X(γ)射线全身照射过程中患者全身剂量分布的蒙特卡罗模拟

Monte Carlo simulation of whole body dose distribution in patients with total body X(γ)ray irradiation

目的对比实际测量结果探究利用蒙特卡罗方法模拟患者在实际X(γ)射线全身照射过程中全身剂量分布的可行性。方法利用MCNPX构建准确的医科达Synergy加速器6MV治疗头蒙卡模型,根据CT值与物质密度的关系将ATOM物理体模的CT转换为用于MCNPX计算的体素模型,模拟患者在X(γ)射线全身照射过程中常用的水平照射方式中全身的剂量分布,并将模拟结果与热释光剂量计在ATOM物理体模内不同位置处的测量值进行对比分析其差异。结果标准源皮距下6MV加速器治疗头模型在水模体中计算的百分深度剂量曲线和离轴剂量曲线与医院的实际测量值差异性均<2%,其中10cm×10cm射野下的最大剂量点深度约为1.5cm,与实际测量值相符。全身照射中体模内不同位置处剂量的模拟结果与热释光剂量计测量值的最大差异性约为4%,MCNPX的模拟结果与热释光的测量结果基本符合。结论MCNPX较精确地模拟计算患者全身照射的剂量分布,蒙特卡罗模拟为全身照射过程中患者全身剂量的均匀性优化提供了可能。

Objective To explore the feasibility of application of the Monte Carlo method to simulate the whole body dose distribution in patients with total body X (γ) ray irradiation by comparing the actual measurement results. Methods A Monte Carlo model of a 6 MV Elekta Synergy Clinical linear accelerator was established by MCNPX. According to the relationship between the CT value and the density of the material, the CT of the ATOM physical phantom was converted into a voxel phantom for MCNPX calculation. The dose distribution of the whole body was simulated in the total body X (γ) ray irradiation. The simulated results were compared with the measurement values of the thermoluminescence dosimetry at different positions in the ATOM physical phantom to analyze the differences. Results The difference between the depth dose curve and the off-axis dose curve and the actual measurement values calculated by the 6 MV accelerator treatment head model in the water tank was less than 2%,with the maximum dose depth of approximately 1.5 cm and field size of 10 cm×10 cm, which were consistent with the actual measurement values. The maximum difference between the simulated results at different locations in the body and the thermoluminescence dosimeter was approximately 4%, and the simulated results of MCNPX were almost in good agreement with the results of thermoluminescence. Conclusions The whole body dose distribution in patient with total body X (γ) ray irradiation can be accurately simulated by MCNPX. Monte Carlo simulation makes it possible to optimize the uniformity of the total body dose during the total body irradiation process.