Postoperative irradiation for rectal cancer increases the risk of small bowel obstruction after surgery.

Objective: To determine the risk of small bowel obstruction (SBO) after irradiation (RT) for rectal cancer

Background: : SBO is a frequent complication after standard resection of rectal cancer. Although the use of RT is increasing, the effect of RT on risk of SBO is unknown.

Methods: We conducted a retrospective cohort study using Surveillance, Epidemiology, and End Results cancer registry data linked to Medicare claims data to determine the effect of RT on risk of SBO. Patients 65 years of age and older diagnosed with nonmetastatic invasive rectal cancer treated with standard resection from 1986 through 1999 were included. We determined whether patients had undergone RT and evaluated the effect of RT and timing of RT on the incidence of admission to hospital for SBO, adjusting for potential confounders using a proportional hazards model.

Results: We identified a total of 5606 patients who met our selection criteria: 1994 (36%) underwent RT, 74% postoperatively. Patients were followed for a mean of 3.8 years. A total of 614 patients were admitted for SBO over the study period; 15% of patients in the RT group and 9% of patients in the nonirradiated group (P < 0.001). After controlling for age, sex, race, diagnosis year, type of surgery, and stage, we found that patients who underwent postoperative RT were at higher risk of SBO, hazard ratio 1.69 (95% CI, 1.3-2.1). However, the long-term risk associated with preoperative irradiation was not statistically significant (hazard ratio, 0.89; 95% CI, 0.55-1.46).

Conclusions: Postoperative but not preoperative RT after standard resection of rectal cancer results in an increased risk of SBO over time.