容积调强放射治疗多叶准直器质量保证方法

Quality assurance of multileaf collimator in volumetric modulated arc therapy

目的:研究容积调强放射治疗模式下多叶准直器质量保证的方法。方法:检测容积调强多叶准直器(Multileaf Collimator,MLC)叶片运动到位精度,分析Rapid Arc在不同条件下MLC误差变化。选取6例直肠癌容积调强病人,自编软件采集MLC治疗日志文件,读取实际治疗时每条弧各个控制点的MLC各个叶片的位置,代替计划文件中的叶片位置信息,重新导入治疗计划系统并进行三维剂量重建。与治疗计划比较,分析叶片位置误差及其导致的剂量学差别。结果:MLC的到位精确度分析显示,各分次的MLC图像极度吻合,匹配良好;6例容积调强病人叶片位置误差均<2 mm,大部分误差集中在0.05 mm^1 mm范围内。MLC叶片位置误差对计划靶区V45的影响较大,差异有统计学意义;叶片误差对小肠、膀胱、股骨头等危及器官的影响较小,差异无统计学意义。结论:MLC叶片位置精度影响到治疗计划剂量的精度,需要进行严格的质量保证。

Objective To explore the quality assurance method of multileaf collimator （MLC） in volumetric modulated arc therapy （VMAT）. Methods The MLC leaf position accuracy in VMAT was examined. With different conditions of RapidArc MLC, the leaf position errors were analyzed. Six rectum patients receiving VMAT were randomly selected. During the actual treatment, MLC leaf positions at every control point on each arc were recorded in MLC dynamic log files by self-programmed software. And the recorded leaf position replaced leaf positions in planning files, re-importing new information into the treatment planning system to reconstruct three dimensional （3D） dose distribution. Compared with treatment plan, MLC leaf position errors and dose differences were analyzed. Results MLC position accuracy analysis showed that MLC images of each fraction were extremely consistent and well-matched. All the MLC leaf position errors of these six patients were less than 2 ram, and most of errors was between 0.05 mm and 1 ram. MLC leaf position errors had a great influence on planning target volume （V：0o）, with statistically significant differences, while the leaf position errors had a small impact on small intestine, bladder, femoral head, without statistically significant differences. Conclusion Quality assurance should be strictly implemented because the MLC leaf position accuracy can affect the accuracy of treatment planning dose.