Abstract：
Objective.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.Approach.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.Main results.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.Significance.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.
摘要：
目的：＆＃xD;在质子铅笔束扫描（PBS）连续传递中，光束被连续地传递而没有斑点之间的中断。对于基于同步加速器的系统，提取的束流表现出溢出结构，和最近关于束电流测量的出版物已经证明了围绕标称值的显著波动。这些波动潜在地导致与假设稳定的射束电流计算的那些的剂量偏差。这项研究调查了质子PBS连续扫描过程中这种束电流波动的剂量学含义。＆＃xD;方法：＆＃xD;使用代表性的临床质子PBS计划，我们进行了模拟，以模拟最坏情况下的临床分娩环境，其中束流的变化范围为标称值的50％至250％。模拟使用了针对佛罗里达州梅奥诊所即将推出的粒子治疗系统的最佳光束递送效率而优化的光束递送参数。我们重建了模拟的递送剂量分布，并评估了束流波动的剂量测定影响。＆＃xD;主要结果：＆＃xD;尽管显着的束电流波动导致每个光斑水平的偏差，总体剂量分布与假设束流稳定的情况几乎相同。所有计划的1mm/1%Gamma合格率均为100%。在PTVDVH中观察到小于0.2%的均方根误差(RMSE)。在所有剂量学评估指标中观察到最小差异。＆＃xD;意义：＆＃xD;我们的发现表明，通过我们的波束输送系统和临床计划实践，而显著的束电流波动可能导致在每个点水平的大的局部移动MU偏差，对剂量分布的总体影响是最小的。
.
