一种关于RPM放疗呼吸门控系统束流时间延迟性能的参考质控方法

目的：提出一种关于RPM放疗呼吸门控系统束流时间延迟性能的参考质控方法，给出参考条件下VB与EDGE加速器的时间延迟测量结果。方法：首先设计梯形质控呼吸曲线并加载运动模体，利用定位CT扫描由运动模体驱动的W-L模体，然后设计用于束流出束和截止延迟测量的两类质控计划，最后在加速器上执行质控计划，使用EPID采集模体的静态参考图像与运动测量图像，通过分析致密金属球在运动图像和参考图像中的位置差，反推束流的时间延迟，分别在VB与EDGE两台加速器上做方法验证。结果：VB与EDGE加速器的束流出束时间延迟均小于100 ms，截止时间延迟基本一致，VB加速器约为14 ms,EDGE约为22 ms。10FFF各剂量率的出束时间延迟基本一致，而6FFF、6 MV和10 MV则随剂量率的变化略有增加。4个能量各剂量率的束流截止时间延迟均较小且相对一致，部分能量有随剂量率变大而延迟缩小的趋势。结论：本研究提出的RPM束流时间延迟参考质控方法和条件具有较高的测量可信度和较强的临床实操性，测量结果表明RPM呼吸门控系统响应灵敏，研究结果为呼吸门控系统的时间延迟质控提供了重要的方法学指导与数据参考。

Reference quality assurance method for beam time delay of RPM respiratory gating system for radiotherapy

Abstract: Objective To propose a reference quality assurance (QA) method for beam time delay of RPM respiratory-gated radiotherapy, and provide the measurement results of time delay on VB and EDGE accelerators under reference conditions. Methods A trapezoidal QA breathing curve was designed and loaded into motion phantom, and a W-L phantom driven by motion phantom was scanned with CT. Two types of QA plans which were designed for beam on and off time delay measurements were executed on accelerator, and EPID was used to acquire static reference images and motion images of phantom. The time delay was reversed by analyzing the position deviations of metal ball in motion and reference images. The proposed method was verified on VB and EDGE accelerators. Results The beam on time delay on VB and EDGE accelerators was less than 100 ms, and the beam off time delay on VB was close to that of EDGE (14 ms vs 22 ms). The beam on time delay of 10FFF was almost the same at each dose rate, while the beam on time delay of 6FFF, 6 MV and 10 MV was increased slightly with dose rate. The beam off time delay at each dose rate and 4 energies were small and relatively consistent. Except 10FFF, the time delay has s a tendency to decrease over the increase of the dose rate. Conclusion The proposed method and conditions for RPM time delay measurement have high measurement reliability and clinical practicality, and the RPM respiratory gating system exhibited fast response. This study provides significant methodology and reference data for quality assurance of respiratory gating system.