Department of Radiation Oncology, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands.
Division for Medical Radiation Physics, Carl von Ossietzky Universität Oldenburg, Oldenburg, Germany.
Med Phys. 2021 Mar;48(3):1372-1380. doi: 10.1002/mp.14713. Epub 2021 Feb 6.
The capability of proton therapy to provide highly conformal dose distributions is impaired by range uncertainties. The aim of this work is to apply range probing (RP), a form of a proton radiography-based quality control (QC) procedure for range accuracy assessment in head and neck cancer (HNC) patients in a clinical setting.
This study included seven HNC patients. RP acquisition was performed using a multi-layer ionization chamber (MLIC). Per patient, two RP frames were acquired within the first two weeks of treatment, on days when a repeated CT scan was obtained. Per RP frame, integral depth dose (IDD) curves of 81 spots around the treatment isocenter were acquired. Range errors are determined as a discrepancy between calculated IDDs in the treatment planning system and measured residual ranges by the MLIC. Range errors are presented relative to the water equivalent path length of individual proton spots. In addition to reporting results for complete measurement frames, an analysis, excluding range error contributions due to anatomical changes, is presented.
Discrepancies between measured and calculated ranges are smaller when performing RP calculations on the day-specific patient anatomy rather than the planning CT. The patient-specific range evaluation shows an agreement between calculated and measured ranges for spots in anatomically consistent areas within 3% (1.5 standard deviation).
The results of an RP-based QC procedure implemented in the clinical practice for HNC patients have been demonstrated. The agreement of measured and simulated proton ranges confirms the 3% uncertainty margin for robust optimization. Anatomical variations show a predominant effect on range accuracy, motivating efforts towards the implementation of adaptive radiotherapy.
质子治疗提供高度适形剂量分布的能力因射程不确定性而受损。本研究旨在应用射程探测（RP），这是一种基于质子射线照相的质量控制（QC）程序，用于在临床环境中对头颈部癌症（HNC）患者的射程准确性进行评估。
本研究包括 7 名 HNC 患者。使用多层电离室（MLIC）进行 RP 采集。对于每位患者，在治疗的前两周内，当获得重复 CT 扫描时，采集两个 RP 帧。对于每个 RP 帧，在治疗等中心点周围的 81 个点处获取积分深度剂量（IDD）曲线。射程误差被确定为治疗计划系统中计算的 IDD 与 MLIC 测量的剩余射程之间的差异。射程误差相对于单个质子点的水等效路径长度呈现。除了报告完整测量帧的结果外，还提出了一种分析方法，该方法排除了由于解剖结构变化引起的射程误差贡献。
在针对特定患者解剖结构而不是计划 CT 进行 RP 计算时，测量和计算的射程之间的差异较小。针对解剖结构一致区域内的点进行的患者特异性射程评估显示，计算和测量的射程之间的一致性在 3%（1.5 标准差）以内。
已经证明了对头颈部癌症患者实施的基于 RP 的 QC 程序的结果。测量和模拟质子射程的一致性证实了稳健优化的 3%不确定性余量。解剖变异对射程准确性有主要影响，这促使人们努力实施自适应放疗。
