Ciarmatori Alberto, Maffei Nicola, Mistretta Grazia Maria, Ceroni Paola, Bernabei Annalisa, Meduri Bruno, D'Angelo Elisa, Bruni Alessio, Giacobazzi Patrizia, Lohr Frank, Guidi Gabriele
Deptartment of Medical Physics, A.O. Ospedali Riuniti Marche Nord, Pesaro, Italy.
Department of Medical Physics, A.O. U. di Modena, Modena, Italy; Post Graduate School in Medical Physics, University of Turin, Turin, Italy.
Med Dosim. 2019;44(4):379-384. doi: 10.1016/j.meddos.2019.02.002. Epub 2019 Mar 12.
Parotid gland (PG) shrinkage and neck volume reduction during radiotherapy of head and neck (H&N) cancer patients is a clinical issue that has prompted interest in adaptive radiotherapy (ART). This study focuses on the difference between planned dose and delivered dose and the possible effects of an efficient replanning strategy during the course of treatment. Six patients with H&N cancer treated by tomotherapy were retrospectively enrolled. Thirty daily dose distributions (D) were calculated on pretreatment megavoltage computed tomography (MVCT) scans. Deformable Image Registration which matched daily MVCT with treatment planning kilovoltage computed tomography was performed. Using the resulting deformation vector field, all daily D were deformed to the planning kilovoltage computed tomography and resulting doses were accumulated voxel per voxel. Cumulative D was compared to planned dose distribution performing γ-analysis (2 mm, 2% of 2.2 Gy). Two single-intervention ART strategies were executed on the 18th fraction whose previous data had suggested to be a suitable timepoint for a single replanning intervention: (1) replanning on the original target and deformed organ at risks (OARs) (a "safer" approach regarding tumor coverage) and (2) replanning on both deformed target and deformed OARs. D showed differences between planned and delivered doses (3D-γ 2mm/2%-passing rate = 85 ± 1%, p < 0.001). Voxel by voxel dose accumulation showed an increase in average dose of warped PG of 3.0 Gy ± 3.3 Gy. With ART the average dose of warped PG decreased by 3.2 Gy ± 1.7 Gy in comparison to delivered dose without replanning when both target and OARs were deformed. Average dose of warped PG decreased by 2.0 Gy ± 1.4 Gy when only OARs were deformed. Anatomical variations lead to increased doses to PGs. Efficient single-intervention ART-strategies with replanning on the 18th MVCT result a reduced PG dose. A strategy with deformation of both target and OAR resulted in the lowest PG dose, while formally maintaining PTV coverage. Deformation of only OAR nevertheless reduces PG dose and has less uncertainties regarding PTV coverage.
头颈部（H&N）癌症患者在放疗期间腮腺（PG）萎缩和颈部体积减小是一个临床问题，这引发了人们对自适应放疗（ART）的兴趣。本研究聚焦于计划剂量与实际交付剂量之间的差异以及治疗过程中有效重新计划策略可能产生的影响。回顾性纳入了6例接受断层放疗的H&N癌症患者。在治疗前的兆伏级计算机断层扫描（MVCT）上计算30次每日剂量分布（D）。进行了将每日MVCT与治疗计划千伏级计算机断层扫描相匹配的可变形图像配准。利用所得的变形矢量场，将所有每日剂量分布D变形到计划千伏级计算机断层扫描上，并逐体素累积所得剂量。将累积剂量分布与计划剂量分布进行γ分析（2毫米，2.2 Gy的2%）比较。在第18次分割时执行了两种单干预ART策略，之前的数据表明该时间点适合进行单次重新计划干预：（1）在原始靶区和变形的危及器官（OARs）上重新计划（在肿瘤覆盖方面是一种“更安全”的方法），以及（2）在变形的靶区和变形的OARs上都重新计划。剂量分布显示计划剂量与实际交付剂量之间存在差异（三维γ 2毫米/2%通过率 = 85 ± 1%，p < 0.001）。逐体素剂量累积显示变形腮腺的平均剂量增加了3.0 Gy ± 3.3 Gy。采用ART时，当靶区和OARs都变形时，与未重新计划的实际交付剂量相比，变形腮腺的平均剂量降低了3.2 Gy ± 1.7 Gy。当仅OARs变形时，变形腮腺的平均剂量降低了2.0 Gy ± 1.4 Gy。解剖学变异导致腮腺剂量增加。在第18次MVCT上进行重新计划的有效单干预ART策略可降低腮腺剂量。对靶区和OARs都进行变形的策略导致腮腺剂量最低，但在形式上保持了计划靶区（PTV）的覆盖。然而，仅对OARs进行变形也能降低腮腺剂量，并且在PTV覆盖方面具有较少的不确定性。
