Acute toxicity of image-guided hypofractionated proton therapy for localized prostate cancer.

BACKGROUND: Hypofractionated proton therapy (HFPT) is expected to become an effective treatment approach for localized prostate cancer (PCa). The purpose of this study was to evaluate differences in acute toxicity among patients with localized PCa treated with either conventional fractionated proton therapy (CFPT) or HFPT.

METHODS: A total of 526 eligible patients treated with proton therapy between February 2013 and May 2016 in three phase II trials were analyzed. We prescribed 74 gray relative biological effectiveness equivalents [Gy (RBE)]/37 fractions for low-risk patients and 78 Gy (RBE)/39 fractions for intermediate- and high-risk patients in the CFPT group (n = 254) and 60 Gy (RBE)/20 fractions for low-risk and 63 Gy (RBE)/21 fractions for intermediate- and high-risk patients in the HFPT group (n = 272). Patients were evaluated for acute toxicity with the Common Terminology Criteria for Adverse Events, version 4.0, and urinary quality-of-life change using the International Prostate Symptom Score (IPSS).

RESULTS: No grade ≥3 acute toxicity was observed in either group. Among acute genitourinary toxicities, grade 2 rates were 15% (n = 38) in CFPT and 5.9% (n = 16) in HFPT (P ≤ 0.001). The median baseline IPSSs of the CFPT and HFPT groups were 7 (0-29) and 6 (0-31), respectively (P = 0.70). One-month post-treatment scores were 9 (0-32) and 11 (0-32), respectively (P = 0.036), and 6-month post-treatment scores were 7 (0-30) and 7 (0-33), respectively (P = 0.88). There were no significant differences in acute gastrointestinal toxicity between the two groups.

CONCLUSION: Our results demonstrated the safety of HFPT for localized PCa patients in terms of acute toxicity.