The investigators hypothesize that treatment adaptation to biological and anatomical changes, occurring during treatment, can increase the chance of cure at minimized or equal radiation-induced toxicity in head and neck cancer patients. This trial compares standard intensity-modulated radiotherapy (IMRT), using only pre-treatment planning 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography to adaptive 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography voxel intensity based IMRT or volumetric-modulated arc therapy (VMAT) using repetitive per-treatment planning 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography for head and neck cancer.

Inclusion Criteria:

• Histologically confirmed squamous cell carcinoma of oral cavity, oropharynx, hypopharynx or larynx
• Primary unresectable tumor and/or patients that refused surgery
• Stages T1-4; T3-4 N0 or T(any) N1-3 for glottic cancer
• Multidisciplinary decision of curative radiotherapy or radiochemotherapy
• Karnofsky performance status >= 70 %
• Age >= 18 years old
• Informed consent obtained, signed and dated before specific protocol procedures

Exclusion Criteria:

• High risk Human Papilloma Virus (HPV)
• Treatment combined with brachytherapy
• Prior irradiation to the head and neck region
• History of prior malignancies, except for cured non-melanoma skin cancer, curatively treated in-situ carcinoma of the cervix or other cancer curatively treated and with no evidence of disease for at least 5 years.
• Distant metastases
• Pregnant or lactating women
• Creatinine clearance (Cockcroft-Gault) =< 60 mL/min
• Mental condition rendering the patient unable to understand the nature, scope and possible consequences of the study
• Patient unlikely to comply with protocol, i.e. uncooperative attitude, inability to return for follow-up visits, and unlikely to complete the study.