Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA.
Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA.
J Appl Clin Med Phys. 2021 May;22(5):175-181. doi: 10.1002/acm2.13234. Epub 2021 Mar 29.
Radixact Synchrony corrects for target motion during treatment by adjusting the jaw and MLC positions in real time. As the jaws move off axis, Synchrony attempts to adjust for a loss in output due to the un-flattened 6 MV beam by increasing the jaw aperture width. The purpose of this work was to assess the impact of the variable-width aperture on delivered dose using measurements and simulations.
Longitudinal beam profile measurements were acquired using an Edge diode with static gantry. Jaw-offset peak, width, and integral factors were calculated for profiles with the jaws in the extreme positions using both variable-width (Synchrony) and fixed-width apertures. Treatment plans with target motion and compensation were compared to planned doses to study the impact of the variable aperture on volumetric dose.
The jaw offset peak factor (JOPF) for the Synchrony jaw settings were 0.964 and 0.983 for the 1.0- and 2.5-cm jaw settings, respectively. These values decreased to 0.925 and 0.982 for the fixed-width settings, indicating that the peak value of the profile would decrease by 7.5% compared to centered if the aperture width was held constant. The IMRT dose distributions reveal similar results, where gamma pass rates are above tolerance for the Synchrony jaw settings but fall significantly for the fixed-width 1-cm jaws.
The variable-width behavior of Synchrony jaws provides a larger output correction for the 1-cm jaw setting. Without the variable-aperture correction, plans with the 1-cm jaw setting would underdose the target if the jaws spend a significant amount of time in the extreme positions. This work investigated the change in delivered dose with jaws in the extreme positions, therefore overall changes in dose due to offset jaws are expected to be less for composite treatment deliveries.
Radixact Synchrony 通过实时调整颌骨和 MLC 位置来校正治疗中的靶区运动。当颌骨偏离轴线时，Synchrony 试图通过增加颌骨开口宽度来调整由于未扁平化 6 MV 射束而导致的输出损失。这项工作的目的是使用测量和模拟评估可变宽度孔径对剂量分布的影响。
使用带有静态旋转架的 Edge 二极管进行纵向射束轮廓测量。对于处于极端位置的颌骨，使用可变宽度（Synchrony）和固定宽度孔径分别计算了轮廓的颌骨偏移峰值、宽度和积分因子。对于有靶区运动和补偿的治疗计划，与计划剂量进行了比较，以研究可变孔径对容积剂量的影响。
Synchrony 颌骨设置的颌骨偏移峰值因子（JOPF）分别为 1.0 和 2.5 cm 颌骨设置的 0.964 和 0.983。对于固定宽度设置，这些值分别降低到 0.925 和 0.982，这表明如果孔径宽度保持不变，与中心相比，轮廓的峰值将降低 7.5%。调强放疗剂量分布显示出类似的结果，其中对于 Synchrony 颌骨设置，伽玛通过率高于公差，但对于固定宽度 1 cm 颌骨则显著下降。
Synchrony 颌骨的可变宽度行为为 1 cm 颌骨设置提供了更大的输出校正。如果颌骨在极端位置花费大量时间，没有可变孔径校正，使用 1 cm 颌骨设置的计划将导致靶区剂量不足。这项工作研究了在颌骨处于极端位置时剂量分布的变化，因此，由于偏移颌骨引起的总剂量变化预计在复合治疗输送中会更小。
