An MRI scan will also be done at the same time as each of the 2 FLT-PET scans done for this research study. The two MRI scans performed will also help give more information about the patient's tumor that is not routinely provided with a routine clinical scan, such as blood flow through the tumor or metabolic activity in the tumor. The information from these special MRI scans may provide more information about the blood supply to the tumor and how this changes in response to treatment. In addition, the MRI scans along with the FLT-PET scans may help how to distinguish inflammation due to radiation therapy from tumor growth.