King R B, Agnew C E, O'Connell B F, Prise K M, Hounsell A R, McGarry C K
Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, BT9 7AE, UK.
Phys Med Biol. 2016 Aug 7;61(15):5529-46. doi: 10.1088/0031-9155/61/15/5529. Epub 2016 Jul 6.
The aim of this work was to track and verify the delivery of respiratory-gated irradiations, performed with three versions of TrueBeam linac, using a novel phantom arrangement that combined the OCTAVIUS(®) SRS 1000 array with a moving platform. The platform was programmed to generate sinusoidal motion of the array. This motion was tracked using the real-time position management (RPM) system and four amplitude gating options were employed to interrupt MV beam delivery when the platform was not located within set limits. Time-resolved spatial information extracted from analysis of x-ray fluences measured by the array was compared to the programmed motion of the platform and to the trace recorded by the RPM system during the delivery of the x-ray field. Temporal data recorded by the phantom and the RPM system were validated against trajectory log files, recorded by the linac during the irradiation, as well as oscilloscope waveforms recorded from the linac target signal. Gamma analysis was employed to compare time-integrated 2D x-ray dose fluences with theoretical fluences derived from the probability density function for each of the gating settings applied, where gamma criteria of 2%/2 mm, 1%/1 mm and 0.5%/0.5 mm were used to evaluate the limitations of the RPM system. Excellent agreement was observed in the analysis of spatial information extracted from the SRS 1000 array measurements. Comparisons of the average platform position with the expected position indicated absolute deviations of <0.5 mm for all four gating settings. Differences were observed when comparing time-resolved beam-on data stored in the RPM files and trajectory logs to the true target signal waveforms. Trajectory log files underestimated the cycle time between consecutive beam-on windows by 10.0 ± 0.8 ms. All measured fluences achieved 100% pass-rates using gamma criteria of 2%/2 mm and 50% of the fluences achieved pass-rates >90% when criteria of 0.5%/0.5 mm were used. Results using this novel phantom arrangement indicate that the RPM system is capable of accurately gating x-ray exposure during the delivery of a fixed-field treatment beam.
这项工作的目的是使用一种将OCTAVIUS(®) SRS 1000阵列与移动平台相结合的新型体模装置，跟踪并验证使用三个版本的TrueBeam直线加速器进行的呼吸门控照射的实施情况。该平台被编程以产生阵列的正弦运动。使用实时位置管理（RPM）系统跟踪此运动，并采用四种幅度门控选项，以便在平台不在设定极限范围内时中断MV束流的输送。将从阵列测量的X射线注量分析中提取的时间分辨空间信息，与平台的编程运动以及X射线野输送期间RPM系统记录的轨迹进行比较。体模和RPM系统记录的时间数据，对照直线加速器在照射期间记录的轨迹日志文件以及从直线加速器靶信号记录的示波器波形进行验证。采用伽马分析将时间积分的二维X射线剂量注量与从应用的每种门控设置的概率密度函数导出的理论注量进行比较，其中使用2%/2毫米、1%/1毫米和0.5%/0.5毫米的伽马标准来评估RPM系统的局限性。在从SRS 1000阵列测量中提取的空间信息分析中观察到了极好的一致性。平均平台位置与预期位置的比较表明，对于所有四种门控设置，绝对偏差均<0.5毫米。在将RPM文件和轨迹日志中存储的时间分辨束流开启数据与真实靶信号波形进行比较时观察到了差异。轨迹日志文件将连续束流开启窗口之间的周期时间低估了10.0±0.8毫秒。使用2%/2毫米的伽马标准时，所有测量的注量通过率均达到100%，使用0.5%/0.5毫米的标准时，50%的注量通过率>90%。使用这种新型体模装置的结果表明，RPM系统能够在固定野治疗束的输送过程中准确地门控X射线照射。
