Maintenance Immunotherapy With Deferred Salvage Radiotherapy After Response to Chemoimmunotherapy in Recurrent Nasopharyngeal Carcinoma

Inclusion Criteria: 1. Age 18-70 years, any gender. 2. primary tumour recurrent T classificationT2-T4, regional lymph nodes recurrent N classificationN0-N2, no distant metastasis (recurrent M0); overall recurrent stage II-III according to the American Joint Committee on Cancer Union for International Cancer Control 9th edition stage-classification system. 3. Local recurrence (with or without regional recurrence) more than one year after radical treatment and unsuitable for surgery. 4. Pathologically confirmed non-keratinizing nasopharyngeal carcinoma (WHO type II or III). 5. Achieved complete response (CR) or partial response (PR) after 4-6 cycles of chemotherapy plus PD-1 inhibitor therapy. 6. ECOG performance status 0-1. 7. Expected survival ≥ 3 months. 8. No prior radiotherapy, chemotherapy, immunotherapy, or biological therapy for recurrent nasopharyngeal carcinoma 9. No contraindications to immunotherapy, chemotherapy, or re-irradiation. 10. 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 ≥ 50 mL/min Liver Function：Total bilirubin ≤ 1.5 × ULN，AST and ALT ≤ 2.5 × ULN. 11. 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. known pre-existing radiation-induced complications, including soft tissue necrosis, brain injury, neck fibrosis, or other radiation-induced complications of grade 3 or above 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 more than 1000 copies/mL or 200 IU/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.