Before beginning radiotherapy, a PET scan (series of pictures, 20 min. scan) will be performed at 2 hours after an intravenous injection of a small amount of radioactive traces drug, 18F-fluoromisonidazole (18F-FMISO) to observe the active hypoxia tumors areas. Upon completion of the 18F-FMISO PET scan, direct oxygen measurements will be obtained by placing a small needle into the tumor under computer tomographic (CT) guidance. The PET scan and needle measurements will be repeated every 4 weeks into the course of radiotherapy and again after the completion of radiotherapy. The measurement obtained by 18F-FMISO PET scanning (non-invasive technique) and by direct needle measurements (invasive technique) will be correlated with the eventual treatment outcome for future use.