Preoperative radiotherapy in operable rectal cancer. The effect of preoperative radiotherapy (31.5 Gy in 3.5 weeks) in operable rectal cancer was examined with respect to resectability and prognosis after two surgical procedures, abdominoperineal resection, or low anterior resection. Preoperative radiation did not influence the surgeon's selection of low anterior resection, which was similar (40 percent) in each group. Radiation improved five-year survival probability and decreased the incidence of local recurrence significantly after low anterior resection. In contrast, no improvement of treatment results was found in patients treated by abdominoperineal resection after radiotherapy. 