Online adaptive radiotherapy (ART) allows adaptation of the dose distribution to the anatomy captured by with pre-adaptation imaging. ART is time-consuming, and thus intra-fractional deformations can occur. This prospective registry study analyzed the effects of intra-fraction deformations of clinical target volume (CTV) on the equivalent uniform dose (EUDCTV) of focal bladder cancer radiotherapy. Using margins of 5–10 mm around CTV on pre-adaptation imaging, intra-fraction CTV-deformations found in a second imaging study reduced the 10th percentile of EUDCTVvalues per fraction from 101.1% to 63.2% of the prescribed dose. Dose accumulation across fractions of a series was determined with deformable-image registration and worst-case dose accumulation that maximizes the correlation of cold spots. A strong fractionation effect was demonstrated—the EUDCTVwas above 95% and 92.5% as determined by the two abovementioned accumulation methods, respectively, for all series of dose fractions. A comparison of both methods showed that the fractionation effect caused the EUDCTVof a series to be insensitive to EUDCTV-declines per dose fraction, and this could be explained by the small size and spatial variations of cold spots. Therefore, ART for each dose fraction is unnecessary, and selective ART for fractions with large inter-fractional deformations alone is sufficient for maintaining a high EUDCTVfor a radiotherapy series.
在线自适应放疗（ART）允许根据预适应成像所捕获的解剖结构调整剂量分布。ART过程耗时较长，因此可能发生分次内形变。这项前瞻性注册研究分析了分次内临床靶区（CTV）形变对膀胱癌局部放疗等效均匀剂量（EUDCTV）的影响。在预适应成像中对CTV设置5-10毫米边界时，二次成像研究中发现的分次内CTV形变使每次分次的EUDCTV值第10百分位数从处方剂量的101.1%降至63.2%。通过可变形图像配准和最大化冷点相关性的最差情况剂量累积方法，确定了整个放疗序列中各分次的剂量累积效应。研究显示出强烈的分次效应——采用上述两种累积方法计算，所有放疗序列的EUDCTV分别保持在95%和92.5%以上。两种方法的比较表明，分次效应使得整个放疗序列的EUDCTV对单次分次的EUDCTV下降不敏感，这可通过冷点范围较小且空间位置变化来解释。因此，每次分次均进行ART并无必要，仅对存在较大分次间形变的分次实施选择性ART，即可维持整个放疗序列的高EUDCTV水平。
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