Dose escalation using dose-painted IMRT in locally advanced rectal cancer.

Abstract

582 Background: After preoperative chemo-radiation, clinical response and tumor pathologic downstaging showed a close correlation with improved outcomes. We report our initial experience in dose escalation using dose-painted intensity-modulated radiation therapy (DP-IMRT) in patients with locally advanced rectal cancer. Methods: Fifteen patients with locally advanced rectal cancer (T3-4,N0-1) were prospectively identified. Tumors were staged using the cTNM classification by PET/CT, EUS & MRI. All received preoperative 5-FU and DP-IMRT. Doses were prescribed as follows:56 Gy/2.0 Gy fractions (fxn) to the planning target volume (PTV) and 47.6Gy/1.7Gyfxn to elective nodal PTV. Surgery was performed 6-8 weeks after chemo-radiation. The surgical procedure was tailored to tumor downstaging. The choice of sphincter-preserving surgery was based on the distance between the lower tumor pole and the anorectal ring “ after” chemoradiation. All were reevaluated for tumor response, preoperatively by imaging studies (ycTNM) and by pathological staging (ypTN) following surgery. Acute and late toxicities were monitored by the treating physician. Results: All patients completed therapy. Tumors were in the lower 1/3 in 3 patients, middle 1/3 in 7, and upper 1/3 in 5. With preoperative endorectal US, PET/CT and MRI, the clinical staging of the tumors was: 13 (T3N0) and 2 (T4N0). Acute toxicity was limited to a moderate proctitis (RTOG acute toxicity scoring system, G1 ) in all patients, with two patients with tumors extending into the anal canal having G 3 dermatitis. Complete clinical response was obtained in 10 of 15 patients.All 15 underwent surgery; 6 had pathological pT0N0, 4 had residual micro foci of carcinoma (pT1N0), and 5 had residual disease limited to the muscularis propria (pT2N0). No difference in perioperative complications was seen. Conclusions: Preoperative dose-escalation using dose-painted radiation therapy (DP-IMRT) seems to be safe. Moderate local acute toxicity was seen with very low-lying tumors. This modality provides a high rate of tumor downsizing especially for patients with lesions in the lower 2/3 of the rectum with a possible potential for an increased ability to perform sphincter-preserving surgery.