving the adaptability of the uniformizer to different radiation sources. The invention is extremely practical and economical, and is worthy of promotion.

[0027] (2) When guiding the design parameters of the equalizer structure according to the isodose line map, the present invention obtains the dose distribution through Monte Carlo simulation, draws the isodose line map according to the simulated dose distribution and projects it onto the surface of the equalizer, divides the area according to the isodose line map, and assigns a thickness value to each partition area according to the dose level. The thickness of the high-dose area is greater than the thickness of the low-dose area. By adopting the above method, the various design parameters of the entire equalizer can be determined through a single Monte Carlo simulation. The design method is simple and efficient, and the entire design cycle is significantly shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flow chart of the method of the present invention;

[0029] Figure 2Schematic diagram of the structure of a radiation source model according to an embodiment of the present invention;

[0030] Figure 3 This is a dose distribution diagram at 10 cm below the water phantom when there is no homogenizer in an embodiment of the present invention;

[0031] Figure 4 This is a dose distribution diagram at 10 cm below the water model when the initial homogenizer is loaded according to an embodiment of the present invention;

[0032] Figure 5 This is a dose distribution diagram at 10 cm below the surface of the equivalent water phantom when the homogenizer is loaded after the first simulation iteration optimization according to an embodiment of the present invention;

[0033] Figure 6 This is a dose distribution diagram at 10 cm below the surface of the equivalent water phantom when the homogenizer is loaded with iterative optimization according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The embodiment of the present invention provides a method for designing a radiation source homogenizer based on Monte Carlo simulation, such as Figure 1 As shown, the method comprises the following steps:

[0036] S1. Establishing Monte Carlo simulation model: Based on Monte Carlo simulation, establish digital models of corresponding radiation source, homogenizer and water phantom (i.e. water phantom, water phantom body, uniform water phantom body, etc., which are models established in Monte Carlo simulation with the same radiation characteristics as water, for the purpose of simulating dose measurement).

[0037] It can be understood that the construction of the digital model of the radiation source is based on the Monte Carlo simulation software, and different digital models of the radiation source can be simulated and constructed according to the actual situation.

[0038] As a preferred embodiment, in S1, the radiation source includes but is not limited to one of a medical accelerator, an X-ray tube and an isotope radiation source.

[0039] For example, in this embodiment, a medical accelerator is used as a radiation source, and a medical accelerator digital model is constructed as a radiation source digital model. Figure 2As shown, the digital model of the radiation source includes an electron beam, a target, a primary collimator, a homogenizer, an ionization chamber, a mirror, a secondary collimator and a water phantom from top to bottom. In the digital model of the radiation source, from top to bottom, the electron beam is first incident vertically to hit the target, and the generated beam is collimated by the primary collimator and then irradiated on the homogenizer. At this time, the homogenizer is an initialized homogenizer structure, and its upper end surface is overall flat. The beam then passes through the ionization chamber, the mirror and the secondary collimator, and finally irradiates on the water phantom. By constructing a digital model of a medical accelerator, medical accelerators with various parameters can be simulated;

[0040] S2. Setting digital model input parameters: Input parameters according to actual needs to initialize the digital models of the radiation source, homogenizer and water phantom.

[0041] As a preferred embodiment, in S2, the digital model input parameters include but are not limited to: radiation source parameters, uniformizer geometric parameters and materials, and the distance between the water phantom and the radiation source.

[0042] Exemplarily, in this embodiment, the digital model input parameters include but are not limited to: energy and radius of the electron beam, geometric parameters and materials of the target, given parameters of the primary collimator and the secondary collimator, initial design parameters of the uniformizer, etc.

[0043] When performing simulation, the parameters of the digital model can be adjusted according to the parameters of the medical accelerator. For example, the electron beam energy is set to 16 MeV, the radius is 0.001 cm, the target is set to a rectangular structure with a size of 2.0 cm × 2.0 cm × 3.0 cm, the number of simulated particles is set to 107, the SSD is set to 50 cm, the field is 10.0 cm × 10.0 cm, and the homogenizer is initially set to a square aluminum plate with a thickness of 2 mm and a length of 5.0 cm;

[0044] S3, perform Monte Carlo simulation: perform Monte Carlo simulation based on the established digital model, obtain the dose distribution at a plane position at a certain depth below the surface of the water phantom, and judge the dose distribution result. If it meets the uniformity requirement, enter S5, otherwise enter S4.

