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

Abstract

OBJECTIVEThis 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) vaginalcuff (VC) brachytherapy (BRT).METHODSThe 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 patientsusing a cylinder. A total dose of 18 Gy (3x6Gy) was given (0.5 cm depth from the vaginal mucosa). OARand clinical target volume (CTV) were recontoured in a 3-D manner. Afterwards, treatment planningwas 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-volumehistograms 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 werecompared using the Wilcoxon Signed-Rank Test in the SPSS 15.0 statistics program.RESULTSBladder 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, bowelD50% decreased (p=0.012) in 150cc bladder filling compared to 50cc.CONCLUSIONThe statistically significant decrease in bladder and especially bowel D50% parameters supports fillingthe bladder with 150cc instead of 50cc in 3-D VC-BRT.