Abstract
INTRODUCTION AND HYPOTHESIS: Female survivors of endometrial and rectal cancers have increased risk of urinary incontinence. Survivors with prior radiation therapy are counseled against mesh incontinence surgery. We hypothesize that urethral radiation dose varies based on modality which may influence surgical risks. We aimed to demonstrate urethral radiation dose differences between vaginal brachytherapy (VBT) and external beam radiation therapy (EBRT). METHODS: This is a retrospective cohort study of women exposed to VBT for endometrial cancer and EBRT for rectal cancer. The urethra was contoured on CT imaging to calculate radiation doses in centigray (cGy). The primary outcome was the percent of treatment radiation dose estimated to be received by the urethra based on the volume dose to 0.2 cc of urethra. Secondary outcomes were point doses to the bladder neck, mid-urethra, and total mean urethral dose. Descriptive statistics described demographic characteristics. Bivariate analyses compared urethral radiation dose based on radiation modality. RESULTS: Between 2014-2017, 32 women treated were included: 18 with VBT and 14 with EBRT. Mean ± SD urethral volume doses were lower in VBT (1266 cGy ± 533, 42.2% of prescribed treatment dose) compared to EBRT (5051 cGy ± 192, 100.2% of prescribed treatment dose), p < 0.0001. VBT also had significantly lower mean total urethral dose and point doses to bladder neck and mid- urethra compared to EBRT (p < 0.0001). CONCLUSIONS: The female urethra is exposed to significantly less radiation in VBT compared to EBRT. These data highlight that modality of pelvic radiation should be considered in treatment counseling on urinary incontinence in women.