体内金属植入物对放疗剂量分布影响

摘要

目的 探讨放射野内金属植入物对其周围组织吸收剂量的影响.方法 将骨科内固定不锈钢板、钛合金板和相同大小条状肌肉分别置入尸体标本左侧股骨前侧,构建实验组与对照组模型.应用直线加速器6 MV X线照射,使用热释光剂量仪分别对不同内植物界面的吸收剂量进行测量,用治疗计划系统对有无金属植入物百分深度剂量变化进行模拟计算并与测量结果 比较.结果 6MVX线照射置入不锈钢板、钛合金板和条状肌肉时,入射面实际测量值分别为1.18 Gy±0.04 Gy、1.12 Gy±0.04 Gy和0.97 Gy±0.03 Gy(F=57.35,P<0.01),不锈钢板和钛合金板较条状肌肉相应位置吸收剂量分别增加了21.65%和15.46%;出射面实际测量值分别为0.87 Gy±0.03 Gy、0.90Gy±0.02 Gy和0.95 Gy±0.04 Gy(F=13.37,P<0.01),不锈钢板和钛合金板较条状肌肉相应位置点吸收剂量分别衰减了8.42%和5.26%.模拟计算钢板入射面1 cm范围内吸收剂量较条状肌肉明显增加,而钢板入射面1 cm以外范围影响<5%,出射面对剂量分布影响<2%.结论 金属植入物对放疗剂量分布存在明显影响,吸收剂量可产生5%～22%偏差;相同条件下不锈钢板对射线剂量分布影响较钛合金板明显.%Objective To investigate the impact of metal plate on radiation dose distribution in surrounding tissues in cadaver specimens.Methods Stainless steel plate, titanium plate, and muscle strip were implanted into the left thigh of a corpse, respectively.All the specimens were irradiated with 6 MV X-ray , SSD = 100 cm.The absorbed dose of surface was measured by thermoluminiscent elements.Results Surface dose distributions differed significantly among the three different materials (F = 57.35, P < 0.01),with the amounts of 1.18 Gy ± 0.04 Gy (stainless steel plate), 1.12 Gy ± 0.04 Gy (titanium plate) and 0.97 Gy ±0.03 Gy (muscle strip), respectively.The surface absorbed doses on incident plane of stainless steel plate and titanium plate were significantly increased by 21.65% and 15.46% respectively as compared with that of muscle strip.The absorbed doses on the exit surface of stainless steel plate, titanium plate and muscle strip were 0.87 Gy ± 0.03 Gy, 0.90 Gy ± 0.02 Gy and 0.95 Gy ± 0.04 Gy, respectively (F =13.37, P <0.01).The doses on the exit surface of stainless steel plate and titanium plate were significantly lowered by 8.42% and 5.26% when compared with that of muscle strip.Using treatment planning system,the differences between dose distribution with and without metal plate were compared.Within 1 cm away from the incident plate, there was an obvious increase in the absorbed dose, while the influence was less than 5% 1cm outside the surface.The effect of dose distribution on exit surface was less than 2%.Conclusions The influence of metal plate on the radiotherapy dose distribution is significant.The deviations ranges from 5% to 29%.Under the same condition, the impact of stainless steel plate is much more than that of titanium alloy plate.