[0045] As a preferred embodiment, in S3, when the Monte Carlo simulation is performed for the first time, the homogenizer is initially set to a flat plate structure. In the initial state of the homogenizer, the dose distribution at a plane position 10 cm below the surface of the water phantom is simulated and measured, and the isodose lines are drawn as follows: Figure 4 shown and can be used with Figure 3 The dose distribution diagram at 10 cm below the water phantom without a homogenizer is compared with the simulated dose distribution results to determine whether it is necessary to iteratively optimize the homogenizer design parameters; since the design parameters of the homogenizer are initial values ​​when the simulation is performed for the first time, its flat plate structure makes the homogenization effect poor, so the image Figure 4 The same dose distribution results can be seen. Figure 3 In comparison, Figure 4 There is only a small attenuation of the dose, and the uniformity effect is not achieved. Therefore, the first simulation will enter S4 for simulation iteration to optimize the design parameters. In the subsequent process, as the number of simulation iterations increases, the simulation results will be continuously optimized, and eventually the uniformity requirements will be met and enter S5.

[0046] S4. Simulate iterative optimization of design parameters: adjust the uniformizer design parameters based on the simulated dose distribution, and then return to S3.

[0047] In S4, the method for adjusting the design parameters of the equalizer is: drawing an isodose line map according to the dose distribution, projecting the isodose line map onto the surface of the equalizer, partitioning the surface of the equalizer according to the isodose line map, and setting the thickness of each partition area according to the dose level, so that the thickness of the high-dose area is greater than the thickness of the low-dose area.

[0048] Among them, after projecting the isodose line map onto the surface of the equalizer, the thickness of the area divided by the isodose line is assigned. The higher the dose, the higher the thickness value is, that is, the thickness of the equalizer at this position is greater. Similarly, the lower the dose, the lower the thickness value is, that is, the thickness of the equalizer at this position is smaller. At this time, the design parameters of the equalizer with different thickness distributions can be obtained.

[0049] For example, an isodose line diagram can be drawn according to the percentage based on the dose distribution, and the end face of the equalizer can be divided into multiple areas. The thickness of the area with the highest dose is assigned to 100%, the thickness of the adjacent area is assigned to 90%, and so on, so as to obtain the thickness distribution of the entire equalizer. Based on the above design parameters, return to S3 and re-perform the Monte Carlo simulation.

[0050] As a preferred embodiment, in S4, the setting method for assigning thickness values ​​to adjacent dose partitions on the equalizer adopts, but is not limited to, an ellipsoid fitting method. Exemplarily, the dose distribution parameters are converted into three-dimensional parameters of the ellipsoid by fitting, and the parameters are finally used as the equalizer design parameters under the current simulation;

[0051] S5. Make a homogenizer, measure the dose and make a judgment: make a homogenizer according to the homogenizer design parameters that meet the homogenization requirements in S3, and load it on the corresponding radiation source to measure the dose; judge the dose distribution result: if it meets the homogenization requirements, go to S7, otherwise go to S6.

[0052] As a preferred embodiment, in S5, the method of manufacturing the equalizer includes but is not limited to precision machining or 3D printing.

[0053] Exemplarily, in this embodiment, a 3D printing process is used to manufacture a homogenizer according to the homogenizer design parameters that meet the homogenization requirements in S3, the manufactured homogenizer is loaded on a medical accelerator actually used, and the dose is measured using the equivalent water phantom method.

[0054] For example, in this embodiment, the dose distribution diagram at 10 cm below the surface of the equivalent water phantom when the homogenizer after the simulated iterative optimization is loaded is measured in S5, such as Figure 5 As shown, it can be seen that there is a certain flat area near the central axis of the field, and the symmetry is good, but the relative dose fluctuation at the edge exceeds ±5%, which fails to meet the threshold (±3% standard specified by the International Electronics Commission IEC), and the design is unqualified, and then enters S6;

[0055] S6. Measure and iterate the optimization design parameters: after making adjustments based on the current equalizer design parameters, return to S3.

