Patients with stage III and IV head and neck squamous cell carcinoma treated on phase I and II chemoradiation trials with 70-Gy radiation combined with tirapazamine/cisplatin or cisplatin/fluorouracil ( 5FU ) , hypoxic imaging using [ 18F ] - misonidazole positron emission tomography and known HPV status ( by p16 immunohistochemistry ) were included in this sub-study .