A Monte Carlo simulation method and system for iodine-131 drug therapy for thyroid tumors

Abstract

This invention discloses a Monte Carlo simulation method and system for iodine-131 drug treatment of thyroid tumors. The method includes: constructing a three-dimensional geometric model simulating radiation transport in a Monte Carlo simulation platform, including a first region model simulating neck soft tissue, a second region model embedded within this model simulating lesions, and a third region model assessing the impact of the radiation environment; configuring the physical processes simulating iodine-131 decay and particle-matter interactions based on the geometric model; defining a particle emission source based on iodine-131 decay data within the second region model; executing the simulation to obtain first energy deposition data for assessing tumor absorbed dose and second energy deposition data for assessing radiation leakage. Compared with existing technologies, this invention constructs a simulation method integrating neck, lesion, and environmental assessments, simultaneously outputting quantitative data on tumor dose and environmental leakage, achieving an intuitive quantitative assessment of the internal distribution and external impacts of the radiation field during iodine-131 treatment.

Description

Technical Field

[0001] This invention relates to the field of medical physics technology, and in particular to a Monte Carlo simulation method and system for iodine-131 drug treatment of thyroid tumors. Background Technology

[0002] Iodine-131 ( 131 I) Radiopharmaceutical therapy is the core of adjuvant therapy after surgery for differentiated thyroid cancer. Its therapeutic principle is to utilize the sodium-iodine cotransporter (NIS) of thyroid cells and cancer cells for active uptake. 131 I. Through the β-rays released during its decay, it produces a localized ionizing radiation biological effect, thereby clearing residual thyroid tissue and metastatic lesions. However, in the clinical treatment process, medical staff find it difficult to precisely control... 131 The specific trajectory and energy distribution of the rays produced by I decay within the patient's body, and... 131 In addition to releasing beta rays, I-rays also release gamma rays during decay. These rays can penetrate tissues and cause radiation to surrounding organs and the public environment. Currently, medical staff lack intuitive, visual data and quantitative assessment of the penetration and scattering of rays within the body and in space when providing services to patients and implementing radiation protection. This leads to protection plans often relying on experience-based judgment, which carries a certain degree of blindness and risk of overprotection.

[0003] A search revealed Chinese patent publication number CN106902478A, which discloses a systematic method for evaluating the biological effects of radiotherapy. This method combines Monte Carlo macroscopic simulation with voxel-level simulation, and incorporates cell damage estimation and repair process simulation to achieve an evaluation of the biological effects of radiotherapy from macroscopic dose distribution to microscopic cell lethality prediction, aiming to provide decision-making reference for personalized precision radiotherapy. However, this method is not customized for the specific scenario of iodine-131 treatment of thyroid tumors, nor does it construct a dedicated geometric model adapted to neck anatomy and lesion characteristics, or quantitatively assess environmental radiation leakage. Focusing only on cellular-level biological effects, it cannot meet the clinical needs for precise assessment of treatment dose and scientific formulation of radiation protection.

[0004] Therefore, how to intuitively and quantitatively reflect the trajectory of radiation particles in the patient's body, energy distribution, and environmental leakage during iodine-131 treatment of thyroid tumors is a technical problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the deficiencies of the prior art and provide a Monte Carlo simulation method and system for iodine-131 drug treatment of thyroid tumors.

[0006] The objective of this invention can be achieved through the following technical solutions: According to a first aspect of the present invention, a Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors is provided, the method comprising: In the Monte Carlo simulation platform, a three-dimensional geometric model is constructed to simulate radiation transport. The three-dimensional geometric model includes: a first region model for simulating neck soft tissue, a second region model embedded in the first region model for simulating lesions, and a third region model for assessing the impact of radiation environment. Based on the aforementioned three-dimensional geometric model, the Monte Carlo simulation platform is configured to simulate the radioactive decay of iodine-131 and the related physical processes of the interaction between the generated particles and matter. Within the second region model, a particle emission source based on iodine-131 decay data is defined; Based on the relevant physical processes and the particle emission source, a Monte Carlo simulation is performed to obtain first energy deposition data for assessing the tumor absorbed dose and second energy deposition data for assessing radiation leakage.

[0007] As a preferred technical solution, the first region model is a neck soft tissue model, and its construction process specifically includes: Based on multiple pre-defined cross sections distributed along the neck axis and their contour radii, a three-dimensional geometry resembling the shape of a neck is constructed. The contour radii of the cross sections are parameterized according to human neck anatomical data.

