放疗污染电子来源及去除方法的Monte Carlo模拟研究

The Monte Carlo simulation study on origin and removal methods of contamination electrons in radiotherapy

利用Monte Carlo程序模拟研究了放射治疗过程中污染电子的产生规律及剂量学特性,并进一步研究充氦及安置铅过滤板两种方法减少污染电子的效果。结果表明:污染电子主要来源于加速器机头和空气的散射,并随射野面积和初级光子束能量的增加而增加;充氦能够有效地减少初级光子束与空气反应产生的污染电子;安置铅过滤板能够有效减少机头部件散射的污染电子;同时使用两种方法后,来源于机头部件与空气的污染电子均有较大程度减少。因此,使用充氦和铅过滤板可以有效减少污染电子造成的皮肤表面剂量,达到较好保护皮肤组织的目的。

Monte Carlo simulation was used to study the dosimetric characteristics and the yield of contamination electrons, as well as eletron removal efficiency of applying helium and lead-filter. The results showed that most contamination electrons came from accelerator head components and air, and the amount increased with the increment of beam field size and primary photon energy. Instead of air, Helium loading in the accelerator head could significantly reduce the electrons scattering from air, and lead-filter could block the electrons caused by accelerator head components effectively. When both methods were used simutaneously, the majority of electrons could be eliminated. Therefore, employing Helium and lead-filter at the same time is an effective way to reduce the dose delivered on the surface and protect the skin tissue.