In a past study, FMISO PET scans were performed in 6 patients with rectal cancer that could not be operated on and that had spread to other areas. In this group of patients, FMISO PET scans were able to find the low oxygen areas in their tumors. But this study included only a few patients. In the present study, we want to use FMISO PET scans in patients who have tumors that can be operated on. This group of patients will have radiation, chemotherapy or both before they have their surgery. We want to see if FMISO PET can find low oxygen areas in this distinct group of patients.