采用蒙特卡罗(MC)技术研究放射性核素131I的放疗特性。给出了131I衰变过程的MC抽样表达式，实现了含电子和光子的混合抽样模拟。对水客体中131I衰变的MC模拟结果表明：131I能够有效地治疗甲状腺肿瘤而几乎不影响正常组织。变密度客体的MC模拟结果表明：沉积能量与面密度之间的关系与密度无关，满足卷积核自适应的要求；并且MC模拟能够提供剂量卷积核函数，为快速剂量计算提供数据。

The convolution core is the key factor to calculate dose with the convolution method in single-photon emission computed tomography (SPECT) diagnosis. The Monte Carlo (MC) technology was used to investigate the dose characteristic of the SPECT diagnosis with the radioactive isotope 131I. The expression of the 131I decay was given and was used to achieve the simulation of the electron and the photon of one decay of the 131I. The SPECT object is a spherical water phantom. The MC simulation results not only show that 131I can cure the hypothyroid caner and almost has no harm to the normal tissue, but also verify that the requirement of the self-adaption convolution core is met, for the relationship between the deposited energy and the areal mass is nothing to the density. The convolution core is gained by the MC simulation and is very useful to fast dose calculation.