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 bet ween irradiated small bowel volume and late occurring small bowel comp lications. Methods: Small bowel volumes in the high-dose region were m easured using orthogonal barium films for 203 patients treated for rec tal carcinoma with pelvic postoperative radiotherapy to 50 Gy in an EO RTC multicentric study. Results: The 5-year estimate of late pelvic sm all bowel obstruction requiring surgery was 11%. No correlation betwee n the irradiated small bowel volume and obstruction was detected. The actuarial 5-year estimate of chronic diarrhea varied from 31% in patie nts with irradiated small bowel volumes below 77 cm(3) to 42% in patie nts with volumes over 328 cm(3). This correlation was significant in t he univariate and multivariate analysis (p = 0.025). The type of recta l surgery significantly influenced the incidence of chronic diarrhea a nd malabsorption, the actuarial 5-year estimate being 49% and 26% afte r low anterior resection and abdominoperineal resection, respectively (p = 0.04). Conclusions. This study demonstrated that there is a volum e-effect in radiation-induced diarrhea at a dose of 50 Gy in 25 fracti ons. No volume-effect for small bowel obstruction was detected at this dose-level in pelvic postoperative radiotherapy. A review of the lite rature data on small bowel obstruction indicates that the volume effec t at this dose level can only be demonstrated in patients who were tre ated with extended field radiotherapy (estimated small bowel volume 80 0 cm(3)) after intra-abdominal surgery.