Prospective phase I study designed to determine the maximum tolerated dose of radiation therapy given in an accelerated fashion (2 Gy/fraction, 6 fractions/week) with concurrent chemotherapy. Intensity-modulated radiation therapy (IMRT) will be utilized to spare the esophagus. All patients on the dose escalation study will participate in additional assessments evaluating esophageal motion and esophageal toxicity from radiation therapy.