Included are eligible patients with head and neck squamous cell carcinoma (T2, T3, T4, any N, M0) with tumor diameter ≥ 2,5 cm of the oral cavity, oropharynx, hypopharynx or larynx, planned to be treated with curative primary radiation treatment (+/- concurrent chemotherapy). Before treatment a standard planning [18F]FDG PET-CT will be performed, a blood sample is drawn and baseline [18F]HX4 PET scans will be performed. 18F-HX4 scans will be repeated after radiotherapy treatment with 20 +/- 4 Gy (approximately two weeks). Three months after the end of treatment a [18F]FDG PET scan will be performed.