Purpose

To evaluate absolute dose between phase- and amplitude-gated modes for lung stereotactic body radiation therapy (SBRT), using the moving targets developed in-house.

Methods

The moving targets were developed in-house, allowing measurements of absolute dose using Semiflex ion chamber, Pinpoint ion chamber and microDiamond detector. 24 plans were generated in the Pinnacle 16.2 treatment planning system (TPS). 720 partial dynamic conformal arcs (DCA), 120 for phase- and 120 for amplitude-gated mode per detector, were performed to compare dose discrepancy (planned vs measured doses), for all detectors. Single fraction of 15 Gy was delivered with TrueBeam Novalis STx, triggered on the stable phases (phase-gated mode) or near the end-exhalation (amplitude-gated mode), for a breathing period ranging from 2 s to 7 s, using flattened filter free beams (FFF).

Results

The lowest discrepancy between measured and planned dose was obtained using the microDiamond detector in the phase-gated −0.1 (−0.2 to 0) % and −0.3 (−0.4 to −0.1) % in amplitude-gated mode (p < 0.001). Using PinPoint ion chamber, greater discrepancy was obtained in phase-gated −0.5 (−0.7 to −0.3) %, comparing to the amplitude-gated mode −0.1 (−0.2 to 0) % (p < 0.001). The greatest discrepancy was observed using the Semiflex ion chamber, with lesser differences between the phase-gated 1.5 (1.2–1.7) % and amplitude-gated mode 1.4 (1.2–1.5) (p = 0.134).

Conclusion

Detectors with low discrepancy, PinPoint ion chamber and microDiamond detectors, can be used in routine quality assurance for lung gated delivery in SBRT treatment, for commercial phantom as for phantom developed in-house.

中文翻译：

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肺门控递送立体定向放射治疗的绝对剂量测量

目的

使用内部开发的移动目标评估肺立体定向放射治疗 (SBRT) 的相位和幅度门控模式之间的绝对剂量。

方法

移动目标是内部开发的，允许使用 Semiflex 离子室、Pinpoint 离子室和 microDiamond 检测器测量绝对剂量。在 Pinnacle 16.2 治疗计划系统 (TPS) 中生成了 24 个计划。每个探测器执行 720 个部分动态保形弧 (DCA)，120 个用于相位门控模式，120 个用于幅度门控模式，以比较所有探测器的剂量差异（计划剂量与测量剂量）。使用 TrueBeam Novalis STx 在稳定阶段（相位门控模式）或接近呼气末期（幅度门控模式）触发，呼吸周期为 2 秒到 7 秒，使用扁平化过滤自由光束 (FFF)。

结果

在相位门控 -0.1（-0.2 至 0）% 和 -0.3（-0.4 至 -0.1）% 幅度门控模式下，使用 microDiamond 检测器获得测量剂量和计划剂量之间的最低差异（p < 0.001）。使用 PinPoint 离子室，与振幅门控模式 -0.1 (-0.2 至 0) % (p < 0.001) 相比，相位门控 -0.5 (-0.7 至 -0.3) % 的差异更大。使用 Semiflex 离子室观察到最大的差异，相位门控 1.5 (1.2–1.7) % 和幅度门控模式 1.4 (1.2–1.5) (p = 0.134) 之间的差异较小。

结论

具有低差异的检测器、PinPoint 离子室和 microDiamond 检测器可用于 SBRT 治疗中肺门控递送的常规质量保证、商业体模和内部开发的体模。