Correlation between dosimetrical data and rectal bleeding in radiotherapy of prostate cancer: a retrospective analysis

The purpose of current study is to search for possible correlation between dosimetry-clinical-technical parameters and late grade II/III rectum bleeding through a retrospective analysis of 175 patients (conformal: 115; non-conformal: 60) treated in the two Institutes for prostate carcinoma with curative or adjuvant intent (ICRU dose ranging from 60 to 76 Gy) in the years 1994-1998. The dose -volume-histograms (DVH) and dose statistics were collected together with a number of clinical and technical/dosimetry data. Mean, median and maximum dose and the fraction of rectum receiving more than 50, 55, 60, 65, 70 and 75 Gy were considered (V50,55,60,65,70,75). Rectal toxicity was scored through the RTOG/EORTC scale [1]: minimum follow-up was 15 months. 23/ 175 patients (13.1%) experienced grade II-III bleeding (grade III: 1/175). Posterior wall irradiation (more than 2 cm, 33% vs. 8.5%) and type of technique (conformal or not, 6% vs. 26%) were significantly correlated with the risk of grade II/III bleeding (p < 0.001. chi (2) test). When considering the greater than or equal to 70 Gy patients (n = 126) a number of constraints resulted to be significant (chi (2) test): mean dose ( greater than or equal to 57 Gy, p = 0.03); median dose ( greater than or equal to 64 Gy, p = 0.025); V70 ( greater than or equal to 35%, p = 0.025); V65 ( greater than or equal to 48%, p = 0.03) V50 ( greater than or equal to 69%, p = 0.04).