目的:计算分析近距离放疗中不同粒子源、不同插植部位的剂量分布.方法:利用蒙特卡罗粒子输运工具包Geant4,计算近距离放疗中192Ir、125I两种粒子源在不同介质中剂量分布的差异,并根据美国医学物理学会43号工作组报告推荐的近距离放疗剂量计算公式(AAPM TG-43)对其重要参数进行修正.结果:计算得到192Ir源、125I源在三种不同组织等效材料中的径向剂量函数、各项异性函数.结论:(1)径向剂量函数决定于介质对光子的线能量衰减系数.衰减系数越大,径向剂量函数下降越快,反之越平缓；125I粒子源的径向剂量函数随距源距离增大而衰减的趋势远大于192Ir粒子源.(2)随着距源距离增大,骨、水等效组织中各向异性函数曲线趋于平坦,肺等效组织则没有变化.%Objective: The dose distribution is one of the most essential questions in brachytherapy. The dose varies largely between different seed and different phantom materials so accurate simulation is needed. Methods: In this paper, a Monte Carlo simulation program toolkits-Geant4 has been used to calculate the dose distribution in different phantom materials around two kinds of brachytherapy source: 192Ir and 125I, respectively. Results: The radial dose function and anisotropy function has been calculated and analyzed detailedly based on the formula recommended by the American Association of Physics in Medicine Report of the Working Group 43(AAPM TG-43). Conclusions: (1) The radial dose function depends on p, en of photon in materials and the radial dose function of I25I fall down much more sharply than 192Ir. (2) The curves of the anisotropy function in water and bone phantom materials become more plain than in lung phantom while the radial distance increases. This phenomenon reflects a law that more attenuation and scatter in materials, the curve of anisotropy function is more plain.
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