[0056] For example, based on the current homogenizer design parameters, adjustments are made. The adjustments here should be made in combination with the measurement results. After the adjustments, the Monte Carlo simulation is performed again in S3. Then, the above design process is repeated. The dose distribution diagram result at 10 cm below the surface of the equivalent water phantom is obtained when the homogenizer is loaded with measurement iteration optimization, such as Figure 6 As shown, the balancing requirement is met;

[0057] S7. Complete the design of the equalizer: obtain a equalizer that meets the equalization requirements of the corresponding radiation source.

[0058] Exemplarily, in this embodiment, Figures 3 to 6 As shown, the equalizer iteratively designed using the method of the present invention has a good equalization effect on the medical accelerator, and only two iterations are required to ensure that the dose distribution is uniform and meets relevant technical standards.

[0059] The present invention designs a uniformizer for a radiation source based on Monte Carlo simulation, improves the efficiency of uniformizer design and reduces trial and error costs through simulation iterative optimization, avoids the situation where the simulation result is inconsistent with the uniforming effect in actual use through measurement iterative optimization, and the entire design process is carried out through two iterative optimization methods (simulation iterative optimization + measurement iterative optimization) to make up for each other's shortcomings, and guides the design parameters of the uniformizer structure according to the isodose line diagram, so that the uniformizer structure is no longer limited to the traditional cone or multi-stage cone shape, improves the adaptability of the uniformizer to different radiation sources, is very practical and economical, and is worthy of promotion.

[0060] The above description is only an embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the application scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for designing a radiation source homogenizer based on Monte Carlo simulation, characterized in that: The steps include: S1. Establishing Monte Carlo simulation model: establishing digital models of corresponding radiation source, homogenizer and water phantom based on Monte Carlo simulation; S2. Setting digital model input parameters: input parameters according to actual needs and initialize the digital models of the radiation source, homogenizer and water phantom; S3, perform Monte Carlo simulation: perform Monte Carlo simulation based on the established digital model, obtain the dose distribution at a plane position at a certain depth below the surface of the water phantom, and judge the dose distribution result. If it meets the uniformity requirement, proceed to S5, otherwise proceed to S4; S4, simulation iterative optimization of design parameters: adjusting the uniformizer design parameters based on the simulated dose distribution, and then returning to S3; The method for adjusting the design parameters of the equalizer is as follows: draw an isodose line map according to the dose distribution, project the isodose line map onto the surface of the equalizer, partition the surface of the equalizer according to the isodose line map, set the thickness of each partition area according to the dose level, and the thickness of the high-dose area is greater than the thickness of the low-dose area; S5. Make a homogenizer, measure and judge the dose: make a homogenizer according to the homogenizer design parameters that meet the homogenization requirements in S3, and load it on the corresponding radiation source to measure the dose; Determine the dose distribution result: if it meets the uniformity requirement, go to S7, otherwise go to S6; S6, measuring and iterating the optimization design parameters: after adjusting based on the current equalizer design parameters, return to S3; S7. Complete the design of the equalizer: obtain a equalizer that meets the equalization requirements of the corresponding radiation source.

2. The design method according to claim 1, characterized in that: In S1, the radiation source includes any one of a medical accelerator, an X-ray tube or an isotope radiation source.

3. The design method according to claim 2, characterized in that: In S1, a medical accelerator is used as a radiation source to construct a digital model of the radiation source; The digital model of the radiation source includes, from top to bottom, an electron beam, a target, a primary collimator, a homogenizer, an ionization chamber, a mirror, a secondary collimator and a water phantom.

4. The design method according to claim 1, characterized in that: In S2, the digital model input parameters include at least: radiation source parameters, uniformizer geometric parameters and materials, and the distance between the water phantom and the radiation source.

5. The design method according to claim 1, characterized in that: In S3, when the Monte Carlo simulation is performed for the first time, the leveler is initially set to a flat plate structure.

6. The design method according to claim 1, characterized in that: In S4, the method for setting the thickness of adjacent dose partitions on the leveler adopts an ellipsoid fitting method.

7. The design method according to claim 1, characterized in that: In S5, the method for manufacturing the leveler includes precision machining or 3D printing.

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