Updated Results and Patterns of Failure in a Randomized Hypofractionation Trial for High-risk Prostate Cancer

Abstract

To report long-term results and patterns of failure after conventional and hypofractionated radiation therapy in high-risk prostate cancer. This randomized phase III trial compared conventional fractionation (80 Gy at 2 Gy per fraction in 8 weeks) vs hypofractionation (62 Gy at 3.1 Gy per fraction in 5 weeks) in combination with 9-month androgen deprivation therapy in 168 patients with high-risk prostate cancer. Freedom from biochemical failure (FFBF), freedom from local failure (FFLF), and freedom from distant failure (FFDF) were analyzed. In a median follow-up of 70 months, biochemical failure (BF) occurred in 35 of the 168 patients (21%) in the study. Among these 35 patients, local failure (LF) only was detected in 11 (31%), distant failure (DF) only in 16 (46%), and both LF and DF in 6 (17%). In 2 patients (6%) BF has not yet been clinically detected. The risk reduction by hypofractionation was significant in BF (10.3%) but not in LF and DF. We found that hypofractionation, with respect to conventional fractionation, determined only an insignificant increase in the actuarial FFBF but no difference in FFLF and FFDF, when considering the entire group of patients. However, an increase in the 5-year rates in all 3 endpoints-FFBF, FFLF, and FFDF-was observed in the subgroup of patients with a pretreatment prostate-specific antigen (iPSA) level of 20 ng/mL or less. On multivariate analysis, the type of fractionation, iPSA level, Gleason score of 4+3 or higher, and T stage of 2c or higher have been confirmed as independent prognostic factors for BF. High iPSA levels and Gleason score of 4+3 or higher were also significantly associated with an increased risk of DF, whereas T stage of 2c or higher was the only independent variable for LF. Our results confirm the isoeffectiveness of the 2 fractionation schedules used in this study, although a benefit in favor of hypofractionation cannot be excluded in the subgroup of patients with an iPSA level of 20 ng/mL or less. The α/β ratio might be more appropriately evaluated by FFLF than FFBF results, at least in high-risk disease.