Predictors of radiotherapy-related gastrointestinal toxicity from anal cancer DP-IMRT: Secondary analysis of RTOG 0529.

460 Background: Radiation Therapy Oncology Group (RTOG) 0529 assessed feasibility of dose-painted intensity-modulated radiation therapy (DP-IMRT) to reduce the acute morbidity of chemoradiation with 5-fluorouracil (5FU) and mitomycin-C (MMC) for T2-4N0-3M0 anal cancer. This secondary analysis was performed to identify patient (pt) and treatment factors associated with acute and late gastrointestinal (GI) adverse events (AEs). Methods: RTOG 0529 treatment plans were reviewed to extract dose-volume data for tightly contoured small bowel (SB), loosely contoured anterior pelvic contents (APC), and uninvolved portions of colon outside the clinical target volume (UC). T-tests were performed to evaluate differences in the mean absolute volumes of each critical structure receiving doses ≥ 5 to 60 Gy (V5-V60) in 5 Gy increments between pts with and without ≥ grade (G) 2, acute and late GI AEs, and ≥G3 acute GI AEs using the NCI Common Terminology Criteria, version 3. Acute is defined as ≤ 90 days from the start of...