金属植入物对放射治疗剂量影响的研究

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网络传输系统传人放射治疗计划系统（treatment planning system，TPS）中进行模拟计算。按照相同条件，分别用6MV和15MVX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。

Radiation dose distribution of implanted metal stent

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 - sire with 5ram 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.