Head and neck cancers (HNC) often receive radiotherapy as part of their treatment. However, unacceptable failure rates and severe side effects remain a challenge. The improvements in radiotherapy are closely related to improvements in medical imaging. Functional imaging, where intratumoural characteristics such as tumour oxygenation, metabolism, and blood vessel function can be quantified, offers possibilities to personalize the radiotherapy. In this study we will establish the clinical workflow for PET- and MRI-based radiotherapy in HNC by acquiring images prior to and during radiotherapy to develop new concepts for image-based biologically adaptive radiotherapy, both based on photon-based radiotherapy and also proton therapy, which soon will be available for cancer patients in Norway. The investigators aim to contribute towards further developments of personalised high-precision radiotherapy for HNC patients resulting in improved outcome, reduced side-effects and better quality of life.

Inclusion Criteria:

• willing and able to give full written consent according to the protocol approved by the Regional Ethics Committee
• histologically confirmed squamous cell carcinoma in the head neck region (pharynx, larynx, oral cavity or sinonasal area)
• locally advanced disease without sign of dissemination (T3/T4 and/or N1-3, M0) on diagnostic imaging
• scheduled for definitive radiotherapy with curative intent with or without concomitant chemotherapy
• adequate renal function: Creatinine clearance ≥ 60 ml/minute
• lymph node metastasis from cancer of unknown primary of the upper neck (i.e. level II-III) were PET/CT is negative outside the head-neck region can be considered for inclusion at the discretion of the study investigators.

Exclusion Criteria:

• general contraindications for MRI (pacemaker, aneurysm clips, any form of metal in the body, severe claustrophobia)
• serious comorbidity (including previous or othe cancer) that in the opinion of the investigator would compromise the patient's ability to complete the study of interfere with the evaluation of the study objectives (e.g. poorly controlled diabetes mellitus)
• histologically confirmed SCC of same or other origin within the last five years
• patient wants to withdraw for any reason during the study

Study population 1 consists of all patients who are referred to the "fast track" clinical pathway for HNC at St. Olavs hospital, approximately 130 patients per year for three years. Out of these, 60 patients are defined as study population 2, due to locally advanced head and neck cancer (HNC) of squamous cell histology scheduled for definitive (chemo)radiotherapy with curative intent.