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

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 (yc...