Davidson Melanie T M, Yuen Jasper, D'Souza David P, Batchelar Deidre L
Department of Clinical Physics and Engineering, The London Regional Cancer Program, London, Ontario, Canada.
Brachytherapy. 2008 Jan-Mar;7(1):37-42. doi: 10.1016/j.brachy.2007.12.003.
Intracavitary high-dose-rate (HDR) brachytherapy (BT) for cervical cancer involves multiple applicator insertions. Our study addresses whether customized three-dimensional plans generated for the first insertion (using computed tomography [CT] planning) can be applied to subsequent insertions without significant changes in dose distributions if identical applicators are used.
Twenty-seven patients were treated with external-beam radiotherapy, platinum-based chemotherapy, and HDR BT. Either tandem and ovoids (TO, n=12) or tandem and ring (TR, n=15) applicators were used, based on clinical indications. Postimplant CT scans were acquired and custom plans generated for each insertion. Dose parameters for organs at risk (OARs) from the second insertion were retrospectively compared to those that would have been delivered using the initial plan.
Overall, we observed a significant increase (p<0.038) in dose to International Commission on Radiation Units and Measurement points and 2cm(3) volumes of bladder and rectum when a single plan was used. The sigmoid and small bowel exhibited a more variable increase in dose. Applicator-specific results revealed a significant increase (p<0.030) to dose points and volumes for the rectum and bladder for TR applicators. Conversely, dose values from the more flexible TO did not show any significant trend, exhibiting large interpatient variations.
A duplication of planned dwell times and positions from one insertion to the next does not duplicate dose distributions in HDR cervix applications. A single plan used for an entire course of BT can result in significant increases to OAR doses for TR and unpredictable OAR doses for TO applicators. Treatment plans should be tailored for each insertion to reflect current applicator and anatomical geometry.
宫颈癌腔内高剂量率（HDR）近距离放射治疗（BT）涉及多次施源器插入。我们的研究探讨了为首次插入生成的定制三维计划（使用计算机断层扫描[CT]规划），如果使用相同的施源器，是否可以应用于后续插入而剂量分布无显著变化。
27例患者接受了外照射放疗、铂类化疗和HDR BT。根据临床指征，使用了串联卵形施源器（TO，n = 12）或串联环形施源器（TR，n = 15）。植入后进行CT扫描，并为每次插入生成定制计划。回顾性比较第二次插入时危及器官（OARs）的剂量参数与使用初始计划时的剂量参数。
总体而言，当使用单一计划时，我们观察到国际辐射单位与测量委员会点以及膀胱和直肠2cm³体积的剂量显著增加（p < 0.038）。乙状结肠和小肠的剂量增加更具变异性。特定施源器的结果显示，TR施源器的直肠和膀胱剂量点及体积显著增加（p < 0.030）。相反，更灵活的TO施源器的剂量值未显示任何显著趋势，患者间差异较大。
从一次插入到下一次插入重复计划的驻留时间和位置，在HDR宫颈癌应用中不会重复剂量分布。用于整个BT疗程的单一计划可能导致TR施源器的OAR剂量显著增加，而TO施源器的OAR剂量不可预测。治疗计划应针对每次插入进行定制，以反映当前的施源器和解剖结构。
