Analysis of gastrointestinal toxicity in patients receiving proton beam therapy for prostate cancer: A single-institution experience

Abstract Purpose We characterized both physician- and patient-reported rates of gastrointestinal (GI) toxicityin patients treated with proton beam therapy (PBT) at our institution for prostate adenocarcinomaand identified factors associated with toxicity. Methods and materials We treated 192 patients with PBT between July 2013 and July 2016. Included patients had ≥1 year of follow-up. Potential preexisting clinical and treatment-related risk factors for GI toxicitywere recorded. Common Terminology Criteriafor Adverse Eventsversion 4.0 was used to score toxicity. Expanded Prostate Cancer Index Composite ( EPIC) bowel domain questionnaires assessed patient-reported quality of life. Associations between grade (GR) 2+ toxicityand clinical, treatment, and dosimetric factors were assessed using Cox models and corresponding hazard ratios. Results The median follow-up was 1.7 years. Most of the observed GI toxicity(>90%) was in the form of rectal bleeding (RB). GR2+ GI toxicityand RB actuarial rates specifically at 2 years were 21.3% and 20.4%, respectively. GR3 toxicitywas rare, with only 1 observed RB event. No GR4/5 toxicitywas seen. The EPICbowel domain median score was 96 (range, 61-100) pretreatment, 93 (range, 41-100) at 1 year, 89 (range, 57-100) at 1.5 years, and 89 (range, 50-100) at 2 years. Anticoagulation use was the only factor selected during multivariate analysis for predicting GR2+ RB, with a resulting concordance index of 0.59 (95% confidence interval, 0.48-0.68; P = .088). Type of proton technology ( pencil beam scanningvs uniform scanning) and number of fields treated per day (1 vs 2) showed no significant difference in toxicityrate. Conclusions PBT was associated with acceptable rates of GR2+ transient GI toxicity, mostly in the form of RB, which correlated with anticoagulation use. High EPICbowel domain quality of life was maintained in the 2 years after treatment.