THE VOLUME EFFECT IN RADIATION-RELATED LATE SMALL-BOWEL COMPLICATIONS - RESULTS OF A CLINICAL-STUDY OF THE EORTC-RADIOTHERAPY-COOPERATIVE-GROUP IN PATIENTS TREATED FOR RECTAL-CARCINOMA

Purpose: The purpose of this study was to quantify the correlation between irradiated small bowel volume and late occurring small bowel complications. Methods: Small bowel volumes in the high-dose region were measured using orthogonal barium films for 203 patients treated for rectal carcinoma with pelvic postoperative radiotherapy to 50 Gy in an EORTC multicentric study. Results: The 5-year estimate of late pelvic small bowel obstruction requiring surgery was 11%. No correlation between the irradiated small bowel volume and obstruction was detected. The actuarial 5-year estimate of chronic diarrhea varied from 31% in patients with irradiated small bowel volumes below 77 cm(3) to 42% in patients with volumes over 328 cm(3). This correlation was significant in the univariate and multivariate analysis (p = 0.025). The type of rectal surgery significantly influenced the incidence of chronic diarrhea and malabsorption, the actuarial 5-year estimate being 49% and 26% after low anterior resection and abdominoperineal resection, respectively (p = 0.04). Conclusions. This study demonstrated that there is a volume-effect in radiation-induced diarrhea at a dose of 50 Gy in 25 fractions. No volume-effect for small bowel obstruction was detected at this dose-level in pelvic postoperative radiotherapy. A review of the literature data on small bowel obstruction indicates that the volume effect at this dose level can only be demonstrated in patients who were treated with extended field radiotherapy (estimated small bowel volume 800 cm(3)) after intra-abdominal surgery.