A Randomized Controlled Trial of Spermidine for the Prevention of Radiation-Induced Xerostomia in Head and Neck Squamous Cell Carcinoma (Including Nasopharyngeal Carcinoma)

Inclusion Criteria: 1. Patients with histopathologically confirmed head and neck squamous cell carcinoma (including nasopharyngeal carcinoma). 2. Aged ≥18 years and ≤80 years. 3. ECOG performance status score ≤2. 4. Receiving radical radiotherapy or concurrent chemoradiotherapy with radiation dose \>50 Gy, where: Both parotid glands receive an average dose ≥25 Gy; or one gland receives a dose ≥25 Gy and the other receives any dose. 5. Blood routine parameters: hemoglobin ≥100 g/L, platelets ≥80×10⁹/L, white blood cell count ≥3.0×10⁹/L, absolute neutrophil count ≥1.5×10⁹/L. 6. Signed informed consent form. Exclusion Criteria: 1. History of xerostomia, Sjögren's syndrome, or other known systemic diseases predisposing to dry mouth. 2. Wheat allergy or gluten intolerance. 3. Suspected or confirmed physical occlusion of bilateral salivary gland ducts. 4. Prior history of head and neck radiotherapy. 5. Use of any medications or herbal supplements that may affect salivary function within the past 30 days, or planned/final use during the study period (e.g., amifostine, cholinergic agonists \[pilocarpine, cevimeline\], certain β-adrenergic antagonists, anticholinergic drugs, or other known salivary function modifiers). If using saliva substitutes, patients must abstain from use for at least 24 hours prior to saliva and questionnaire data collection. 6. Poor oral hygiene or severe periodontitis. 7. Poor compliance. 8. Pregnant or breastfeeding. 9. Other patients deemed unsuitable by the investigator (e.g., concurrent severe comorbidities, mental disability, or severe emotional/psychiatric disorders).