用蒙特卡罗方法模拟实验体内金属植入物对放疗剂量分布影响

Impact of implanted metal plates on radiation dose distribution in vivo by Monte Carlo code

目的用蒙特卡罗（MC）模拟实验体内植人金属物后的百分深度剂量变化。方法用6MVX线照射水下5cm处0．4cm厚金属植入物，对有无金属植入物百分深度剂量变化进行MC方法模拟实验并比较结果。结果6MVX线照射置入不锈钢板、钛合金板比不用植入物时入射面剂量分别增加19．6％、15．7％，不锈钢板、钛合金板入射面0．3cm以外影响〈1．5％。不锈钢板、钛合金板出射面剂量分别减少8．6％、8．2％，剂量影响〈1．5％时距离出射面1．2、0．9cm。不锈钢板比钛合金板入射面剂量大3．9％，出射面剂量相似。结论MC方法是一种能快捷、准确的计算方式，金属植入物对放疗剂量影响明显，相同条件下不锈钢对入射面剂量影响大于钛合金钢板。

Objective To investigate the impact of metal plate on radiation dose distribution by Monte Carlo （MC） code. Methods The metal plates with 0. 4 thick were placed in water at 5 cm, all the plate irradiated with 6 MV X-ray were simulated by MC code, SSD = 100 cm. The percentage depth dose with or without metal implants were compared. Results The surface absorbed doses on incident plane of stainless steel plate and titanium plate were increased by 19. 6% and 15.7% respectively as compared water, the dose influence was less than 1.5% more than 0. 3 cm outside the incidence plane. The doses on the exit surface of stainless steel plate and titanium plate were lowered by 8.6% and 8.2% when compared with water, the dose impacts of this places where were from the exit surface of stainless steel plate,titanium plate more than 1.2 cm,0. 9 cm were less than 1.5%. The surface absorbed doses on incident plane of stainless steel plate were increased by 3.9% respectively as titanium plate, the dose of the exit surface of stainless steel plate and titanium plate was similar. Conclusions MC method is a fast and accurate calculation method. The influence of metal plate on the radiotherapy dose distribution is significant. Under the such condition, the impact of stainless steel plate is much more than that of titanium alloy plate.