The Effects of the Amount of Bladder Filling on Normal Tissue Doses in 3-dimensional HDR Vaginal Cuff Brachy Therapy

Abstract

This study aimed to compare the dose-volume parameters of organs at risk (OAR) (bladder, rectum, sigmoid and bowel) for the bladder filling of 50cc versus 150cc in high-dose-rate (HDR) (3-D) vaginal cuff (VC) brachytherapy (BRT). METHODS The treatment data of eight hysterectomized patients with gynecological malignancy who received postoperative pelvic external radiotherapy (RT)+3-D HDR VC-BRT were analyzed. Recontouring was performed on CT images, and BRT plans were reformed. Proximal 1/3 vagina was treated in all patients using a cylinder. A total dose of 18 Gy (3x6Gy) was given (0.5 cm depth from the vaginal mucosa). OAR and clinical target volume (CTV) were recontoured in a 3-D manner. Afterwards, treatment planning was performed by a medical physicist using the BRT treatment planning system. Bladder V50%, D50% and D2cc, rectum D2cc, sigmoid D2cc, bowel D50% and D2cc were recorded from the dose-volume histograms obtained in the treatment planning system. Paired comparisons were made for the parameters above for the bladder filling of 50cc versus 150cc. Two different amounts of bladder filling were compared using the Wilcoxon Signed-Rank Test in the SPSS 15.0 statistics program. RESULTS Bladder D50% decreased (p=0.012) while bladder D2cc increased (p=0.025) in the case of 150cc bladder filling instead of 50cc. Rectum D2cc showed a statistical trend for increase (p=0.05); however, bowel D50% decreased (p=0.012) in 150cc bladder filling compared to 50cc. CONCLUSION The statistically significant decrease in bladder and especially bowel D50% parameters supports filling the bladder with 150cc instead of 50cc in 3-D VC-BRT.