Objective : To determine the scattering effect of implanted metal stent on radiation dose distribution and define the mathematical correction parameters for post - implantation irradiation dose calculation.Methods: The phantom with nickel - titanium alloy stent was scanned by CT - sim with 5mm slice.The CT images were transferred to TPS ( treatment planning system) by LANTIS network, and the interest point dose was calculated.According to the scan condition, the radiation was done with 6 MV and 15 MV X - ray.The dose was measured by TLD and FAMAR irradiation chamber.The result calculated from the TPS was compared with the measurement datum.Results: The measurements showed an increase in absorbed dose of up to 3.9％ in 6 MV and 6.6％ in 15 MV x - rays before the surface of stent, up to 2.8％ in 6 MV and 6.3％ in 15 MV x - rays after the surface of stent.The errors become smaller with the distance increase.Conclusion : The presence of stent increased the dose, which could lead to radiation damage , so the radiation dose should be amended while making radiotherapy planning.%目的:测量金属内固定支架对放射治疗剂量的影响,对采用金属内固定的肿瘤患者放射治疗提供剂量修正的临床数据.方法: 按照测量条件,将带有金属内固定支架的体模在螺旋CT下进行扫描,层厚为5mm,图像通过LANTIS网络传输系统传入放射治疗计划系统(treatment planning system,TPS)中进行模拟计算.按照相同条件,分别用6MV和15 MV X线照射,用热释光剂量仪和FAMER型电离室对钛镍合金支架界面以及界面上下一定深度分别测量,并与放射治疗计划系统计算结果比较.结果: 实际测量与TPS计算存在一定误差,实测值明显大于TPS计算值,支架前表面的误差最大可达3.9% (6MV)和6.6%(15MV),支架后表面的误差最大为2.8%(6MV)和6.3%(15MV),距表面距离越远,误差越小.结论: 镍钛合金支架患者放射治疗时,实际测量剂量比TPS计算剂量要大,有可能增加放射性损伤.TPS计算过程中,虽然对金属物进行了密度修正,但仍存在一定误差,有必要在制订放疗计划时对照射剂量进行修正.
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