[0008] As a preferred technical solution, the second regional model is a lymphoma-tumor complex model, and its construction process specifically includes: Construct a basic geometric model of the lymphatic region and a geometric model of the spherical metastatic lesion; By using Boolean union operations, the basic lymph node region geometric model and the spherical metastatic lesion geometric model are fused in three-dimensional space to form a single composite geometry as the lymph node-tumor complex model.

[0009] As a preferred technical solution, the third region model is an environmental radiation shielding detection model, which is a hollow shell structure that completely covers the simulation space where the first region model and the second region model are located. Its material is lead or an equivalent shielding material, which is used to intercept and record radiation particles that reach the boundary after penetrating the first and second region models.

[0010] As a preferred technical solution, the configuration of the relevant physical processes specifically includes: Electromagnetic interaction physics processes used to simulate the transport, scattering, and energy deposition of electrons and photons; The specific radioactive decay physics of iodine-131 is used to simulate its β-decay and the accompanying emission of gamma photons.

[0011] As a preferred technical solution, the particle emission source is defined as follows: Based on the decay framework of iodine-131, its decay path, β-particle energy spectrum, and the energy and intensity of the accompanying γ-photon are defined. The continuous energy spectrum distribution of the β particles was simulated using an acceptance-rejection sampling algorithm. The particle emission position is fixed at a preset coordinate point inside the second region model.

[0012] As a preferred technical solution, obtaining the first energy deposition data and the second energy deposition data specifically includes: registering and managing energy accumulators corresponding to the second region model and the third region model through a parallel statistical channel manager; and during particle stepping, classifying and accumulating the energy deposition values ​​to the corresponding energy accumulators according to the logical volume where the particle is located.

[0013] As a preferred technical solution, the method further includes: distinguishing and recording the energy deposited by β particles or γ photons respectively when performing energy deposition classification and accumulation during particle stepping.

[0014] As a preferred technical solution, the Monte Carlo simulation platform includes the Geant4 simulation toolkit.

[0015] According to a second aspect of the present invention, a radiation transport simulation system for iodine-131 treatment of thyroid tumors to implement the method is provided, the system comprising: A geometric modeling module is used to construct a three-dimensional geometric model in the Monte Carlo simulation platform; the geometric model includes: a first region model for simulating neck soft tissue, a second region model embedded in the first region model for simulating lesions, and a third region model surrounding the simulated world for assessing the impact of radiation environment; The physics and source management module is used to configure the simulation of iodine-131 radioactive decay and the related physical processes of particle-matter interaction in the Monte Carlo simulation platform, and to define particle emission sources based on iodine-131 nuclear decay data in the second region model. The simulation execution and data analysis module is used to run Monte Carlo simulations and output a quantitative analysis report containing the first energy deposition data and the second energy deposition data.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention constructs a composite three-dimensional geometric model that integrates neck tissue, tumor lesions, and environmental assessment, and configures targeted physical processes and real radiation sources. It simultaneously outputs visualized particle trajectory information and quantitative data on tumor absorbed dose and environmental leakage energy, providing a scientific basis for evaluating treatment effects and formulating radiation protection measures.

[0017] 2. The three-dimensional geometric model of this invention is constructed based on human neck anatomical data and integrates the lymph-tumor complex through Boolean operations, which conforms to the actual clinical anatomical characteristics of thyroid tumor treatment, ensuring the credibility of the geometric and physical basis of the simulation and improving the reliability of the output results.

[0018] 3. This invention introduces the radioactive decay model of iodine-131 into the physical process and uses the accept-reject sampling algorithm in the source definition to simulate the β continuous energy spectrum, ensuring the accuracy of the simulation data from the decay mechanism to the energy spectrum of the emitted particles.

