Liu Chunbo, Furutani Keith M, Shen Jiajian, Wan Chan Tseung Hok, Tan Hong Qi, Li Heng, Whitaker Thomas J, Beltran Chris J, Liang Xiaoying
Department of Radiation Oncology, Mayo Clinic, Jacksonville, FL, United States of America.
Department of Radiation Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, People's Republic of China.
Phys Med Biol. 2024 Jun 28;69(13). doi: 10.1088/1361-6560/ad56f6.
In proton pencil beam scanning (PBS) continuous delivery, the beam is continuously delivered without interruptions between spots. For synchrotron-based systems, the extracted beam current exhibits a spill structure, and recent publications on beam current measurements have demonstrated significant fluctuations around the nominal values. These fluctuations potentially lead to dose deviations from those calculated assuming a stable beam current. This study investigated the dosimetric implications of such beam current fluctuations during proton PBS continuous scanning.Using representative clinical proton PBS plans, we performed simulations to mimic a worst-case clinical delivery environment with beam current varies from 50% to 250% of the nominal values. The simulations used the beam delivery parameters optimized for the best beam delivery efficiency of the upcoming particle therapy system at Mayo Clinic Florida. We reconstructed the simulated delivered dose distributions and evaluated the dosimetric impact of beam current fluctuations.Despite significant beam current fluctuations resulting in deviations at each spot level, the overall dose distributions were nearly identical to those assuming a stable beam current. The 1 mm/1% Gamma passing rate was 100% for all plans. Less than 0.2% root mean square error was observed in the planning target volume dose-volume histogram. Minimal differences were observed in all dosimetric evaluation metrics.Our findings demonstrate that with our beam delivery system and clinical planning practice, while significant beam current fluctuations may result in large local move monitor unit deviations at each spot level, the overall impact on the dose distribution is minimal.
在质子笔形束扫描（PBS）连续照射中，束流在各点之间连续照射而无中断。对于基于同步加速器的系统，引出的束流呈现出脉冲结构，并且最近关于束流测量的出版物表明，其在标称值附近存在显著波动。这些波动可能导致剂量与假设束流稳定时计算出的剂量产生偏差。本研究调查了质子PBS连续扫描期间此类束流波动对剂量学的影响。
使用具有代表性的临床质子PBS计划，我们进行了模拟，以模拟束流在标称值的50%至250%之间变化的最坏情况临床照射环境。模拟使用了为佛罗里达州梅奥诊所即将投入使用的粒子治疗系统的最佳束流传输效率而优化的束流传输参数。我们重建了模拟的照射剂量分布，并评估了束流波动对剂量学的影响。
尽管束流的显著波动导致每个点水平出现偏差，但总体剂量分布与假设束流稳定时的分布几乎相同。所有计划的1毫米/1%伽马通过率均为100%。在计划靶区剂量体积直方图中观察到的均方根误差小于0.2%。在所有剂量学评估指标中观察到的差异极小。
我们的研究结果表明，对于我们的束流传输系统和临床计划实践，虽然显著的束流波动可能导致每个点水平出现较大的局部运动监测单位偏差，但对剂量分布的总体影响极小。
