Dose-volume relationships between enteritis and irradiated bowel volumes during 5-fluorouracil and oxaliplatin based chemoradiotherapy in locally advanced rectal cancer

Purpose. Radiation enteritis is the main acute side-effect during pelvic irradiation. The aim of this study was to quantify the dose-volume relationship between irradiated bowel volumes and acute enteritis during combined chemoradiotherapy for rectal cancer. Material and methods. Twenty-eight patients with locally advanced rectal cancer received chemoradiotherapy. The radiation therapy was given with a traditional multi-field technique to a total dose of 50 Gy, with concurrent 5-Fluorouracil (5-FU) and oxaliplatin (OXA) based chemotherapy. All patients underwent three-dimensional CT-based treatment planning. Individual loops of small and large bowel as well as a volume defined as whole abdomen'' were systematically contoured on each CT slice, and dose-volume histograms were generated. Diarrhea during treatment was scored retrospectively according to the NCI Common Toxicity Criteria scale. Results. There was a strong correlation between the occurrence of grade 2 + diarrhea and irradiated small bowel volume, most notably at doses > 15 Gy. Neither irradiated large bowel volume, nor irradiated whole abdomen'' volume correlated significantly with diarrhea. Clinical or treatment related factors such as age, gender, hypertension, previous surgery, enterostomy, or dose fractionation (1.8 vs. 2.0 Gy/fraction) did not correlate with grade 2 + diarrhea. Discussion. This study indicates a strong dose-volume relationship between small bowel volume and radiation enteritis during 5-FU-OXA-based chemoradiotherapy. These findings support the application of maneuvers to minimize small bowel irradiation, such as using a belly board'' or the use of IMRT technique aiming at keeping the small bowel volume receiving more than 15 Gy under 150 cc.