PHOTON VERSUS FAST-NEUTRON EXTERNAL-BEAM RADIOTHERAPY IN THE TREATMENT OF LOCALLY ADVANCED PROSTATE-CANCER - RESULTS OF A RANDOMIZED PROSPECTIVE TRIAL

Purpose: To evaluate the effectiveness of fast neutron radiation thera py in treatment of locally advanced carcinomas of the prostate. Method s and Materials: From April 1986 to October 1990, 178 patients were en tered on a prospective, multi-institutional randomized study of the NC I-sponsored Neutron Therapy Collaborative Working Group. This trial co mpared external beam photon irradiation (7000-7020 cGy) with external beam neutron irradiation (2040 ncGy) for patients with high-grade T-2 or T-3-4 N-0-1, M(0) adenocarcinomas of the prostate. Eighty-nine pati ents were randomized to each treatment. Six patients were subsequently judged to be ineligible, leaving 85 photon and 87 neutron randomized patients eligible for analysis. Results: With a follow-up time ranging from 40 to 86 months (68 months median follow-up) the 5-year actuaria l clinical local-regional failure rate for patients treated with neutr ons was 11%, vs. 32% for photons (p < 0.01). Incorporating the results of routine posttreatment prostate biopsies, the resulting ''histologi cal'' local-regional tumor failure rates were 13% for neutrons vs. 32% for photons (p = 0.01). To date, actuarial survival and cause-specifi c survival rates are statistically indistinguishable for the two patie nt cohorts, with 32% of the neutron-treated patient deaths and 41% of the photon-treated patient deaths caused by prostate cancer (p = n.s.) . Prostate specific antigen (PSA) values were elevated in 17% of neutr on-treated patients and 45% of photon-treated patients at 5 years (p < 0.001). Severe late complications of treatment were higher for the ne utron-treated patients (11% vs. 3%), and were inversely correlated wit h the degree of neutron beam shaping available at the participating in stitutions. Neutron treatment delivery utilizing a fully rotational ga ntry and multileaf collimator did not result in an increase in severe late effects when compared to photon treatment. Conclusion: High energ y fast neutron radiotherapy is safe and effective when adequate beam d elivery systems and collimation are available, and it is significantly superior to external beam photon radiotherapy in the local-regional t reatment of large prostate tumors.