18F-FAZA–based imaging of hypoxia in planning of radiation therapy for head and neck tumor: FAZA PET (A and C), CT (B), and PET/CT (D). In B, large primary tumor (yellow arrow) and retro-pharyngeal lymph node metastasis (red arrow) demonstrate heterogeneous 18F-FAZA uptake. In C, blue region of interest depicts highest radiopharmaceutical uptake whereas yellow region delineates lowest. Dotted red line in D outlines tumor anatomically, and solid red line shows tumor, with a tumor-to-muscle ratio of more than 1.5. (Adapted with permission of (114).)