利用胶片剂量拟合测量呼吸门控时间延迟

Film dose fitting for measuring time delay in respiratory gating

目的:通过对胶片剂量曲线的拟合来测量呼吸门控时间延迟,从而为临床治疗提供指导。方法:在呼吸门控治疗中使用模体带动胶片做周期运动,并提取相应的剂量曲线。然后使用Matlab软件模拟脉冲出束过程,根据每次脉冲出束形成的剂量曲线在胶片上的位置分布,计算出各像素点的累积剂量,从而得到在一个呼吸周期内形成的剂量曲线。比较不同呼吸门控延迟时间下的剂量曲线与胶片的实际剂量曲线,使用最小二乘法来寻找最优解,得到相应的门控时间延迟。结果:拟合胶片剂量曲线与实际剂量曲线有较好的一致性,开始出束时的门控延迟时间约为(252±20)ms,停止出束时的门控延迟时间约为(10±7)ms,开始出束时的门控延迟时间明显大于停止出束时的延迟时间。结论:基于胶片剂量拟合的方法可以精确地测量呼吸门控的时间延迟。对于任何门控设备,在临床使用前均需测试其门控延迟时间。

Objective To measure the time delay in respiratory gating by fitting the dose profiles of films,thereby providing a guidance for clinical treatment.Methods During respiratory gating treatment,the phantom was used to drive the films to perform periodic motion,and the corresponding dose profiles were extracted.Then Matlab software was used to simulate pulsed beam delivery.Based on the location distribution of the dose profiles formed by each pulsed beam delivery on film,the cumulative dose of each pixel was calculated for obtaining the dose profiles of a respiratory cycle.The dose profiles with different respiratory gating delay time was compared with the actual dose profiles,and the least square method was used to find the optimal solution,thereby obtaining the corresponding respiratory gating delay time.Results The fitted film dose profiles were in good agreement with the actual dose profiles.The average time delay for beam-on was greater than that of beam-off[(252±20)ms vs(10±7)ms].Conclusion The method based on film dose fitting can measure the time delay in respiratory gating accurately.For any gating devices,the time delay should be measured before clinical use.