Department of Radiation Oncology, Mayo Clinic, Phoenix, Arizona, USA.
Department of Radiation Oncology, Corewell Health Beaumont University Hospital, Royal Oak, Michigan, USA.
J Appl Clin Med Phys. 2024 Sep;25(9):e14486. doi: 10.1002/acm2.14486. Epub 2024 Aug 13.
The time structures of proton spot delivery in proton pencil beam scanning (PBS) radiation therapy are essential in many clinical applications. This study aims to characterize the time structures of proton PBS delivered by both synchrotron and synchrocyclotron accelerators using a non-invasive technique based on scattered particle tracking.
A pixelated semiconductor detector, AdvaPIX-Timepix3, with a temporal resolution of 1.56 ns, was employed to measure time of arrival of secondary particles generated by a proton beam. The detector was placed laterally to the high-flux area of the beam in order to allow for single particle detection and not interfere with the treatment. The detector recorded counts of radiation events, their deposited energy and the timestamp associated with the single events. Individual recorded events and their temporal characteristics were used to analyze beam time structures, including energy layer switch time, magnet switch time, spot switch time, and the scanning speeds in the x and y directions. All the measurements were repeated 30 times on three dates, reducing statistical uncertainty.
The uncertainty of the measured energy layer switch times, magnet switch time, and the spot switch time were all within 1% of average values. The scanning speeds uncertainties were within 1.5% and are more precise than previously reported results. The measurements also revealed continuous sub-milliseconds proton spills at a low dose rate for the synchrotron accelerator and radiofrequency pulses at 7 µs and 1 ms repetition time for the synchrocyclotron accelerator.
The AdvaPIX-Timepix3 detector can be used to directly measure and monitor time structures on microseconds scale of the PBS proton beam delivery. This method yielded results with high precision and is completely independent of the machine log files.
质子笔形束扫描（PBS）放射治疗中质子点传递的时间结构在许多临床应用中至关重要。本研究旨在使用基于散射粒子跟踪的非侵入性技术，对同步加速器和同步回旋加速器产生的质子 PBS 的时间结构进行特征描述。
采用时间分辨率为 1.56 ns 的像素化半导体探测器 AdvapiX-Timepix3 来测量质子束产生的次级粒子的到达时间。探测器放置在束的高通量区域的横向位置，以便进行单粒子检测，并且不会干扰治疗。探测器记录辐射事件的计数、它们的沉积能量以及与单个事件相关联的时间戳。单个记录的事件及其时间特性被用于分析束的时间结构，包括能量层切换时间、磁体切换时间、点切换时间以及 x 和 y 方向的扫描速度。在三个日期上重复进行了 30 次测量，以降低统计不确定性。
测量的能量层切换时间、磁体切换时间和点切换时间的不确定性均在平均值的 1%以内。扫描速度的不确定性在 1.5%以内，并且比以前报道的结果更加精确。测量结果还揭示了同步加速器中低剂量率下连续的亚毫秒质子脉冲，以及同步回旋加速器中 7 µs 和 1 ms 重复时间的射频脉冲。
AdvapiX-Timepix3 探测器可用于直接测量和监测 PBS 质子束传递的微秒级时间结构。该方法具有高精度的结果，并且完全独立于机器日志文件。
