Novel parameter predicting grade 2 rectal bleeding after iodine-125 prostate brachytherapy combined with external beam radiation therapy.

ABSTRACT

PURPOSE: To propose a novel parameter predicting rectal bleeding on the basis of generalized equivalent uniform doses (gEUD) after (125)I prostate brachytherapy combined with external beam radiation therapy and to assess the predictive value of this parameter. METHODS AND MATERIALS To account for differences among radiation treatment modalities and fractionation schedules, rectal dose-volume histograms (DVHs) of 369 patients with localized prostate cancer undergoing combined therapy retrieved from corresponding treatment planning systems were converted to equivalent dose-based DVHs. The gEUDs for the rectum were calculated from these converted DVHs. The total gEUD (gEUDsum) was determined by a summation of the brachytherapy and external-beam radiation therapy components. RESULTS: Thirty-eight patients (10.3%) developed grade 2+ rectal bleeding. The grade 2+ rectal bleeding rate increased as the gEUDsum increased 2.0% (2 of 102 patients) for <70 Gy, 10.3% (15 of 145 patients) for 70-80 Gy, 15.8% (12 of 76 patients) for 80-90 Gy, and 19.6% (9 of 46 patients) for >90 Gy (P=.002). Multivariate analysis identified age (P=.024) and gEUDsum (P=.000) as risk factors for grade 2+ rectal bleeding. CONCLUSIONS: Our results demonstrate gEUD to be a potential predictive factor for grade 2+ late rectal bleeding after combined therapy for prostate cancer.