Khalifa Mateb Al, Ma Tianjun, Aljuaid Haya, Kim Siyong, Song William Y
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia, USA.
J Appl Clin Med Phys. 2025 Jul;26(7):e70116. doi: 10.1002/acm2.70116. Epub 2025 May 13.
This study aims to evaluate how different gantry angles, breathing rates (BPM), cine image speeds, and tracking algorithms affect beam on/off latency and the subsequent impact on target dose for a 0.35T MR-Linac with a 6 MV FFF beam. The investigation incorporates an image-based MRI4D modus QA motion phantom (MQA) and a measurement-based plastic scintillation detector (PSD).
The MQA's target was customized with an insertion for a 1 mm PSD from BluePhysics. Both the PSD and the MQA were simultaneously synchronized to the Linac to capture latency signals. A plan was created in the ViewRay TPS to deliver dose to the target at three gantry angles (0°, 120°, and 240°). Each gantry angle was evaluated at three breathing rates (10, 12, and 15 BPM). The study also examined two imaging speeds (4 and 8 FPS) and four tracking algorithms.
Across all configurations at 4 FPS, the overall mean beam-on latency was 0.339 ± 0.06 s from the PSD and 0.318 ± 0.06 s from the MQA, whereas at 8 FPS it was 0.630 ± 0.07 s (PSD) and 0.609 ± 0.07 s (MQA). Conversely, the overall mean beam-off latency at 4 FPS was 0.153 ± 0.03 s (PSD) and 0.124 ± 0.03 s (MQA), while at 8 FPS it was 0.121 ± 0.06 s (PSD) and 0.205 ± 0.04 s (MQA). The overall mean difference between gating and non-gating doses was an increase of 12.050 ± 9.2 cGy at 4 FPS and 14.044 ± 7.4 cGy at 8 FPS.
This comprehensive study underscores the significant influence of gantry angle, breathing rate, cine imaging speed, and tracking algorithms on latency and dose delivery accuracy in a 0.35T MR-Linac.
本研究旨在评估不同的机架角度、呼吸频率（每分钟呼吸次数，BPM）、电影图像速度和跟踪算法如何影响配备6 MV FFF束流的0.35T MR直线加速器的束流开启/关闭延迟以及对靶区剂量的后续影响。该研究纳入了基于图像的MRI4D模式质量保证运动体模（MQA）和基于测量的塑料闪烁探测器（PSD）。
使用BluePhysics公司的1毫米PSD插入件对MQA的靶区进行定制。PSD和MQA均与直线加速器同时同步，以捕获延迟信号。在ViewRay治疗计划系统（TPS）中创建一个计划，在三个机架角度（0°、120°和240°）向靶区输送剂量。每个机架角度在三种呼吸频率（10、12和15 BPM）下进行评估。该研究还考察了两种成像速度（4和8帧每秒，FPS）和四种跟踪算法。
在4 FPS的所有配置中，PSD测得的总体平均束流开启延迟为0.339±0.06秒，MQA测得的为0.318±0.06秒；而在8 FPS时，PSD测得的为0.630±0.07秒，MQA测得的为0.609±0.07秒。相反，4 FPS时的总体平均束流关闭延迟，PSD测得的为0.153±0.03秒，MQA测得的为0.124±0.03秒；8 FPS时，PSD测得的为0.121±0.06秒，MQA测得的为0.205±0.04秒。门控剂量与非门控剂量之间的总体平均差异在4 FPS时增加了12.050±9.2 cGy，在8 FPS时增加了14.044±7.4 cGy。
这项全面的研究强调了机架角度、呼吸频率、电影成像速度和跟踪算法对0.35T MR直线加速器的延迟和剂量输送准确性有重大影响。
