Hypofractionated Versus Standard Fractionated Proton-beam Therapy for Low-risk Prostate Cancer: Interim Results of a Randomized Trial PCG GU 002

To identify differences in terms of quality of life, the American Urological Association Symptom Index (AUA), or adverse events (AEs) among patients with prostate cancer treated with either standard fractionation or hypofractionation proton-beam therapy. Patients were prospectively randomized to receive 38 Gy relative biological effectiveness (RBE) in 5 treatments (n=49) or 79.2 Gy RBE in 44 treatments (n=33). All patients had low-risk prostate cancer and were treated with proton therapy using fiducial markers and daily image guidance. Median follow-up for both groups was 18 months; 33 patients had follow-up of 2 years or longer. Baseline median (range) AUA was 4.7 (0 to 13) for the 38 Gy RBE arm and 4.8 (0 to 17) for the 79.2 Gy RBE arm. We observed no difference between the groups regarding the Expanded Prostate Index Composite urinary, bowel, or sexual function scores at 3, 6, 12, 18, or 24 months after treatment. The only significant difference was the AUA score at 12 months (8 for the 38 Gy RBE arm vs. 5 for the 79.2 Gy RBE arm; P=0.04); AUA scores otherwise were similar between groups. No grade 3 or higher AEs occurred in either arm. Patients treated with proton therapy in this randomized trial tolerated treatment well, with excellent quality-of-life scores, persistent low AUA, and no grade 3 or higher AEs on either arm. We showed no apparent clinical difference in outcomes with hypofractionated proton-beam therapy compared with standard fractionation on the basis of this interim analysis.