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采用Geant4-DNA低能物理模型研究了污染电子在细胞DNA水平上的物理作用和能量沉积。利用密度聚类算法分析了损伤产额分布；并结合皮肤细胞辐射敏感性参数和临床表征剂量，探讨了低能电子对皮肤细胞的损伤特征。模拟发现，产生的DSB中约20%是cDSB；DSB产额是SSB的约4%；损伤聚类包含的SSB一般63个，20 keV和100 keV电子也可造成>5个SSB的聚类损伤；晚反应、高α值的组织更应注意防护低能电子辐射；由于LQ模型中剂量平方项的影响，cDSB损伤致死系数ε随入射电子数目的增加而增大。当105个电子入射时，ε的数值可较单个电子增大3%～15%。可通过调节直接电离损伤概率弥补间接损伤产额，研究细胞辐照损伤的内在机理。本工作建立的低能电子对细胞DNA的损伤模型及结果，可用于评价放疗中低能污染电子对皮肤细胞的损伤效应。

The cell damage yield was simulated to investigate the micro-damage mechanism of the contam-inative electron to the skin cell in external radiotherapy. The physical interaction and the energy deposited events of contaminative electrons in the cell DNA were modeled based on Geant4-DNA low energy physical model. The density-based cluster mining algorithm was used to analyze the micro-damage yield and obtain its detailed compositive information. By taking the irradiation sensitive parameter and the clinical feature dose threshold of the skin cell into consideration, the damage features of the low energy contaminative electron to the skin cell were studied. The DSB and SSB yield and ratio, the cluster size and the root mean square radius, the cell SF and the lethal coefficient ε of the complex cDSB were researched. The results show that there is about 20% cDSB in the DSB yield, the other is iDSB. And the yield of DSB is about 4% of that of the SSB. Generally the cluster size includes less than 3 SSBs, in which 1 or 2 SSBs cluster size is more than 99% and>3 SSBs cluster size is less than 1%. However, for some very low energy electrons such as 20 keV and 100 keV, the cluster size can be more than 5 SSBs. The irradiation protection will be more crucial for the later response and the high α tissue. The lethal coefficient ε of the complex cDSB will increase with the incident electron number and the accumulative dose increasing for the dose square term in LQ model. If assumingα=0.3 Gy-1 andα/β=10 Gy, theεincrement is less than 1%when the incident electron increases up to 103. However, theε increment will increase 3%～15% (e.g. 13.8% for 30 keV and 3.4% for 200 keV electrons) when the incident electron increases up to 105. The simulation of the direct physical damage of the cell can be adjusted by a probability parameter to offset the simulation of the indirect biochemical damage. Thus the micro-damage mechanism of the contaminative electron to the skin cell can be detected at a certain extent by Monte Carlo physical simulation. This damage model of the low energy electron to DNA and these simulated results could be used to evaluate the damage effect of the low energy contaminative electron to the skin cells in the external radiotherapy.