Significant correlation between rectal DVH and late bleeding in patients treated after radical prostatectomy with conformal or conventional radiotherapy (66.6–70.2 Gy)

Abstract

Purpose: Investigating the correlation between dosimetric/clinical parameters and late rectal bleeding in patients treated with adjuvant or salvage radiotherapy after radical prostatectomy. Methods and Materials: Data of 154 consecutive patients, including three-dimensional treatment planning and dose-volume histograms (DVHs) of the rectum (including filling), were retrospectively analyzed. Twenty-six of 154 patients presenting a (full) rectal volume >100 cc were excluded from the analysis. All patients considered for the analysis ( n = 128) were treated at a nominal dose equal to 66.6–70.2 Gy (ICRU dose 68–72.5 Gy; median 70 Gy) with conformal ( n = 76) or conventional ( n = 52) four-field technique (1.8 Gy/fr). Clinical parameters such as diabetes mellitus, acute rectal bleeding, hypertension, age, and hormonal therapy were considered. Late rectal bleeding was scored using a modified Radiation Therapy Oncology Group scale, and patients experiencing ≥Grade 2 were considered bleeders. Median follow-up was 36 months (range 12–72). Mean and median rectal dose were considered, together with rectal volume and the % fraction of rectum receiving more than 50, 55, 60, and 65 Gy (V50, V55, V60, V65, respectively). Median and quartile values of all parameters were taken as cutoff for statistical analysis. Univariate (log-rank) and multivariate (Cox hazard model) analyses were performed. Results: Fourteen of 128 patients experienced ≥Grade 2 late bleeding (3-year actuarial incidence 10.5%). A significant correlation between a number of cutoff values and late rectal bleeding was found. In particular, a mean dose ≥54 Gy, V50 ≥63%, V55 ≥57%, and V60 ≥50% was highly predictive of late bleeding ( p ≤ 0.01). A rectal volume <60 cc and type of treatment (conventional vs. conformal) were also significantly predictive of late bleeding ( p = 0.05). Concerning clinical variables, acute bleeding ( p < 0.001) was significantly related to late bleeding, and a trend was found for hypertension ( p = 0.11). After patients were grouped into those with V50 ≥63% and those with V50 <63% (DVH grouping), data were fitted with a Cox regression hazard model using DVH grouping, rectal volume, and the main clinical parameters as independent variables. Results of the analysis showed that DVH grouping (relative risk 3.3; p = 0.04) and acute bleeding (relative risk 7.1; p = 0.001) are independently predictive of late bleeding. Conclusions: DVHs of the rectum are significantly correlated with late bleeding for patients irradiated at 66.6–70.2 Gy after radical prostatectomy.