IMRT is a type of 3-dimensional (3-D) radiation therapy that can focus radiation beams directly on the tumor itself. In this study, the IMRT is given using a standard radiation machine (ExaCT™ machine) that has a CT scanner attached to it. This machine is commonly used in patients with head and neck cancer. It gives the same radiation treatment as most of the other machines at M. D. Anderson. However, in addition to giving radiation treatments, it can also perform CT scans while the patient is in the same position on the treatment table, before the radiation therapy is given.