[0019] 4. By establishing parallel data statistics channels, this invention can automatically and synchronously complete the dose assessment of the tumor target area and the protection assessment of environmental radiation leakage in a single simulation, forming a quantitative analysis tool that integrates treatment planning and safety assessment, thereby improving the efficiency and systematic nature of the clinical workflow. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the world and world boundary layer model constructed in this invention; Figure 3 A schematic diagram of the neck model constructed for this invention; Figure 4 A schematic diagram of the central lymphatic region and metastatic lesion model constructed in this invention; Figure 5 This is a schematic diagram of the overall radiation situation in an embodiment of the present invention; Figure 6 This is a schematic diagram of the internal radiation situation of the neck in an embodiment of the present invention; Figure 7 This is a schematic diagram of the radiation situation inside the transfer stove in an embodiment of the present invention; Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] Example 1: This invention provides a Monte Carlo simulation method for radiation transport in the treatment of thyroid tumors using iodine-131 drugs, such as... Figure 1 As shown, the method includes: Step S1: Geometric modeling and configuration, constructing a composite three-dimensional geometric model that includes a model of neck soft tissue and tumor lesions with anatomical features, as well as a detection structure for assessing the impact of radiation environment, to provide accurate spatial scene and material definition for simulation; Step S2: Physical process setup. Configure the physical processes necessary for the simulation in the simulation platform, especially by introducing a high-precision electromagnetic interaction model and a dedicated iodine-131 radioactive decay physics model to accurately describe the transport and interaction behavior of β particles and γ photons. Step S3: Radiation source definition. Inside the tumor lesion model, a particle emission source based on real nuclear decay data of iodine-131 is precisely defined, including simulating its continuous β energy spectrum, accompanying γ photons, and isotropic emission characteristics, to ensure that the source terms are consistent with the actual clinical situation. Step S4: Output data specification: Establish and configure a targeted data acquisition system to specify and record key data for quantifying the treatment effect (energy deposition in the tumor area) and radiation protection level (energy leakage at the environmental boundary), and to distinguish the contribution of different particles; Step S5: Simulation execution and control. Execute the simulation and finally obtain and output the visualization information of the motion trajectory of the radiation particles in the geometric model, as well as the quantified energy deposition data.

[0023] The following are the specific implementation details for each step: Step S101: This step uses the Geant4 platform as an example to construct the complete three-dimensional geometry required for simulation. This structure is a hierarchical composite model designed to realistically reflect the patient's neck anatomy, tumor lesion distribution, and the environment required for radiation environmental impact assessment.

[0024] Step S1011: Construct the world and world boundary layer model like Figure 2 As shown, a cube-shaped space with a side length of 4 meters is created as the simulated world. It is implemented using the G4Box geometric primitive and given the standard air material (G4_AIR) property, forming a simulation space with air as the medium. Its physical entity is positioned at the origin of the three-dimensional coordinate system (0, 0, 0). This world serves as the container for all geometric structures.

[0025] To quantify the impact of radiation on the surrounding environment during treatment, a boundary detection layer encasing the outer surface of the simulated environment was simultaneously constructed. Using Boolean subtraction, an inner cube offset inward by 3 cm was subtracted from an outer cube of the same size as the simulated environment, resulting in a hollow shell structure with a thickness of 3 cm. This shell was coated with a high-density, high-atomic-number shielding material; in this embodiment, lead (G4_Pb) was chosen, and it was positioned at the center of the simulated environment. This model, serving as a third-region model, intercepts, records, and quantifies radiation particles escaping from the human model to the boundary of the simulated environment, directly contributing to radiation protection assessment.

[0026] Step S1012: Construct a neck soft tissue model like Figure 3 As shown, a neck soft tissue model is constructed using a multi-section revolute (G4Polycone) as the first region model. This model is based on human neck anatomy data. It simulates the natural variations in neck thickness by defining five sections distributed along the neck axis (Z-axis), for example, Z-coordinates of -50mm, -20mm, 0mm, 20mm, and 50mm. The outer radius array for each section is [55.0, 50.0, 45.0, 50.0, 55.0] mm, with an inner radius of 0 mm. A logical volume is created for this geometry, and the material is specified as the water equivalent material (G4_WATER) from the NIST database to simulate the radiation interaction characteristics of soft tissues (muscle, fat, etc.). Finally, the neck model is positioned at the origin of the world coordinate system, and its parent volume is set as the world logical volume.

[0027] Step S1013: Constructing a lymphocyte-tumor complex model Within the neck model, a lympho-tumor complex model is constructed to simulate the lesion, serving as a second region model. For example... Figure 4 As shown, first, a cylindrical-like object with a gradient along the Z-axis is created using G4Polycone, with its outer radius gradually changing from 5mm to 15mm, forming a lymphatic region geometry; then, a spherical metastatic lesion geometry with a radius of 2.5mm is generated using G4Sphere to simulate a typical metastatic lesion morphology. Using G4UnionSolid Boolean union operations, the aforementioned lymphoid basic model and spherical tumor model are merged into a single composite geometry. During the merging process, the spherical tumor model is spatially offset relative to the lymphoid body to coordinates (8, 8, 8) mm to simulate the actual spatial distribution of metastatic lesions within the lymphoid region. The constructed composite structural model is as follows: Figure 4 As shown; Assign a logical volume to the merged composite and specify the material properties as ICRP (International Commission on Radiological Protection) standard soft tissue material (G4_TISSUE_SOFT_ICRP) to more accurately simulate the radiation characteristics of biological tissue; Finally, the lymphoma complex model was located inside the constructed neck model using G4PVPlacement, with specific coordinates of (0, 35, 0) mm, thus establishing a complete and anatomically significant target geometric model.

