Prophylactic Radiotherapy Optimization for Enhanced Thyroid Function Protection in NPC

Inclusion Criteria: 1\. Male or female, aged 18-70 years; 2. Pathologically confirmed nasopharyngeal carcinoma; 3. No positive lymph nodes in unilateral or bilateral regions III and IVa; 4. Clinical stage I-IVa (AJCC/UICC 8th edition), with no evidence of distant metastasis; 5. Normal thyroid function; 6. ECOG performance status of 0-1; 7. Treatment-naïve patients who have not received any prior antitumor therapy; 6. No contraindications to radiotherapy or chemotherapy; 9. Adequate organ function, meeting the following criteria: Hematologic criteria: WBC ≥ 4.0 × 10⁹/L, ANC ≥ 1.5 × 10⁹/L, PLT ≥ 100 × 10⁹/L, HGB ≥ 90 g/L (no transfusion, blood products, or hematopoietic growth factors used within the past 7 days); Biochemical criteria: ALT and AST \< 1.5 × ULN, ALP \< 2.5 × ULN, total bilirubin \< ULN, BUN and creatinine ≤ 1.5 × ULN or creatinine clearance rate ≥ 60 mL/min (calculated using the Cockcroft-Gault formula). 10\. Voluntarily agreed to participate in the study, signed the informed consent form, demonstrated good compliance, and agreed to follow-up. Exclusion Criteria: 1. History of other malignant tumors (excluding basal cell carcinoma/squamous cell carcinoma of the skin or cervical carcinoma in situ); 2. History of radiotherapy (excluding radiotherapy outside the planned target area for conditions such as melanoma); 3. History of neck surgery; 4. Any severe comorbidities that may pose risks to the study or affect compliance, such as unstable heart disease requiring treatment, kidney disease, chronic hepatitis, poorly controlled diabetes (fasting blood glucose \> 1.5 × ULN), or psychiatric disorders; 5. History of hyperthyroidism, hypothyroidism, or immune-related thyroid disorders; 6. Other family or social factors, as judged by the investigator, may force the study's early termination, compromise patient safety, or affect the collection of trial data.