摘要目的 设计一种检测静态调强计划实施过程中多叶准直器(MLC)叶片到位精度的方法,并分析叶片误差对靶区和正常器官受量的影响.方法 选取20例已通过剂量验证的静态肺癌调强计划,按子野数目从小到大排序,将前10例和后10例计划分别编入简单计划组和复杂计划组,将计划传送给瓦里安600CD加速器执行,借助PV aS500电子射野影像装置(EPID)拍摄图像,通过梯度算法获取叶片的实际位置,计算出叶片验证通过率,并根据检查的结果修改MLC文件,在其他参数不变的情况下重算计划,得到叶片误差存在前后靶区和正常器官受量的变化情况.结果 20例病例中大多数器官的受量均有增加或减少,且第6例和第13例病例中的脊髓Dmax超过了45 Gy的限值.简单计划组中只有脊髓Dmax的变化差异具有统计学意义(t=-3.08,P＜0.05),复杂计划组的PGTV D95％、PTV D95％、脊髓Dmax、肺V20、心脏V40的变化差异都具有统计学意义(t=-1.89、-1.99、-2.36、-2.55、-1.85,P＜0.05).结论 为了确保治疗的安全和疗效,需要对叶片走位进行检测,特别是对子野数目较多的复杂计划,使用电子射野影像装置和计划系统能够检测出计划执行过程中叶片的到位情况,以及靶区和正常器官的实际受量.

abstractsObjective To design a method for detecting multileaf collimator (MLC) leaf position accuracy in implementing a static intensity-modulated plan and to analyze the impacts of leaf errors on dose of targets and normal organs.Methods Static intensity-modulated planning for twenty lung cancer cases through dose verification was sorted in an ascending order according to the number of segment,and then the first and the last 10 plans were sorted as the simple plan group and the complex plan group,respectively.These plans were transmitted to a Varian 600CD accelerator and implemented by it.Photos were taken with PV aS500 electronic portal imaging device (EPID) and actual position of leafs was determined by gradient algorithm to calculate the pass rate for leaf verification.MLC files were modified according to examination results and the plans were re-calculated while keeping other parameters unchanged.Thus,difference of targets and normal organs dose distribution before and after the appearance of leaf errors were obtained.Results The dose distribution of most organs after leaf errors were increased or decreased,and the maximum dose of spinal cord in the sixth and thirteen cases exceeded the limit of 45 Gy.In the group of simple plan only the changes of maximum dose to the spinal cord were statistically significant(t =-3.08,P ＜ 0.05),while in the group of the complex plan all changes of D95％ of PGTV and PTV,maximum dose of the spinal cord,V20 of lung and V40 of heart were statistically significant(t =-1.89,-1.99,-2.36,-2.55,-1.85,P ＜ 0.05).Conclusions To ensure the safety and effects,it was necessary to detect leaf position,particularly the complex intensity-modulated planning.Electronic portal imaging devices and treatment planning system could detect leaf positions during the implementation of a plan and obtain the actual dose of targets and normal organs.