[0028] Step S201: To achieve accurate simulation of iodine-131 decay and the transport behavior of its generated particles in biological tissues, a corresponding list of physical processes needs to be configured in Geant4.

[0029] In this embodiment, G4EmStandardPhysics_option4 is selected as a high-precision electromagnetic interaction physics model to accurately simulate the ionization, excitation, and scattering behavior of electrons and photons. At the same time, G4RadioactiveDecayPhysics radioactive decay physics model is introduced, which is specifically used to simulate the β decay of iodine-131 nuclei and the accompanying emission of γ photons.

[0030] The combination of these two physical models provides a reliable physical foundation for subsequent simulations.

[0031] Step S301: This step defines the particle emission source within the constructed geometric model based on the actual nuclear decay characteristics of iodine-131.

[0032] Step S3011: Define decay data. Based on the decay profile of iodine-131, define the key parameters of its main decay paths in the program, including the maximum energy of the β particle, the branch ratio of each path, and the energy and emission intensity of the accompanying γ photon. This embodiment covers the main decay modes with a cumulative intensity of 89.9%. Step S3012: Simulate the continuous energy spectrum of β particles. The β particles released by iodine-131 have a continuous energy spectrum from zero to a maximum value. In this embodiment, the accept-rejection sampling algorithm based on Fermi theory is used to randomly generate β particle energies that conform to the distribution of this continuous energy spectrum in each simulation event, so as to accurately reproduce the actual energy spectrum shape. Step S3013: Determine the spatial location of the source and fix the particle emission vertex at a specified coordinate point inside the tumor model. In this embodiment, it is set to (8, 43, 8) mm. This position corresponds to the spatial location of the constructed spherical metastatic lesion model, ensuring the consistency between the radiation source and the geometric model of the lesion.

[0033] Step S3014: Generate particle events. At the beginning of each simulation event, the program randomly selects a specific decay path according to the predefined decay branch ratio. Subsequently, a β particle (electron) that conforms to the energy spectrum characteristics is generated, and an accompanying γ photon is generated according to the probability of the selected path. These particles are created as different primary particles in the same decay event.

[0034] Step S3015: Set the emission direction and adopt an isotropic emission mode, that is, the initial momentum directions of β particles and γ photons are randomly generated by calling the G4RandomDirection() function to simulate the randomness of the direction of radionuclide decay.

[0035] Step S401: To obtain the critical quantitative data needed to assess treatment effectiveness and radiation safety, a corresponding data recording mechanism needs to be set up in the simulation.

[0036] Step S4011: Establish a statistical channel and register and manage two parallel energy accumulators using G4AccumulableManager: Tumor region dose accumulator: used to accumulate the total energy deposition (denoted as fEdep) and its sum of squares (fEdep2, used to calculate the statistical variance) recorded in the lympho-tumor complex model. Environmental leakage dose accumulator: used to accumulate the total energy deposition (denoted as fBoundaryEdep) and its sum of squares (fBoundaryEdep2) recorded within the world boundary layer model. Step S4012: Implement stepping process recording. In the user-defined SteppingAction class, implement refined energy deposition identification and classification: Volume recognition: The logical volume of the current particle step is obtained through Geant4's geometric navigation system; Energy attribution: If the step occurs within the lympho-tumor complex or the world boundary layer, the energy value deposited in that step is added to the corresponding energy accumulator. Particle identification: Simultaneously record the particle type (electron or gamma photon) of the deposited energy to support subsequent analysis of the contribution of different radiation components; Step S4013: Complete post-run processing, and summarize the data after the simulation ends in the EndOfRunAction class: Data merging: In a multi-threaded simulation environment, the accumulator data of each worker thread is reduced and merged to obtain global statistics; Statistical analysis: Calculate statistical quantities such as total depositional energy, mean, and standard deviation; Output results: Print the formatted results, including: total absorbed energy in the tumor region, total energy leaked from the boundary layer, total number of simulated primary events, and basic information about the radiation source.

[0037] Step S501: By executing preset macro command scripts, the entire Monte Carlo simulation process can be started and controlled.

