Predicting genitourinary toxicity in three-dimensional conformal radiotherapy for localized prostate cancer: A dose-volume parameters analysis of the bladder

Purpose: In prostate cancer radiotherapy, the relationship between genitourinary (GU) toxicity and clinical-dosimetric parameters is debated. We report our analysis of the parameters associated with GU toxicity. Materials and Methods: Eighty-six consecutive patients treated with conformal radiotherapy for localized prostate cancer were retrospectively analyzed; the bladder was delineated both as 'whole bladder' (WB: Defined in its entirety as a solid organ) and 'inferior bladder' (IB: Corresponding to the distal part of the bladder). GU toxicity and dose-volume parameters were correlated using the point biserial correlation coefficient. The normal tissue complication probability (NTCP) cut-off volume model was fitted to toxicity data; univariate analysis between GU toxicity and clinical parameters was done. Results: Acute GU toxicity was correlated to doses higher than 80 Gy (P < 0.05) while late GU was correlated to doses higher than 77 Gy for WB and from 77.5 Gy for IB. The NTCP cut-off volume model identified for both WB and IB a bladder volume of 6 cc receiving a dose ≥77 Gy corresponding to a 50% probability of GU toxicity. At univariate analysis, acute GU toxicity was correlated with smoke (P < 0.001). Conclusion: Bladder maximal doses quantified as hotspots show a correlation to GU toxicity.