Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States of America.
Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, TX 77030, United States of America.
Phys Med Biol. 2024 Jul 17;69(15). doi: 10.1088/1361-6560/ad56f2.
We previously proposed range-guided adaptive proton therapy (RGAPT) that uses mid-range treatment beams as probing beams and intra-fractionated range measurements for online adaptation. In this work, we demonstrated experimental verification and reported the dosimetric accuracy for RGAPT. A STEEV phantom was used for the experiments, and a 3 × 3 × 3 cmcube inside the phantom was assigned to be the treatment target. We simulated three online range shift scenarios: reference, overshoot, and undershoot, by placing upstream Lucite sheets, 4, 0, and 8 that corresponded to changes of 0, 6.8, and -6.8 mm, respectively, in water-equivalent path length. The reference treatment plan was to deliver single-field uniform target doses in pencil beam scanning mode and generated on the Eclipse treatment planning system. Different numbers of mid-range layers, including single, three, and five layers, were selected as probing beams to evaluate beam range (BR) measurement accuracy in positron emission tomography (PET). Online plans were modified to adapt to BR shifts and compensate for probing beam doses. In contrast, non-adaptive plans were also delivered and compared to adaptive plans by film measurements. The mid-range probing beams of three (5.55MU) and five layers (8.71MU) yielded accurate range shift measurements in 60 s of PET acquisition with uncertainty of 0.5 mm while the single-layer probing (1.65MU) was not sufficient for measurements. The adaptive plans achieved an average gamma (2%/2 mm) passing rate of 95%. In contrast, the non-adaptive plans only had an average passing rate of 69%. RGAPT planning and delivery are feasible and verified by the experiments. The probing beam delivery, range measurements, and adaptive planning and delivery added a small increase in treatment delivery workflow time but resulted in substantial dose improvement. The three-layer mid-range probing was most suitable considering the balance of high range measurement accuracy and the low number of probing beam layers.
我们之前提出了基于范围引导的自适应质子治疗（RGAPT），该方法使用中程治疗束作为探测束，并进行分次内范围测量以进行在线自适应调整。在这项工作中，我们进行了实验验证，并报告了 RGAPT 的剂量学准确性。使用 STEEV 体模进行实验，体模内的 3×3×3cm³区域被指定为治疗靶区。我们通过放置上游 Lucite 板模拟了三种在线范围偏移场景：参考、过冲和欠冲，对应的水等效路径长度变化分别为 0、6.8 和-6.8mm。参考治疗计划是在笔形束扫描模式下均匀地给予单一靶区剂量，该计划是在 Eclipse 治疗计划系统上生成的。选择了单层、三层和五层等不同数量的中程层作为探测束，以评估正电子发射断层扫描（PET）中的光束范围（BR）测量准确性。在线计划进行了修改以适应 BR 偏移并补偿探测束剂量。相比之下，还进行了非自适应计划，并通过胶片测量与自适应计划进行了比较。在 60s 的 PET 采集时间内，三层（5.55MU）和五层（8.71MU）的中程探测束可实现准确的范围偏移测量，其不确定性为 0.5mm，而单层探测束（1.65MU）则不足以进行测量。自适应计划的平均伽马（2%/2mm）通过率为 95%。相比之下，非自适应计划的平均通过率仅为 69%。RGAPT 的计划和实施是可行的，并通过实验得到了验证。探测束的传递、范围测量以及自适应的计划和传递虽然增加了治疗实施流程的时间，但大大提高了剂量分布。考虑到高范围测量精度和低探测束层数之间的平衡，三层中程探测束是最合适的。
