Reduced-dose Radiotherapy for Stage III Nasopharyngeal Carcinoma Based on the Treatment Response

Inclusion Criteria: 1. Age: 18 Years to 65 Years; 2. Eastern Cooperative Oncology Group performance status ≤1; 3. Patients with newly diagnosed, histologically confirmed nasopharyngeal carcinoma, the pathological type is non-keratinising carcinoma; 4. Tumor staged as Stage III (AJCC 8th); 5. Patients' lymph node without adverse features (no central necrosis, no muscle/skin invasion, no lymph node fusion); 6. Normal bone marrow function: white blood cell count \> 4×10\^9/L, hemoglobin \> 90g/L, platelet count \> 100×10\^9/L; 7. Normal liver and kidney function: total bilirubin ≤ 1.5 × upper limit of normal (ULN), alanine transaminase and aspartate transaminase ≤ 2.5 × ULN, alkaline phosphatase ≤ 2.5 × ULN, creatinine clearance rate ≥ 60 ml/min; 8. Receive 3 cycles of indction chemotherapy (GP regimen + Camrelizumab); 9. Plasma EBV DNA after the second cycle of concurrent chemotherapy: 0; 10. Complete remission after 27 fractions of radiotherapy based on the MRI examination of the nasopharynx and neck (According to Response Evaluation Criteria in Solid Tumors 1.1); 11. Patients must sign informed consent and be willing and able to comply with the requirements of visits, treatment, laboratory tests and other research requirements stipulated in the research schedule; 12. Subjects with pregnancy ability must agree to use reliable contraceptive measures from screening to 1 year after treatment. Exclusion Criteria: 1. Hepatitis B virus surface antigen (HBsAg) positive and Hepatitis B virus DNA \> 1000 copies/ml; 2. Anti-hepatitis C virus positive; 3. Anti-human immunodeficiency virus (HIV) positive or diagnosed with acquired immune deficiency syndrome (AIDS); 4. Active tuberculosis: active tuberculosis in the past 1 year should be excluded regardless with treatment, history of active tuberculosis over 1 year should be excluded except that previous regulatory anti-tuberculosis treatment is proved; 5. Active, known or suspected autoimmune disease (including but not limited to uveitis, enteritis, hepatitis, pituitary, nephritis, vasculitis, hyperthyroidism, hypothyroidism and asthma requiring bronchiectasis). Exceptions are type I diabetes mellitus, hypothyroidism requiring hormone replacement therapy, skin disorders requiring no systemic treatment (such as vitiligo, psoriasis or alopecia); 6. Previous interstitial lung disease or pneumonia requiring oral or intravenous steroid therapy; 7. Chronic treatment with systemic glucocorticoid (dose equivalent to or over 10 mg prednisone per day) or any other form of immunosuppressive therapy. Subjects who used inhaled or topical corticosteroids were eligible; 8. Uncontrolled heart disease, for example: 1) heart failure (NYHA level ≥ 2), 2) unstable angina, 3) myocardial infarction in past 1 year, 4) supraventricular or ventricular arrhythmia requiring treatment or intervention; 9. Active infection requiring systemic treatment; 10. Previous or concurrent with other malignant tumors, except for adequately treated non-melanoma skin cancer, cervical carcinoma in situ and thyroid papillary cancer; 11. History of radiotherapy, except for non-melanoma skin cancer located outside the target volume of radiotherapy for nasophayngeal carcinoma; 12. Receive treatment for the local or regional disease other than that specified in the research plan; 13. Pregnant or lactating women (pregnancy test should be considered for women with sexual life and fertility); 14. Allergy to macromolecular protein preparations, or any component of Camrelizumab; 15. Receiving live vaccine within 30 days of the initial Camrelizumab; 16. Contraindications to MRI examination, for example: claustrophobia, allergy to MRI contrast; 17. History of psychotropic disease, alcoholism or drug abuse, and other situation assessed by the investigators that may compromise the safety or compliance of patients, such as serious disease requiring timely treatment (including mental illness), severe laboratory abnormalities, or family-social risk factors.