Radiotherapy Research Today is a free monthly online journal that collates and summarizes the latest research about Radiotherapy, including details on cancer treatment, side effects.

Increasing external beam dose for T1-T2 prostate cancer: effect on risk groups.

Thames HD, Kuban DA, DeSilvio ML, Levy LB, Horwitz EM, Kupelian PA, Martinez AA, Michalski JM, Pisansky TM, Sandler HM, Shipley WU, Zelefsky MJ, Zietman AL

Department of Biostatistics and Applied Mathematics, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, and Department of Radiation Oncology, William Beaumont Hospital, Deroit, MI, USA. hdt@odin.mdacc.tmc.edu

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>or=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 were common, and it is inconsistent with risk groups for patients treated to doses>70 Gy. Risk-group classifications must be continuously re-examined whenever the trend is toward increasing total dose.

Published 26 June 2006 in Int J Radiat Oncol Biol Phys, 65(4): 975-81.
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