Vitamin D and Head and Neck Cancer: Impact on Toxicity and Prognosis

This study looks at whether vitamin D levels affect how well people with head and neck cancer tolerate radiation therapy and how their cancer responds. Researchers will measure vitamin D levels in patients before, during, and after radiation to find out if having enough vitamin D can help reduce side effects and improve treatment outcomes. **You may be eligible if...** - You have been diagnosed with head and neck cancer (squamous cell type) - Your cancer is locally advanced (has not spread to distant organs) - You are scheduled to receive radiation therapy (with or without chemotherapy) - You will receive radiation to both sides of the neck **You may NOT be eligible if...** - Your cancer has spread to distant parts of the body - You have a known disorder affecting how your body processes calcium or vitamin D Talk to your doctor to see if this trial is right for you.