Phase II Feasibility Study of High-Dose Radiotherapy for Prostate Cancer Using Proton Boost Therapy: First Clinical Trial of Proton Beam Therapy for Prostate Cancer in Japan

OBJECTIVE: To assess the feasibility of high-dose radiotherapy for prostate cancer using proton boost therapy following photon radiotherapy. METHODS: The primary endpoint was acute grade 3 or greater genitourinary (GU) and gastrointestinal (GI) toxicities. The study included patients with clinical stage T1-3N0M0 prostate cancer. Radiotherapy consisted of 50 Gy/25 fx photon irradiation to the prostate and the bilateral seminal vesicles followed by proton boost of 26 Gy(E)/13 fx to the prostate alone. Hormonal therapy was allowed before and during the radiation therapy. RESULTS: Between January 2001 and January 2003, 30 patients were enrolled in this study. Acute grade 1/2 GU and GI toxicities were observed in 20/4 and 17/0 patients, respectively. With the median follow-up period of 30 months (range 20-45), late grade 1/2 GU and GI toxicities occurred in 2/3 and 8/3 patients, respectively. No grade 3 or greater acute or late toxicities were observed. All patients were alive, but six patients relapsed biochemically after 7-24 months. CONCLUSIONS: Proton boost therapy following photon radiotherapy for prostate cancer is feasible. To evaluate the efficacy and safety of proton beam therapy, a multi-institutional phase II trial is in progress in Japan.