Dosimetric advantages of using multichannel balloons compared to single-channel cylinders for high-dose-rate vaginal cuff brachytherapy

PURPOSE: To evaluate the dosimetric advantages of using multichannel balloons (MCBs) vs. single-channel cylinders (SCCs) for high-dose-rate vaginal cuff brachytherapy. METHODS AND MATERIALS: A total of 91 consecutive high-dose-rate vaginal cuff brachytherapy including 45 MCB and 46 SCC treatments were reviewed. The clinical target volume (CTV) was defined as a 0.5-cm uniform expansion of the applicator surface from vaginal apex for 3 cm. For dosimetric comparison, we normalized prescription dose per fraction to 700 cGy and optimized each plan to cover at least 90% of CTV. CTV-1 cm, the true vaginal cuff volume, was defined as proximal 1 cm of CTV from vaginal apex. Four quality indices including conformity index (CI), dose homogeneity index, dose nonuniformity index, and overdose index were compared. RESULTS: The CTV and CTV-1 cm were significantly larger for MCB cases compared to SCC cases. Evaluating CTV coverage, the mean dose homogeneity index and dose nonuniformity index were superior for MCB than SCC. No differences were noted regarding CI and overdose index between MCB and SCC cases. However, focusing on CTV-1 cm, the difference of CI became significant in favor of MCB cases. In addition, the mean point dose at 0.5-cm depth from the apex was significantly lower in SCC cases compared to cases by MCB treatment, indicating inadequate vaginal apex coverage by SCC treatment. CONCLUSIONS: Compared to SCC, MCB treats a larger volume and offers a more conformal and homogeneous target coverage. In addition, a lower dose at the vaginal apex due to SCCs source anisotropy can be minimized. (C) 2016 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.