容积旋转调强多叶准直器叶片位置误差分析研究

Analysis of multi-leaf collimator leaf position deviation in volumetric modulated arc therapy

目的 研究鼻咽癌容积旋转调强计划执行过程中多叶准直器叶片的位置误差，验证一种检测叶片到位精度的方法。方法 随机数字表法选取32例鼻咽癌患者的容积旋转调强双弧计划，分别为第1个治疗弧（顺时针181°-179°）与第2个治疗弧（逆时针179°-181°），每个治疗弧包含A、B两组叶片，使用Argus软件提取在Varian Trilogy加速器上计划实际执行时的Dynalog文件，比较叶片实际位置与计划位置间的差别。结果 所有计划在±2、±1.5、±1和±0.5 mm位置误差以内的叶片占比分别为99.99%、99.90%、99.07%和93.98%；第1、2个治疗弧和A、B组在±1 mm位置误差以内的叶片占比分别为98.08%、100%和98.97%、99.01%。第1个治疗弧与第2个治疗弧的叶片位置误差范围分别为-2.95~2.99和-0.22~0.23 mm，差异有统计学意义（t=2.35，P〈0.01）；A与B组的叶片位置误差范围分别为-2.95~2.68和-2.92~2.99 mm，差异无统计学意义（P〉0.05）。结论 容积旋转调强计划执行中，叶片到位精度在误差控制范围内，多个治疗弧计划验证时需要考虑对治疗弧分别验证，日志文件分析可作为加速器叶片到位精度检测的一种行之有效的方式。

Objective To evaluate the position deviation of multi-leaf collimator （MLC） in volumetric modulated arc therapy for nasopharyngeal carcinoma and to verify a method of detecting the leaf position accuracy. Methods Thirty-two volumetric modulated arc plans of nasopharyngeal carcinoma were randomly selected. A clockwise arc with a gantry range of 181° to 179° and a counterclockwise arc with a gantry range of 179° to 181° were used for each plan. Each arc contained two leaf groups, groups A and B. By using the Argus software, the actual MLC leaf positions were extracted from the Dynalog files in the Varian Trilogy accelerator. The planed MLC leaf positions were compared with the actual positions, and the differences were calculated between them. Results The proportions of the leaf position errors within ±2, ±1.5, ±1 and ±0.5 mm were 99.99%, 99.90%, 99.07% and 93.98%, respectively. The proportions of the leaf position errors within ±1 mm were 98.08%, 100%, 98.97% and 99.01% for the first therapeutic arc （ARC1）, second therapeutic arc （ARC2）, A and B groups, respectively. The leaf position errors range of ARC1 and ARC2 were -2.95 to 2.99 and -0.22 to 0.23 mm （t=2.35, P〈0.01）. The leaf position errors range of leaf bank A and leaf bank B were -2.95 to 2.68 and -2.92 to 2.99 mm （P〉0.05）. Conclusions During the volumetric modulated arc radiotherapy, the leaf positions deviation are in control. The Dynalog files can be used as an effective way to analysis the leaf position errors.