Eight years experience with neutron radiotherapy in the treatment of stages C and D prostate cancer: updated results of the RTOG 7704 randomized clinical trial.

The records of 91 patients enrolled between June 1977 and April 1983 in the Radiation Therapy Oncology Group (RTOG) randomized study investigating fast neutron radiation therapy in the treatment of locally advanced prostate cancer were reviewed. Patients with stages C and D1 adenocarcinoma were randomized to receive either combined fast neutron and photon irradiation (mixed-beam) or conventional photon irradiation alone. Survival (actuarial) at eight years for the mixed-beam cohort was 63% vs 13% for the patients receiving photons alone (P = .01). Corresponding "determinental" survival rates, adjusted by exclusion of intercurrent deaths, were 82% and 54%, respectively (P = .02). Freedom from locally recurrent prostate cancer was 77% for mixed-beam patients and 31% for patients receiving photons alone (P less than .01). Analyses of outcomes accounting for all major prognostic determinants confirm the greater efficacy of mixed beam treatment with P less than .05 for survival, determinental survival, and local control.