[0038] Step S5011: Initialization. Execute the / run / initialize macro command to enable the Geant4 kernel to complete initialization based on the constructed geometry and physics processes, thus building a stable simulation environment. Step S5012: Visual initialization, execute the / vis / open command to start the visualization driver, such as OpenGL; enable automatic view refresh by / vis / viewer / set / autoRefresh true, and execute the / vis / drawVolume command to draw all the established geometric models; Step S5013: Trajectory display settings, execute / vis / scene / add / trajectories smooth to add smooth particle trajectory display; establish a trajectory coloring scheme distinguished by particle type through / vis / modeling / trajectories / create / drawByParticleID; set / vis / scene / endOfEventAction accumulate to realize the cumulative display of trajectories for multiple events; Step S5014: Perform simulation and obtain results. Execute the command / run / beamOn 100 to start a Monte Carlo simulation of 100 primary events. During the simulation, particle transport, interaction and energy deposition are calculated and recorded in real time.

[0039] After the simulation, the system outputs key results: Visualization results: such as Figure 5 As shown, the overall distribution of radiation particles emitted from the tumor region in the simulated space is obtained; as Figure 6 As shown, the propagation path of radiation particles within neck tissue was obtained; as Figure 7 As shown, the fine distribution of radiation particles within the tumor was obtained; Quantitative data: After simulating 100 iodine-131 radioactive decay events in this embodiment, the total energy deposition data of iodine-131 in the central lymph node region and metastatic lesions (second region model) was obtained as 59.5001 MeV, and the total energy deposition data in the world boundary layer (third region model) was obtained as 54.7538 MeV. This fully presents the energy deposition distribution of iodine-131 decay rays at the boundary between the target lesion and the environment, providing a direct and reliable basis for quantitatively assessing the tumor absorbed dose and radiation protection effect.

[0040] The method of this invention constructs a composite geometric model that includes the anatomical structure of the neck, the tumor lesion, and the environmental shielding detection layer. It configures a high-precision physical process for iodine-131 decay, defines a real radiation source within the lesion, runs a simulation, and finally outputs a visualized image of the trajectory of radiation particles and quantitative data on the tumor absorbed dose and the energy leaked into the environment. This provides an intuitive and quantitative analysis tool for solving problems such as unclear radiation distribution and lack of basis for protection assessment in clinical practice.

[0041] Example 2: This invention provides a radiation transport simulation system for iodine-131 treatment of thyroid tumors to implement the above-described method. This system can be implemented in software, hardware, or a combination of both, for example, as a dedicated simulation software suite installed on a high-performance computing workstation or server. The system mainly includes the following functional modules: World and Boundary Building Block: Used to create a simulated world cube and the hollow shell boundary layer that surrounds it, and allows you to specify the properties of air and shielding materials (such as lead); Anatomical structure building unit: used to build a soft tissue model that conforms to the neck contour by calling the rotational geometry primitives based on the input anatomical parameters, such as cross-sectional coordinates and radius arrays; Lesion Complex Building Unit: Used to build a basic lymphoid model and a spherical metastatic lesion model, and to fuse them into a single lymphoid-tumor complex model through Boolean union operation, supporting the setting of spatial offset during fusion.

[0042] Physical and Source Management Module: This module executes steps S3 and S4 in Example 1; it includes: Physical Process Management Unit: Used to select and activate high-precision electromagnetic interaction processes and radioactive decay physical processes from the list of physical processes in the simulation platform; Radioactive source definition unit: Used to generate β particles that conform to the continuous energy spectrum and generate corresponding accompanying γ photons based on a preset iodine-131 decay database (containing information such as energy spectrum and branching ratio) using an accept-reject sampling algorithm. This unit allows users to specify the precise spatial coordinates of the particle emission (located inside the tumor model). Simulation Execution and Data Analysis Module: This module is responsible for executing steps S4 and S5 in Example 1, and includes: Simulation control unit: Used to receive simulation parameters (such as the number of events), call the platform kernel to execute Monte Carlo simulation, and manage runtime options such as visualization; Data acquisition unit: Built-in parallel statistical channel manager, used to register and manage energy accumulators corresponding to tumor regions and boundary layers respectively. During the simulation, it identifies the particle step position in real time and classifies and accumulates the energy deposition value to the correct accumulator, while also supporting the differentiation of contributions from different particle types; Report generation unit: After the simulation is completed, it automatically merges multi-threaded data, calculates statistics (such as total dose, mean, standard deviation), and generates a quantitative analysis report containing key indicators such as tumor absorbed dose and radiation leakage dose. Visualization renderer: Generates 3D visualizations of particle trajectories in real time or offline during or after the simulation.

