Department of Radiation Oncology, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands. Author to whom any correspondence should be addressed.
Phys Med Biol. 2020 Jul 31;65(15):155014. doi: 10.1088/1361-6560/ab91db.
Thoracic tumours are increasingly considered indications for pencil beam scanned proton therapy (PBS-PT) treatments. Conservative robustness settings have been suggested due to potential range straggling effects caused by the lung micro-structure. Using proton radiography (PR) and a 4D porcine lung phantom, we experimentally assess range errors to be considered in robust treatment planning for thoracic indications. A human-chest-size 4D phantom hosting inflatable porcine lungs and corresponding 4D computed tomography (4DCT) were used. Five PR frames were planned to intersect the phantom at various positions. Integral depth-dose curves (IDDs) per proton spot were measured using a multi-layer ionisation chamber (MLIC). Each PR frame consisted of 81 spots with an assigned energy of 210 MeV (full width at half maximum (FWHM) 8.2 mm). Each frame was delivered five times while simultaneously acquiring the breathing signal of the 4D phantom, using an ANZAI load cell. The synchronised ANZAI and delivery log file information was used to retrospectively sort spots into their corresponding breathing phase. Based on this information, IDDs were simulated by the treatment planning system (TPS) Monte Carlo dose engine on a dose grid of 1 mm. In addition to the time-resolved TPS calculations on the 4DCT phases, IDDs were calculated on the average CT. Measured IDDs were compared with simulated ones, calculating the range error for each individual spot. In total, 2025 proton spots were individually measured and analysed. The range error of a specific spot is reported relative to its water equivalent path length (WEPL). The mean relative range error was 1.2% (1.5 SD 2.3 %) for the comparison with the time-resolved TPS calculations, and 1.0% (1.5 SD 2.2 %) when comparing to TPS calculations on the average CT. The determined mean relative range errors justify the use of 3% range uncertainty for robust treatment planning in a clinical setting for thoracic indications.
胸部肿瘤越来越多地被认为是铅笔束扫描质子治疗（PBS-PT）治疗的适应证。由于肺部微结构引起的潜在射程离散效应，建议采用保守的稳健性设置。我们使用质子射线照相术（PR）和 4D 猪肺体模，从实验上评估了胸部适应证中稳健治疗计划中需要考虑的射程误差。使用了一个具有可膨胀猪肺和相应的 4D 计算机断层扫描（4DCT）的人体胸部大小 4D 体模。计划在不同位置的体模上相交五个 PR 帧。使用多层电离室（MLIC）测量每个质子点的积分深度剂量曲线（IDD）。每个 PR 帧由 81 个点组成，分配能量为 210 MeV（半最大值全宽（FWHM）为 8.2mm）。每次传送五个 PR 帧，同时获取 4D 体模的呼吸信号，使用 ANZAI 称重传感器。同步的 ANZAI 和传送日志文件信息用于将点追溯到它们相应的呼吸相位。根据该信息，TPS 蒙特卡罗剂量引擎在剂量网格为 1mm 的情况下模拟 IDD。除了在 4DCT 相位上进行时间分辨的 TPS 计算外，还在平均 CT 上计算 IDD。将测量的 IDD 与模拟的 IDD 进行比较，计算每个单独点的射程误差。总共单独测量和分析了 2025 个质子点。特定点的射程误差相对于其水当量路径长度（WEPL）报告。与时间分辨的 TPS 计算相比，平均相对射程误差为 1.2%（1.5 SD 2.3%），与平均 CT 上的 TPS 计算相比，平均相对射程误差为 1.0%（1.5 SD 2.2%）。确定的平均相对射程误差证明，在临床情况下为胸部适应证进行稳健治疗计划时，使用 3%的射程不确定性是合理的。
