Prostate Cancer Radiotherapy Dose Response: An Update of the Fox Chase Experience

Abstract

The effectiveness of increasing radiotherapy dose for men with prostate cancer was evaluated with reference to prognostic groups as defined by pretreatment serum prostate specific antigen (PSA), Gleason score, T stage and perineural invasion. There were 839 men treated between April 1989 and December 1997 with conformal radiotherapy alone. Cox multivariate analysis was used to establish important predictors of biochemical failure (BF) separately for patients with an initial pretreatment PSA (iPSA) of less than 10, 10 to 19.9, or 20 or greater ng/ml. Radiotherapy (RT) dose was evaluated as a continuous and categorical (dose groups of less than 72, 72 to 75.9 and 76 Gy or greater) variable. At a median 63-month followup multivariate analysis demonstrated that iPSA and radiotherapy (RP) dose were the most significant predictors of BF, followed by Gleason score and T stage. Perineural invasion was not an independent correlate of outcome. RT dose was significant in all iPSA groups (less than 10, 10 to 19.9 and 20 or greater ng/ml). Gleason score was significant when iPSA was less than 10 ng/ml. T stage was significant when iPSA was 20 ng/ml or greater and it was borderline when iPSA was 10 to 19.9 ng/ml (p = 0.08). Prognostic subgroups were derived from these results and tested for an effect of RT dose on univariate analysis. Radiation dose was not a correlate of BF in the most favorable (PSA less than 10 ng/ml and Gleason score 2 to 6) and the most unfavorable (PSA 20 ng/ml or greater and stage T3-T4) prognostic groups but it was otherwise an influential determinant of outcome. RT dose escalation to 76 Gy or greater improved patient outcome for all prognostic groups except those at the favorable and unfavorable extremes.