Purpose: To determine the relationship between acute gastrointestinal (GI) toxicity during the combined modality segment and the volume of small bowel in the pelvic radiation field in patients who receive either preoperative or postoperative therapy for rectal cancer.
Patients and methods: The patient population was derived from four consecutive phase I dose-escalation trials. Combined modality therapy included fluorouracil (5-FU), leucovorin ([LV] bolus daily x 5, days 1 and 29), and pelvic radiation.
Results: Twenty patients who received postoperative therapy had a larger volume of small bowel in the pelvic radiation field as compared with 60 who received preoperative therapy (462 +/- 129 v 212 +/- 44 cm3, P = .002). The most significant relationship between acute GI toxicity and volume of small bowel was seen in 12 patients who were treated on the preoperative sequential low-dose LV trial, all of whom received the maximum-tolerated dose (MTD) of 5-FU. The volume of small bowel in patients who experienced grade 3+ toxicity was 731 +/- 274 cm3, as compared with 145 +/- 58 in those who experienced grade 0 to 2 toxicity (P = .005). Likewise, logistic regression analysis showed that 26 patients who received the MTD of 5-FU had the most significant association between GI toxicity and volume of small bowel (P = .036).
Conclusion: Our data suggest that the volume of small bowel in the pelvic radiation field may be dose-limiting in the delivery of high-dose 5-FU when combined with LV and radiation therapy.