PD-1 Inhibitor Plus Chemotherapy Followed by Immediate Versus Selective Re-irradiation for Locally Advanced Recurrent NPC

Inclusion Criteria: 1. Age 18-70 years, any gender. 2. Local recurrence (with or without regional recurrence) more than one year after radical treatment and unsuitable for surgery. 3. Pathologically confirmed non-keratinizing nasopharyngeal carcinoma (WHO type II or III). 4. Achieved complete response (CR) or partial response (PR) after 4-6 cycles of chemotherapy plus PD-1 inhibitor therapy. 5. ECOG performance status 0-1. 6. Expected survival ≥ 3 months. 7. No prior radiotherapy, chemotherapy, immunotherapy, or biological therapy for recurrent nasopharyngeal carcinoma 8. No contraindications to immunotherapy, chemotherapy, or re-irradiation. 9. Adequate organ function within 14 days before first dose, defined as: Hematology：Hemoglobin ≥ 90 g/L，ANC ≥ 1.5 × 10⁹/L，Platelet count ≥ 100 × 10⁹/L Renal Function：Creatinine ≤ 1.5 × ULN, or creatinine clearance (CrCl) / eGFR ≥ 60 mL/min Liver Function：Total bilirubin ≤ 1.5 × ULN，AST and ALT ≤ 2.5 × ULN, or ≤ 5 × ULN in the presence of liver metastases 10. INR or PT ≤ 1.5 × ULN, unless on therapeutic anticoagulation and values within therapeutic range，APTT ≤ 1.5 × ULN, unless on therapeutic anticoagulation and values within therapeutic range. Exclusion Criteria: 1. Presence of grade 3 or higher late radiation toxicity (excluding skin, subcutaneous tissue, and mucosa) at the time of recurrence 2. Prior anti-tumor therapy for recurrent nasopharyngeal carcinoma, including radiotherapy, chemotherapy, surgery, or immunotherapy. 3. Prior treatment with PD-1/PD-L1 or CTLA-4 inhibitors. 4. History of other malignancies within the past 5 years, except adequately treated basal cell carcinoma, squamous cell skin cancer, or in-situ cervical cancer. 5. Active autoimmune disease or history of autoimmune disease requiring systemic treatment (e.g., corticosteroids, immunosuppressants) within the past 2 years, except for stable hypothyroidism, type 1 diabetes mellitus, or resolved childhood asthma/atopy. 6. Known history of active pulmonary tuberculosis (TB). Suspected active TB must be excluded by chest X-ray, sputum examination, and assessment of clinical signs and symptoms. 7. Hepatitis B: HBsAg positive with peripheral blood HBV DNA ≥ 1000 copies/mL 8. Hepatitis C: HCV antibody positive, eligible only if HCV RNA is negative 9. HIV infection 10. Clinically significant cardiovascular disease (e.g., uncontrolled hypertension, unstable angina, myocardial infarction within 6 months, congestive heart failure ≥ NYHA class II, or serious arrhythmia). 11. Interstitial lung disease, non-infectious pneumonitis, or history of ≥ grade 2 pneumonitis. 12. Major surgery within 4 weeks before enrollment, or unhealed surgical wound. 13. Pregnant or breastfeeding women, or those planning pregnancy during the study period. 14. Known allergy or hypersensitivity to study drugs or their excipients. 15. Any condition that, in the investigator's judgment, would interfere with trial participation or interpretation of results.