The primary research question to be answered in this project is "Are patients with locally-advanced head and neck cancer able to tolerate a PET-MRI scan when they are immobilised in a radiotherapy treatment shell?" This will be assessed by measuring the proportion of patients that complete the full scanning protocol and by obtaining participant feedback on their experience of completing the scan.

The secondary question is "Can a PET-MRI scan fused with a planning CT scan improve the accuracy in radiotherapy planning of patients with head and neck cancer? Accuracy will be assessed by:

1. Comparing the radiotherapy target volumes and radiotherapy plans with and without the use of a PET-MRI scan.
2. Comparing inter- and intra-observer variability in treatment contours with and without the use of a PET-MRI scan within and between oncologists and implications of that.

Inclusion Criteria:

1. Aged 18 years or over
2. Able to give informed written consent.
3. New diagnosis of biopsy-proven head and neck cancer.
4. WHO performance status ≤ 2.
5. MDT-recommended treatment with radical radiotherapy, with or without concurrent systemic therapy.
6. MRI and PET-CT staging scans for diagnosis.

Exclusion Criteria:

1. Known intolerance/sensitivity to 18F-2-deoxyglucose or gadolinium-containing contrast agents.
2. Claustrophobia or other contraindications to MRI.
3. Unable to pass through a 55 cm hula hoop.
4. Female patients that are pregnant or breastfeeding.
5. Unable to understand written or spoken English.
6. Patients not undergoing radical intent radiotherapy.
7. Patients with stage 4 or 5 chronic kidney disease or other biochemical abnormalities e.g. uncontrolled blood glucose levels which can have an impact on PET-MRI imaging or contrast administration.

IPD will not be available/shared outside the study