Increased chronic bowel complications with split-course pelvic irradiation.

Purpose: To assess the possible impact of various treatment factors including split-course versus continuous course treatment on the incidence of chronic bowel complications in patients receiving adjuvant pelvic radiotherapy.
Methods and Materials: A retrospective review was performed of records of 153 patients treated with adjuvant external beam pelvic radiation therapy without brachytherapy for endometrial and colorectal carcinomas. Continuous course radiotherapy was administered in 91 patients (59%) and 62 patients (41%) received split course treatment with a planned 2 week mid-treatment break. Mean pelvic dose and daily fraction size were 51.4 and 1.71 Gray, respectively. Multiple patient and treatment variables were assessed for their possible relationship to chronic bowel complications. Univariate and multivariate statistical analyses were carried out.
Results: Twenty-seven patients (18%) developed chronic bowel complications at a median interval of 12 months after radiotherapy. Of all factors analyzed, only the use of split course technique was associated with a significantly higher rate of chronic bowel injury and decreased complication-free survival (p = 0.009).
Conclusion: This study supports earlier suggestions that the use of split course rather than continuous course pelvic radiotherapy can increase late intestinal complication rates. Possible pathophysiologic mechanisms are discussed.