Interfraction anatomic deformations decrease the precision of radiotherapy, which can be improved by online adaptive radiation therapy (oART). However, oART takes time, allowing intrafractional deformations. In this study on focal radiotherapy for bladder cancer, we analyzed the time effect of oART on the equivalent uniform dose in the CTV (EUDCTV) per fraction and for the accumulated dose distribution over a treatment series as measure of effectiveness. A time-dependent digital CTV model was built from deformable image registration (DIR) between pre- and post-adaptation imaging. The model was highly dose fraction-specific. Planning target volume (PTV) margins were varied by shrinking the clinical PTV to obtain the margin-specific CTV. The EUDCTVper fraction decreased by—4.4 ± 0.9% of prescribed dose per min in treatment series with a steeper than average time dependency of EUDCTV. The EUDCTVfor DIR-based accumulated dose distributions over a treatment series was significantly dependent on adaptation time and PTV margin (p< 0.0001, Chi2 test for each variable). Increasing adaptation times larger than 10 min by five minutes requires a 1.9 ± 0.24 mm additional margin to maintain EUDCTVfor a treatment series. Adaptation time is an important determinant of the precision of oART for one half of the bladder cancer patients, and it should be aimed at to be minimized.
分次间解剖形变会降低放射治疗的精确性，在线自适应放射治疗（oART）可改善此问题。然而oART需要时间，这可能导致分次内形变。在本项针对膀胱癌局部放疗的研究中，我们分析了oART时间效应对单次分次CTV等效均匀剂量（EUDCTV）及整个治疗周期累积剂量分布的影响，以此评估治疗效果。通过自适应前后影像的形变配准（DIR），建立了时间依赖性数字化CTV模型。该模型具有高度剂量分次特异性。通过缩小临床计划靶区（PTV）边界获得不同边界宽度的CTV。在治疗周期中，EUDCTV单次分次剂量值以每分钟4.4±0.9%处方剂量的速率下降，其时间依赖性较平均水平更为显著。基于DIR的整个治疗周期累积剂量分布的EUDCTV显著依赖于自适应时间和PTV边界宽度（p<0.0001，各变量卡方检验）。当自适应时间超过10分钟后，每增加5分钟需要额外增加1.9±0.24 mm的边界宽度以维持治疗周期的EUDCTV。对于半数膀胱癌患者，自适应时间是影响oART精确性的重要决定因素，应致力于将其最小化。
肿瘤(癌症)患者之家