Stage 2 of the study will evaluate both safety and efficacy. Sixty (60) subjects will be randomized in a 1:1 scheme to receive either placebo or EC-18 at the dose determined in Stage 1. Twice daily dosing (assuming EC-18 dose is greater than 500 mg) will begin on the first day of radiation (1 hour after the first fraction) and continue until the last day of radiation (approximately 7 weeks).