摘要目的 建立利用半导体探测器阵列检测多叶准直器(MLC)叶片定位误差的方法,用于MLC的日常质量保证.方法 在MapCheck半导体探测器阵列上,相邻行探测器是错开半个探测器间距分布的.针对这种分布特点,设计了台阶式叶片位置模式,代替胶片测量常用的篱笆式(picket fence)叶片位置模式,作为叶片位置参考模式.在参考模式的基础上,人为引入不同大小的叶片位置误差,得到一组新的叶片位置模式--叶片位置校准模式.依次照射参考模式和校准模式,得到每一个探测器测量剂量与叶片位置误差的关系曲线.该曲线作为测量叶片位置误差的校准曲线.在进行NLC日常质量保证时,只需定期照射叶片位置参考模式,就可得到定量的叶片位置误差.结果 新方法在一个配置40对MLC的加速器上进行了测试(Elekta Precise).篱笆式叶片位置模式一次检测160个叶片位置,而台阶式叶片位置模式一次检测240个位置,检测效率提高50%;对于同样的1 mm叶片误差,前后两种模式的剂量变化分别是17%和25%,因此测量灵敏度提高8%.结论 建立了一种新的定量的MLC日常QA方法.通过重新设计叶片位置模式,新方法提高了实施效率和测量灵敏度.

abstractsObjective To design leaf patterns for Multileaf Collimator(MLC)routine quality assurance(OA)with a 2D diode array.Methods According to the detector distribution characteristic of the 2D diode array and basillg on the"picket fence"pattern,design the"stepwise"pattern.For each diode involving MLC QA,a calibration curve of relative output versus leaf positioning error was measured through delivering a set of patterns with different intentionally introduced positioning errors.When this proposed technique was delivered,the referenced patterns were exposed,and the calibration curves were used as a mean to quantitative determination of the leaf possible positioning errors through the detector readings.Results Compared with the"picket fence"pattern,the"stepwise"pattern not only had a high detecting efficiency,but also increased the dosimetric sensidvity to leaf positioning error.A 1 mm Ieaf positioni.error corresponds to a dose variation of 25% for the"stepwise"pattern,while for the"picket fence"pattern the same positioning error just causes a 17% dose vailation.Conclusions The new"stepwise"pattern is more efficient to be carried out,and more sensitive to sub-millimeter changes of leaf positioning.