Quantitative Analyses of Variability of Proximal Vaginal Wall Thickness in Vaginal Cuff Brachytherapy for Gynecologic Tumor– Multichannel Balloon Vs. Single-Channel Cylinder

Abstract

To evaluate the thickness of proximal vaginal wall during vaginal cuff brachytherapy (VCB) and compare results between cases treated using single-channel cylinder (SCC) versus multichannel balloon (MCB). A total of 82 consecutive cases receiving high-dose-rate VCB including 41 by SCC and 41 by MCB were reviewed. The VCB CT images were used to measure the vaginal wall thickness. Multiple points along the proximal vaginal canal were measured including the apex position on the top of vagina, the anterior, posterior, left and right lateral positions at planes 0.5, 1, 2 and 3-cm from the top of vagina. As shown in Table 1, the thickness of proximal vaginal wall varies significantly. The mean thickness at the apex was 0.51 cm and 0.50 cm for SCC and MCB respectively. The vaginal wall is significant thicker at both left and right lateral positions compared to anterior and posterior positions at all measurement planes for both SCC and MCB. In addition, the mean vaginal wall thickness exceed 0.5 cm at left and right lateral position for all the measurement planes using SCC indicating potential underdose at lateral positions if the prescription point is placed at the 0.5 cm depth from the vaginal mucosa. In contrast, for MCB, the mean thickness of vaginal wall at lateral positions were smaller than 0.5 cm in all planes except measurement done at 0.5cm distance from the apex, where left and right lateral positions had a mean depth of 0.58 and 0.53 cm respectively and the left lateral 1cm distance from the apex where the left lateral position had a mean depth of 0.52 cm, indicating the importance to optimize VCB treatment plans by adding/reducing weighting on the peripheral channels. The mean vaginal wall thickness at anterior and posterior positions for SCC and MCB were all less than 0.5 cm in all planes indicating advantages of using MCB to optimize plan to reduce damage to the rectum. There is high variability in the thickness of proximal vaginal wall and compared to SCC, MCB can stretch and thin the vaginal wall, especially the lateral positions further and provide dosimetric advantages. In addition, MCB offers multiple dwell positions to optimize the dose distribution to accommodate different vaginal wall thickness at various locations.Abstract 2822; Table 1Vaginal wall thickness (cm, mean ±SD) at planes 0.5, 1, 2 and 3-cm from the top of vagina (all statistically significant except *)cmAnteriorPosteriorLeft lateralRight lateralMCBSCCMCBSCCMCBSCCMCBSCC0.50.42±0.140.50±0.160.26±0.110.36±0.120.58±0.30*0.52±0.19*0.53±0.21*0.58±0.23*10.35±0.090.48±0.180.22±0.090.34±0.130.52±0.17*0.58±0.16*0.44±0.110.58±0.2520.36±0.090.45±0.120.25±0.080.32±0.070.41±0.110.63±0.210.40±0.090.56±0.1830.35±0.070.49±0.090.25±0.070.33±0.100.39±0.100.61±0.140.37±0.090.56±0.19 Open table in a new tab