DVH parameters and gastrointestinal/genitourinary toxicities in moderate hypofractionated salvage radiotherapy after radical prostatectomy.

This study aimed to evaluate the relationships between dose-volume histogram (DVH) parameters and gastrointestinal (GI) and genitourinary toxicity in patients who underwent moderate hypofractionated salvage radiotherapy after radical prostatectomy. We retrospectively reviewed patients who received moderate hypofractionated salvage radiotherapy (65 Gy in 26 fractions, four fractions per week) between 2013 and 2022. DVH parameters of the rectum, anal canal, whole bladder, bladder neck, and bladder trigone were assessed in relation to toxicity. Optimal cut-off values were determined using receiver operating characteristic curve analysis. Ninety-two patients were included, with a median follow-up of 5.2 years. Grade ≥ 2 acute rectal bleeding, acute anal pain, late rectal bleeding, and grade ≥ 1 late hematuria occurred in 13%, 24%, 14%, and 33% of patients, respectively. Acute GI toxicity was associated with low-to-moderate doses to the anal canal, whereas late rectal bleeding was associated with moderate-to-high doses to the rectum. In multivariable analysis, anal canal V20Gy and hypertension were independent predictors of acute rectal bleeding, and rectum V60Gy and acute rectal bleeding were independently associated with late rectal bleeding. These findings may contribute to establishing DVH thresholds that facilitate dose optimization in moderate hypofractionated salvage radiotherapy after radical prostatectomy.