Tolerance of the small bowel to therapeutic irradiation: A focus on late toxicity in patients receiving para-aortic nodal irradiation for gynecologic malignancies

Objective: The recently published Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) recommends dose constraints for acute small-bowel toxicity but does not fully address dose constraints for late small-bowel toxicity and the maximum dose tolerance of the small bowel. Radiation oncologists in practice frequently face a challenge when deciding what maximum point dose to accept in a patient's treatment plan. Given this lack of guidance for maximum radiation dose tolerance on the small bowel, we performed a literature search on the topic. Methods: We searched PubMed for English language publications up to December 2012 on pelvic and para-aortic lymph node (PALN) irradiation for gynecologic malignancies. The search was performed using the following key words: late small-bowel toxicity, cervical cancer, endometrial cancer, ovarian cancer, gynecologic malignancies, pelvic irradiation, PALN irradiation, extended-field radiation therapy. Relevant references were selected, and full articles were obtained for review. The predetermined criteria for deciding which studies to include were used. Results: With photon irradiation, the incidence of grade 3 or greater late small-bowel toxicity, including small-bowel obstruction, is 9% ± 7% after a median follow-up of 5 years and with mean pelvic and para-aortic/whole abdominal prescription doses of 50 ± 5 Gy and 40 ± 10 Gy, respectively. Our estimate for the small-bowel T10/5 would be the maximum point dose of 55 Gy. Conclusions: If possible, it is prudent to try to keep the maximum point dose to the small bowel at 55 Gy or less. Given the lack of substantial data to make firm guidelines, further studies are needed to clarify the dose-volume relationship for late toxicity. Dose escalation to PALN should continue to be used with caution.