Acute gastrointestinal toxicity and tumor response with preoperative intensity modulated radiation therapy for rectal cancer.

Background: Preoperative chemoradiotherapy (preopCRT) for locally advanced rectal cancer is associated with grade 3 or higher acute gastrointestinal (GI) toxicity. This study was conducted to determine whether intensity-modulated radiation therapy (IMRT) significantly reduces acute GI toxicity, compared to 3-dimensional conformal RT (3D-CRT) in preopCRT for rectal cancer.

Methods: A retrospective analysis was conducted of 48 patients treated between January 2002 and August 2010 with preopCRT for rectal cancer. 3D-CRT or IMRT was administered at a planned dose of 45-50.4 Gy to patients positioned prone on a bowel-displacement device. Data regarding patient and tumor characteristics, treatment, acute toxicity, and tumor response were collected. Comparisons of acute toxicity and treatment response between 3D-CRT and IMRT were performed with the Chi-square or Fisher's exact test.

Results: There were no significant differences in radiation dose, median age, race, gender, stage, type of concurrent chemotherapy, pathologic complete response (pCR), or type of surgery (lower anterior or abdominal perineal resection) between 3D-CRT and IMRT. There was a significant reduction in grade 2 or higher GI toxicity (3D-CRT, 60.7%; IMRT, 30%; P = .036) and grade 2 or higher diarrhea (3D-CRT, 42.8%; IMRT, 10%; P = .014). Two patients who underwent 3D-CRT required a treatment break (grade 3 diarrhea and grade 3 dehydration). Radiation duration was significantly less (IMRT, 35 days; 3D-CRT, 39 days; P ≤ .0001). pCR rates were 16.7% for 3D-CRT and 21.4% for IMRT (nonsignificant [NS]); pCR+microscopic residual rates were 57.1% for IMRT and 27.8% for 3D-CRT (P = .093).

Conclusion: Maximal bowel displacement with IMRT yields favorable acute GI toxicity and pathologic downstaging profiles, as compared to 3D-CRT in preoperative CRT for rectal cancer and warrants further prospective investigation.