Department of Radiation Oncology, University of California San Diego, La Jolla, CA, USA.
Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Göteborg, Sweden.
J Appl Clin Med Phys. 2020 Mar;21(3):153-161. doi: 10.1002/acm2.12841. Epub 2020 Mar 14.
The purpose of this study of pancreatic cancer patients treated with respiratory-guided stereotactic body radiotherapy (SBRT) on a standard linac was to investigate (a) the intrafractional relationship change (IRC) between a breathing signal and the tumor position, (b) the impact of IRC on the delivered dose, and (c) potential IRC predictors.
We retrospectively investigated 10 pancreatic cancer patients with 2-4 implanted fiducial markers in the tumor treated with SBRT. Fluoroscopic images were acquired before and after treatment delivery simultaneously with the abdominal breathing motion. We quantified the IRC as the change in fiducial location for a given breathing amplitude in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions from before to after treatment delivery. The treatment plans were re-calculated after changing the isocenter coordinates according to the IRCs. Four treatment- or patient-related factors were investigated as potential predictors for IRC using linear models.
The average (±1 SD) absolute IRCs in the LR, AP, and SI directions were 1.2 ± 1.2 mm, 0.7 ± 0.7 mm, and 1.1 ± 0.8 mm, respectively. The average 3D IRC was 2.0 ± 1.3 mm (range: 0.4-5.3 mm) for a median treatment delivery time of 8.5 min (range: 5.7-19.9 min; n = 31 fractions). The dose coverage of the internal target volume (ITV) decreased by more than 3% points in three of 31 fractions. In those cases, the 3D IRC had been larger than 4.3 mm. The 3D IRC was found to correlate with changes in the minimum breathing amplitude during treatment delivery.
On average, 2 mm of treatment delivery accuracy was lost due to IRC. Periodical intrafractional imaging is needed to safely deliver respiratory-guided SBRT.
本研究旨在探讨在标准直线加速器上对接受呼吸引导立体定向体放射治疗（SBRT）的胰腺癌患者进行的研究：（a）呼吸信号与肿瘤位置之间的分次内相关性变化（IRC）；（b）IRC 对所给予剂量的影响；（c）潜在的 IRC 预测因子。
我们回顾性研究了 10 例胰腺肿瘤患者，这些患者在肿瘤中植入了 2-4 个基准标记物，采用 SBRT 进行治疗。在治疗前后，与腹部呼吸运动同时采集荧光透视图像。我们将 IRC 定义为从治疗前到治疗后，在给定呼吸幅度下，基准标记物在左右（LR）、前后（AP）和上下（SI）方向上的位置变化。根据 IRC 改变等中心点坐标后，重新计算治疗计划。使用线性模型研究了四个与治疗或患者相关的因素，作为 IRC 的潜在预测因子。
LR、AP 和 SI 方向上的平均（±1 SD）IRC 绝对值分别为 1.2±1.2mm、0.7±0.7mm 和 1.1±0.8mm。中位治疗时间为 8.5 分钟（范围：5.7-19.9 分钟；n=31 个分次）时，平均 3D IRC 为 2.0±1.3mm（范围：0.4-5.3mm）。在 31 个分次中有 3 个分次的 ITV 剂量覆盖率降低超过 3 个百分点，这 3 个分次的 3D IRC 大于 4.3mm。发现 3D IRC 与治疗过程中最小呼吸幅度的变化相关。
平均而言，由于 IRC 导致 2mm 的治疗输送精度损失。需要定期进行分次内成像，以安全地进行呼吸引导 SBRT。
