Rectal toxicity profile after transperineal interstitial permanent prostate brachytherapy: use of a comprehensive toxicity scoring system and identification of rectal dosimetric toxicity predictors.

Abstract

To better understand rectal toxicity after prostate brachytherapy, we employed the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE version 3.0), a comprehensive system with distinct and separately reported gastrointestinal adverse event items (unlike Radiation Therapy Oncology Group morbidity scoring), to evaluate item-specific postimplant rectal toxicities. We analyzed 135 patients treated with brachytherapy +/- hormonal therapy, using CTCAE v3.0 to score acute/late rectal toxicities (median follow-up, 41 months). Dosimetric parameters were evaluated for ability to predict toxicities. Use of CTCAE yielded a novel rectal toxicity profile consisting of diarrhea, incontinence, urgency, proctitis, pain, spasms, and hemorrhage event rates. No item had a < 5% Grade 1-2 acute toxicity rate (except spasms). Rectal dosimetry predicted late toxicities: for diarrhea, 5% Grade 1 toxicity rate for %V25 (percent of rectal volume receiving 25% of prescribed prostate dose) < or = 25% vs. 60% for %V25 > 25% (p < 0.001); for maximum toxicity, 10% Grade 1 toxicity rate for %V10 < or = 40% vs. 44% for %V10 > 40% (p = 0.007). A comprehensive understanding of item-specific postimplant rectal toxicities was obtained using CTCAE. Rectal %V25 > 25% and %V10 > 40% predicted worse late diarrhea and maximum toxicity, respectively.