Relationships between bladder dose-volume/surface histograms and acute urinary toxicity after radiotherapy for prostate cancer

Background and purpose DUE01 is an observational study aimed at developing predictive models of genito-urinary toxicity of patients treated for prostate cancer with conventional (1.8-2 Gy/fr, CONV) or moderate hypo-fractionation (2.35-2.7 Gy/fr, HYPO). The current analysis focused on the relationship between bladder DVH/DSH and the risk of International Prostate Symptoms Score (IPSS) ≥ 15/20 at the end of radiotherapy. Materials and methods Planning and relevant clinical parameters were prospectively collected, including DVH/DSH, LQ-corrected (DVHc/DSHc) and weekly (DVHw/DSHw) histograms. Best parameters were selected by the differences between patients with/without IPSS ≥ 15/20 at the end of radiotherapy. Logistic uni- and backward multi-variable (MVA) analyses were performed. Results Data of 247 patients were available (CONV: 116, HYPO: 131). Absolute DVHw/DSHw and DVHc/DSHc predicted the risk of IPSS ≥ 15 at the end of radiotherapy (n = 77/247); an MVA model including baseline IPSS, anti-hypertensive, T stage, the absolute surface receiving ≥8.5 Gy/week and ≥12.5 Gy/week was developed (AUC = 0.78, 95% CI: 0.72-0.83). Similar AUC values were found if replacing DSHw with DVHw/DVHc/DSHc parameters. The impact of dose-volume/surface parameters remained when excluding patients with baseline IPSS ≥ 15 and in HYPO. IPSS ≥ 20 at the end of radiotherapy (n = 27/247) was mainly correlated to baseline IPSS and T stage. Conclusions Although the baseline IPSS was the main predictor, constraining v8.5w < 56 cc and v12.5w < 5 cc may significantly reduce acute GU toxicity.