Purpose: To compare dose summation using a single plan (SP) approach for vaginal cuff brachytherapy (VBT) against dose summation after a rigid or deformable registration for each VBT fraction, in women with early stage endometrial cancer receiving postoperative VBT.
Methods and materials: A retrospective analysis of 19 patients who received VBT as the sole adjuvant treatment was undertaken. For the purposes of the study, every VBT fraction was re-segmented and re-planned under the same conditions. CT-planning images were registered, initially following a rigid method and then using deformable registration. The transformation vectors were reused to warp the dose files, followed by the dose summation. Three dose accumulation scenarios were studied: (1) an SP approach, (2) a rigid dose warping summation (RDWS), (3) a deformable dose warping summation (DDWS). Each scenario was analyzed for 3 and 5 fractions to evaluate the effect of fractionation. D0.1cc, D1cc, D2cc, D5cc, D5%, and Dmean values were compared for organs at risk, such as the rectum and bladder.
Results: No statistical significances were observed in rectal parameters between SP and RDWS or between SP and DDWS. Significant SP, RDWS and DDWS Dmean, D0.1cc, and D2cc metric differences for the 5 fractions bladder scenario were observed (p = 0.0242, 0.0196, and 0.0242, respectively).
Conclusions: A multi-image planning procedure for a VBT course leads to limited differences between different summation methods. SP is an effective and acceptable surrogate for absorbed doses in organs at risk.
Keywords: Cylinder; Deformable registration; Dose accumulation; Endometrium; Rigid registration.
Copyright © 2014 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.