Single or multi-channel vaginal cuff high-dose-rate brachytherapy: Is replanning necessary prior to each fraction?

Purpose: Adjuvant high-dose-rate vaginal brachytherapy (VB) is commonly used in endometrial cancer. We evaluated the dosimetric and cost differences of using either a single plan or replan prior to each fraction for single- and multi-channel VB. Methods and Materials: We evaluated 84 fractions from 25 patients at our institution (16 singlechannel patients each 3 fractions; 9 multi-channel patients each 4 fractions). All fractions were preceded by a computed tomographic (CT) simulation scan, after which a unique treatment plan was generated, dose points per International Commission on Radiation Units and Measurements (ICRU) 38. We calculated the dose to critical organs based on a decay-and-treat method utilizing the original catheter dwell-times for the initial fraction, and also the interfractional motion of the critical organ points between the initial and the subsequent CT scans. Results: The absolute mean dose difference was 14 cGy for bladder and 15 cGy for rectum between the replan and decay methods for single-channel, and 14 cGy for both organ points for the multi-channel cylinder. The bladder and rectum doses were not found to be significantly different between the replan and decay methods for either single-channel (bladder, P = .08; rectum, P = .19) or multi-channel cylinders (bladder, P = .85; rectum, P = .10). The mean interfractional displacement of the organ points between the initial and subsequent CT scans was 1.10 cm for the bladder and 0.67 cm for the rectum for single-channel, and 0.87 cm and 0.51 cm for multi-channel cylinders. The maximum interfractional motion was seen in the transverse plane for both organ points for both types of cylinders. At our institution, the decay method was 19% and 22% more cost-effective for single-channel and multi-channel cylinders, respectively. Conclusions: Our data show no dosimetric advantage, but higher costs, associated with replanning prior to each fraction for both single- and multi-channel VB. Fractional replanning should not be utilized on a routine basis.