Sarcopenia is a condition where the muscles become weak and thin. This study looks at how sarcopenia affects patients with head and neck cancer (HNC) treated with hadrontherapy, a type of particle therapy that uses tiny particles to attack cancer cells. The study will measure skeletal muscle mass at the C3 vertebral body (a bone in the neck) to see if it affects toxicity or side effects from treatment. The National Cancer Institute (NCI) uses the Common Terminology Criteria for Adverse Events (CTCAE) to measure these side effects, which could be acute (within 3 months) or late (more than 6 months after treatment).

• The study is for adults over 18 with head and neck cancer.
• Participants must be able to consent and have a good performance status (KPS > 80).
• Those with widespread cancer or certain mental health conditions are not eligible.