Dosimetric comparison of multichannel with one single-channel vaginal cylinder for vaginal cancer treatments with high-dose-rate brachytherapy

Abstract

To compare the three-dimensional (3D) image (CT/MR)-based planning with a multichannel vaginal cylinder (MVC) to a single-channel vaginal cylinder (SVC) for the treatment of vaginal cancer. A total of 20 consecutive patients were treated with 3D CT/MR image-based high-dose-rate (HDR) brachytherapy using an MVC. All patients received external beam radiation therapy before HDR brachytherapy. A brachytherapy dose of 20-25Gy of more than five fractions was delivered to clinical target volume (CTV). Retrospectively, treatment plans for all patients were generated using the central channel only to mimic an SVC applicator. The SVC plans were optimized to match CTV coverage with MVC plans. Dose homogeneity index as well as bladder, rectum, sigmoid, and urethral doses were compared. The mean D90 for CTV was 74.2Gy (range: 48.8-84.1Gy). The mean (±standard deviation) of dose homogeneity index for MVC vs. SVC was 0.49 (±0.19) and 0.52 (±0.23), respectively (p=0.09). Mean bladder 0.1, 1, and 2cc doses for MVC vs. SVC were 69 vs. 71.2Gy (p=0.35), 61.4 vs. 63.8Gy (p=0.1), and 59.5 vs. 60.9Gy (p=0.31), respectively. Similarly, mean rectum 0.1, 1, and 2cc doses for MVC vs. SVC were 67.2 vs. 75.4Gy (p=0.005), 60.0 vs. 65.6Gy (p=0.008), and 57.3 vs. 62.0Gy (p=0.015), respectively, and mean sigmoid doses were 56.3 vs. 60.5Gy (p=0.10), 50.9 vs. 53.1Gy (p=0.09), and 49.1 vs. 50.7Gy (p=0.10), respectively. The 3D CT-/MR-based plan with MVC may provide better dose distribution in the management of certain clinical situations of vaginal cancer requiring intracavitary brachytherapy, especially in minimizing potential late rectal complications.