Radiotherapy in addition to radical surgery in rectal cancer: evidence for a dose-response effect favoring preoperative treatment.

Abstract

This study explored the relationship between radiation dose and reduction in local recurrence rate after preoperative and postoperative radiotherapy in rectal cancer. All randomized trials initiated prior to 1988 comparing preoperative and postoperative radiotherapy with surgery alone or with each other were included. Local failure rates were available in 5626 randomized patients. The linear quadratic formula was used to compensate for different radiotherapy schedules. For preoperative radiotherapy, a clear dose-response relationship could be established. For postoperative radiotherapy, the range of doses was narrow, and a dose-response relationship could not be demonstrated. At similar doses, preoperative radiotherapy appeared to be more efficient in reducing local failure rate than postoperative. The only trial comparing preoperative with postoperative radiotherapy confirms this notion. A 15-20 Gy higher dose may be required postoperatively than preoperatively to reach similar efficacy. Neither approach alone significantly influences survival, although it is likely that a small survival benefit may be seen after preoperative radiotherapy. The information from the entire randomized experience suggests that preoperative radiotherapy may be more dose efficient than postoperative radiotherapy.