Objective: Because of the high dose rate ,long beam on time and lower using efficiency of beam,the target of to-motherapy system degradate faster than other linac system. Also it is a complicated and time-consuming work to replace the target. So it is necessary to monitor the degradation of the target in order to make sure the right time to replace the target. The objective of this paper is to find out an effective and easy method to monitor the target degradation. Methods: From March, 2010 to January,2012 we insisted to trace the target degradation of a HiART system by doing a rotational variation procedure once a week at least. Then we analyzed these RUAT data using two methods to monitor the target degradation. The first was to check the lateral profile curve pulse by pulse recommended by manufacturer. The second was the double ionchamber dose rate comparison method which was developed in this paper. Results: The double ionchamber dose rate comparison method developed in this paper is an effective method not only when the target wearied out normally, but also the target stopped rotating or wearied out evenly,which is better than pulse by pulse lateral profile variation method. Also we have discussed the effect factors and given the value to make sure the time to replace the target when using the double ionchamber dose rate comparison method. Conclusions: The double ionchamber dose rate comparison method is an effective,tried and easy method for monitoring the target degradation.%目的:螺旋断层放疗系统由于其高剂量率、出束时间长和对射线的利用率相对较低等原因,导致它的靶是一个易损耗部件,需要及时更换.同时,换靶的工序复杂耗时,需要合理的安排换靶时机,避免影响患者治疗计划的执行.本文的目标为寻找一种有效且简单的监测靶损耗的方法,以确定及时合理的换靶时机.方法:通过对螺旋断层放疗系统靶相关的文献调研以及实际工作经验总结,发展了一种利用系统自带的监测电离室数据检测靶损耗的名为双电离室剂量率比较法的监测靶损耗的方法.进而,通过对一台螺旋断层放疗系统从2010年3月至2012年1月的追踪监测,每周至少采集一次在空气中的旋转变化程序(Rotational Variation Procedure,简称RUAT)数据,用本文发展的双电离室剂量率比较法对数据进行分析,验证此方法在监测靶的损耗时的有效性.同时,也对厂家推荐的逐脉冲横向剖面曲线变化法的有效性进行了检验.结果:本文发展的双电离室剂量率比较法能监测靶损耗的状况,在靶停转或非常均匀的损耗时,厂家推荐的办法会失效,本文采取的办法依然有效.同时对双电离室剂量率比较法的影响因素进行了分析,并给出了临床换靶的参考条件.结论:本文寻找的双电离室剂量率比较法是一种简单易行、可靠有效的监测靶损耗的方法.
展开▼
