Pöttgen Christoph, Hoffmann Christian, Gauler Thomas, Guberina Maja, Guberina Nika, Ringbaek Toke, Santiago Garcia Alina, Krafft Ulrich, Hadaschik Boris, Khouya Aymane, Stuschke Martin
Department of Radiotherapy, University of Duisburg-Essen, Hufelandstr. 55, 45147 Essen, Germany.
Department of Urology, University of Duisburg-Essen, 45147 Essen, Germany.
Cancers (Basel). 2023 Oct 11;15(20):4933. doi: 10.3390/cancers15204933.
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 (EUD) 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 EUD values 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 EUD was 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 EUD of a series to be insensitive to EUD-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 EUD for a radiotherapy series.
在线自适应放疗（ART）可根据预适应成像所捕获的解剖结构调整剂量分布。ART耗时较长，因此可能会发生分次内形变。这项前瞻性注册研究分析了临床靶区（CTV）的分次内形变对局限性膀胱癌放疗等效均匀剂量（EUD）的影响。在预适应成像中，使用CTV周围5-10毫米的边界，在第二次成像研究中发现的分次内CTV形变使每分次EUD值的第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使冷区相关性最大化的最坏情况剂量累积来确定一系列分次的剂量累积。结果显示出明显的分次效应——对于所有剂量分次系列，通过上述两种累积方法确定的EUD分别高于95%和92.5%。两种方法的比较表明，分次效应使一系列的EUD对每剂量分次的EUD下降不敏感，这可以通过冷区的小尺寸和空间变化来解释。因此，每次剂量分次进行ART并无必要，仅对分次间形变较大的分次进行选择性ART就足以在放疗系列中维持较高的EUD。
