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 MVX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-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.