[0043] Through the collaborative work of the aforementioned modules, this system provides users with a dedicated simulation tool for iodine-131 thyroid tumor treatment planning and radiation safety assessment. By configuring the corresponding anatomical parameters and simulation options, users can automatically obtain intuitive and visualized radiation distribution maps and quantitative dose assessment data, enabling medical staff to intuitively see the radiation trajectory and quantitative assessment data, thereby assisting in treatment decisions and radiation protection design.

[0044] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A Monte Carlo simulation method for iodine-131 drug therapy of thyroid tumors, characterized in that, include: In the Monte Carlo simulation platform, a three-dimensional geometric model is constructed to simulate radiation transport. The three-dimensional geometric model includes: a first region model for simulating neck soft tissue, a second region model embedded in the first region model for simulating lesions, and a third region model for assessing the impact of radiation environment. Based on the aforementioned three-dimensional geometric model, the Monte Carlo simulation platform is configured to simulate the radioactive decay of iodine-131 and the related physical processes of the interaction between the generated particles and matter. Within the second region model, a particle emission source based on iodine-131 decay data is defined; Based on the relevant physical processes and the particle emission source, a Monte Carlo simulation is performed to obtain first energy deposition data for assessing the tumor absorbed dose and second energy deposition data for assessing radiation leakage.

2. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 1, characterized in that, The first region model is a neck soft tissue model, and its construction process specifically includes: Based on multiple pre-defined cross sections distributed along the neck axis and their contour radii, a three-dimensional geometry resembling the shape of a neck is constructed. The contour radii of the cross sections are parameterized according to human neck anatomical data.

3. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 1, characterized in that, The second regional model is a lymphoma-tumor complex model, and its construction process specifically includes: Construct a basic geometric model of the lymphatic region and a geometric model of the spherical metastatic lesion; By using Boolean union operations, the basic lymph node region geometric model and the spherical metastatic lesion geometric model are fused in three-dimensional space to form a single composite geometry as the lymph node-tumor complex model.

4. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 1, characterized in that, The third region model is an environmental radiation shielding detection model, which is a hollow shell structure that completely covers the simulation space where the first region model and the second region model are located. Its material is lead or equivalent shielding material, and it is used to intercept and record radiation particles that reach the boundary after penetrating the first and second region models.

5. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 1, characterized in that, Configuring the relevant physical processes specifically includes: Electromagnetic interaction physics processes used to simulate the transport, scattering, and energy deposition of electrons and photons; The specific radioactive decay physics of iodine-131 is used to simulate its β-decay and the accompanying emission of gamma photons.

6. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 1, characterized in that, The particle emission source is defined as follows: Based on the decay framework of iodine-131, its decay path, β-particle energy spectrum, and the energy and intensity of the accompanying γ-photon are defined. The continuous energy spectrum distribution of the β particles was simulated using an acceptance-rejection sampling algorithm. The particle emission position is fixed at a preset coordinate point inside the second region model.

7. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 1, characterized in that, Acquiring the first and second energy deposition data specifically includes: registering and managing energy accumulators corresponding to the second and third region models through a parallel statistical channel manager; and during particle stepping, classifying and accumulating the energy deposition values ​​to the corresponding energy accumulators according to the logical volume where the particle is located.

8. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 7, characterized in that, The method further includes: distinguishing and recording the energy deposited by β particles or γ photons separately when performing energy deposition classification and accumulation during particle stepping.

9. The Monte Carlo simulation method for iodine-131 drug treatment of thyroid tumors according to claim 1, characterized in that, The Monte Carlo simulation platform includes the Geant4 simulation toolkit.

10. A radiation transport simulation system for iodine-131 treatment of thyroid tumors to implement the method as described in any one of claims 1-9, characterized in that, include: A geometric modeling module is used to construct a three-dimensional geometric model in the Monte Carlo simulation platform; the geometric model includes: a first region model for simulating neck soft tissue, a second region model embedded in the first region model for simulating lesions, and a third region model surrounding the simulated world for assessing the impact of radiation environment; The physics and source management module is used to configure the simulation of iodine-131 radioactive decay and the related physical processes of particle-matter interaction in the Monte Carlo simulation platform, and to define particle emission sources based on iodine-131 nuclear decay data in the second region model. The simulation execution and data analysis module is used to run Monte Carlo simulations and output a quantitative analysis report containing the first energy deposition data and the second energy deposition data.

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