You will take the study drug/placebo, by mouth, every day for 7 weeks starting at the first week of radiation therapy. You may take the study drug/placebo with a full glass (8 ounces) of water. You may take it with or without food. If it causes an upset stomach, you should take it with food. If you have trouble swallowing the dose of study drug/placebo, you can open the capsule right before you take them. You should not lie down for at least 30 minutes after taking the study drug/placebo to prevent possible irritation of the inside of the esophagus, a known side effect. You will be given pamphlets with more information about how to take the study drug/placebo.