Increasing external beam dose for T1–T2 prostate cancer: Effect on risk groups

Purpose: The aim of this study was to investigate effect of increasing dose on risk groups for clinical failure (CF: local failure or distant failure or hormone ablation or PSA ≥25 ng/ml) in patients with T1–T2 prostate cancer treated with external beam radiotherapy. Methods and Materials: Patients ( n = 4,537) were partitioned into nonoverlapping dose ranges, each narrow enough that dose was not a predictor of CF, and risk groups for CF were determined using recursive partitioning analysis (RPA). The same technique was applied to the highest of these dose ranges (70–76 Gy, 1,136 patients) to compare risk groups for CF in this dose range with the conventional risk-group classification. Results: Cutpoints defining low-risk groups in each dose range shifted to higher initial PSA levels and Gleason scores with increasing dose. Risk groups for CF in the dose range 70–76 Gy were not consistent with conventional risk groups. Conclusions: The conventional classification of risk groups was derived in the early PSA era, when total doses 70 Gy. Risk-group classifications must be continuously re-examined whenever the trend is toward increasing total dose.