Intraoperative electron beam radiation therapy for recurrent locally advanced rectal or rectosigmoid carcinoma. A multimodality approach of moderate-dose to high-dose preoperative radiation therapy, surgical resection, and intraoperative electron beam radiation therapy (IORT) has been used for patients with locally recurrent rectal or rectosigmoid carcinoma. The 5-year actuarial local control and disease-free survival for 30 patients undergoing this treatment program were 26% and 19%, respectively. The most important factor predicting a favorable outcome was complete resection with negative pathologic resection margins. The determinant local control and disease-free survival for 13 patients undergoing complete resection were 62% and 54%, respectively, whereas for 17 patients undergoing partial resection these figures were 18% and 6%, respectively. There did not appear to be a difference in local control or survival based on the original surgical resection (abdominoperineal resection versus low anterior resection). However, the likelihood of obtaining a complete resection after preoperative radiation therapy was higher in patients who had previously undergone a low anterior resection than patients undergoing prior abdominoperineal resection. For the 30 patients undergoing external beam irradiation, resection, and IORT, the most significant toxicities were soft tissue or sacral injury and pelvic neuropathy. Efforts to further improve local control are directed toward the concurrent use of chemotherapy (5-fluorouracil with and without leucovorin) as radiation dose modifiers during external beam irradiation and the use of additional postoperative radiation therapy. 