The purpose of this study is to see if PET/CT scans that use a radioactive substance called [18F] fluorothymidine (FLT), can detect and monitor changes in the tumor. Radioactive substances are used with PET/CT scans to "see" cancer cells, and are also called radiotracers. FLT is a new radiotracer that has been given to people in prior studies. FLT PET/CT is an experimental scan unlike FDG (fluorodeoxyglucose) PET scan which is a standard clinical scan and is commonly used. The investigators would like to know if there is any evidence of early treatment response by obtaining FLTPET/ CT scans before and after treatment.