Mount Vernon Cancer Centre, Northwood, UK.
Division of Cancer Sciences, Faculty of Biology Medicine and Health, University of Manchester, Manchester, UK.
Acta Oncol. 2023 Aug;62(8):923-931. doi: 10.1080/0284186X.2023.2238543. Epub 2023 Jul 24.
Delivered radiotherapy doses do not exactly match those planned for a course of treatment, largely due to inter-fraction changes in anatomy. In this study, accumulated delivered dose was calculated for a sample of cervical cancer patients, by deformably registering daily cone beam computed tomography (CBCT) images to the planning computed tomography (CT) scan. Planned and accumulated doses were compared for the clinical target volume (CTV), bladder, and rectum. For 10 patients receiving 45 Gy in 25 fractions of external beam radiotherapy, daily dose distributions were calculated on CBCT. These images were deformed onto the planning CT and the dose was accumulated using Velocity 4.1 (Varian Medical Systems, Palo Alto, USA). The quality of deformable image registration was evaluated visually and by calculating Dice similarity coefficients and mean distance to agreement. V95%>99% was achieved for the primary CTV in 9/10 patients for the planned dose distribution and 7/10 patients for the accumulated dose distribution. Primary CTV coverage by 95% of the prescription dose was reduced in one patient, due to an increase in anterior-posterior separation. Comparison of planned and accumulated dose volume histograms (DVHs) for the bladder and rectum found agreement within 5% at low and intermediate doses, but differences exceeded 20% at higher doses. Direct addition of CBCT DVHs was seen to be a poor estimate for the accumulated DVH at higher doses. Computation of delivered radiotherapy dose that accounts for inter-fraction anatomical changes is important for establishing dose-effect relationships. Updating delivered dose distributions after each fraction would support informed clinical decision making on any potential treatment interventions.
由于分次间解剖结构的变化，放射治疗的实际剂量与计划剂量并不完全匹配。在这项研究中，通过将每日锥形束 CT（CBCT）图像与计划 CT 扫描变形配准，计算了宫颈癌患者样本的累积递送剂量。比较了临床靶区（CTV）、膀胱和直肠的计划剂量和累积剂量。对于 10 名接受 45Gy、25 次分割外照射放疗的患者，在 CBCT 上计算了每日剂量分布。将这些图像变形到计划 CT 上，并使用 Velocity 4.1（美国瓦里安医疗系统公司）累积剂量。通过计算 Dice 相似系数和平均一致距离，对可变形图像配准的质量进行了视觉评估。在 10 名患者中，有 9 名患者的原发性 CTV 在计划剂量分布中达到了 95%>99%，7 名患者在累积剂量分布中达到了这一水平。由于前后分离增加，一名患者的原发性 CTV 接受 95%处方剂量的覆盖减少。比较膀胱和直肠的计划和累积剂量体积直方图（DVH）发现，在低剂量和中剂量时，两者之间的差异在 5%以内，但在高剂量时，差异超过 20%。在高剂量时，直接添加 CBCT DVH 被认为是累积 DVH 的一个较差估计。考虑分次间解剖变化的放射治疗实际剂量计算对于建立剂量-效应关系非常重要。在每分次后更新实际剂量分布将支持对任何潜在治疗干预措施进行知情的临床决策。
