Association between acute histopathological changes of rectal walls and late radiation proctitis following radiotherapy for prostate cancer.

PURPOSE: The impact of acute histopathological changes (HC) of the rectum on development of late clinical proctitis (LCP) after external radiotherapy (RT) for prostate cancer is poorly explored and was the primary end point of this prospective study. METHODS: In 70 patients, 15 HC of early rectal biopsies after RT were identified, whereby RT was conventional 2D RT in 41 cases and conformational 3D RT in 29. Associations of HC in anterior and posterior rectal walls (ARW, PRW) with LCP, acute endoscopic (AEP) and acute clinical proctitis (ACP) were statistically evaluated considering as explicative variables the patient general characteristics and the HC. RESULTS: The mean patients' follow-up was 123.5 months (24-209). The median prostatic dose was 72 Gy (2 Gy/fraction). For the 41 and 29 patients the ARW and PRW doses were 64 and 49 Gy vs. 63 and 50 Gy, respectively. The incidence of LCP ≥ grade 2 at 10 years was 12.9%. The univariate (p = 0.02) and Kaplan-Meyer methods (p = 0.007) showed that the gland (or crypts) loss in the ARW was significantly associated with LCP. AEP and ACP occurred in 14.3 and 55.7% of cases. At multivariate level AEP significantly correlated with hemorrhoids (p = 0.014) and neutrophilia in ARW (p = 0.042). CONCLUSIONS: Early after RT, substantial gland loss in ARW is predictive of LCP. To reduce this complication with conventional fractionation, we suggest keeping the mean dose to ARW ≤48-52 Gy.