Four-year outcomes from a prospective phase II clinical trial of moderately hypofractionated proton therapy for localized prostate cancer.

Abstract

BACKGROUND\nModerately hypofractionated radiation therapy represents an effective treatment for localized prostate cancer (PC). While large randomized trials have shown the efficacy of photon-based hypofractionated therapy, hypofractionated proton therapy (HFPT) has not been extensively studied. This study was performed to determine the clinical and patient-reported outcomes for patients with PC treated with HFPT.\n\n\nMETHODS\nBetween 2010 and 2017, 184 men were enrolled on a trial of 70Gy in 28 fractions of HFPT for low to intermediate-risk PC. Acute and late toxicity was evaluated using CTCAEv4.0. Patient reported outcomes were measured by International Prostate Symptom Score (IPSS), International Index of Erectile Function (IIEF-5) Questionnaire, and Expanded Prostate Cancer Index Composite (EPIC) scores.\n\n\nRESULTS\nMedian follow-up was 49.2 months. Enrolled patients had low-risk [LR] (n = 18), favorable intermediate-risk [FIR] (n = 78), and unfavorable intermediate-risk [UIR] (n = 88) PC. Four-year rates of BCF free survival were 93.5% (95% C.I. 89-98%), 94.4% (89-100%), 92.5% (86-100%), and 93.8% (88-100%) in the overall group and the LR, FIR, and UIR cohorts, respectively (logrank p>0.4). The incidence of acute grade 2 or higher gastrointestinal (GI) and urologic toxicities were 3.8% and 12.5%, respectively. The 4-year incidence of late grade 2 or higher urologic and GI toxicity was 7.6% (4-13%) and 13.6% (9-20%), respectively. One late grade 3 GI toxicity was reported. All late toxicities were transient. Patient reported IPSS, IIEF, and EPIC scores had no significant long term changes following completion of HFPT.\n\n\nCONCLUSIONS\nHFPT is associated with low rates of toxicity and does not appear to negatively impact 4-year patient reported urinary and bowel health. Further comparative analyses are warranted to better understand differences between proton and photon HFRT.