Monte Carlo Simulation on the Irradiation Damage of Contaminative Electrons to the Skin Cell in External Radiotherapy

Key words: 
• contaminative electron /
• skin cell /
• Monte Carlo simulation /
• damage yield

Abstract: The cell damage yield was simulated to investigate the micro-damage mechanism of the contaminative 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 DSB. 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 tissue. The lethal coefficient " 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 assuming α=0.3 Gy^-1 and α/β =10 Gy, the " increment is less than 1% when the incident electron increases up to 103. However, the ε increment will increase 3% s 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.