In this multicenter, prospective, randomized, controlled, non-inferiority Phase III clinical trial, treatment-naïve patients with nasopharyngeal carcinoma (NPC) without metastasis will be enrolled for curative radiotherapy. The participants will be randomly assigned to two groups. The experimental group will receive online adaptive radiotherapy (ART) during the radiotherapy process, with a smaller PTV margin, while the control group will use original treatment plan during full-course radiotherapy, with a PTV margin of 3 mm. The study aims to compare the survival, adverse events, and quality of survival between the two groups, with the primary endpoint being the locoregional recurrence-free survival rate. The main objective is to determine the role of online ART in nasopharyngeal carcinoma, elucidating its potential to alleviate radiation toxicity in patients while ensuring treatment efficacy.

Inclusion Criteria:

1. Newly diagnosed nasopharyngeal carcinoma confirmed by pathology, with a histological classification of non-keratinizing carcinoma (according to the World Health Organization, WHO), pathological classification.
2. No evidence of distant metastasis (M0).
3. Age between 18 and 70 years.
4. Eastern Cooperative Oncology Group (ECOG) performance status score:0-1.
5. Undergoing radical intensity-modulated radiation therapy (IMRT).
6. No claustrophobia and able to remain in a fixed position for at least 30 minutes
7. Patients must be informed of the main content of this study, sign an informed consent form, and be willing and able to comply with the treatment, follow-up plan, laboratory tests, and other requirements specified in the study protocol.

Exclusion Criteria:

1. Histological types include squamous cell carcinoma or basal cell carcinoma.
2. Radiation therapy intended for palliative care.
3. History of malignant tumors, excluding adequately treated basal cell carcinoma, squamous cell carcinoma, and cervical intraepithelial neoplasia.
4. Pregnant or lactating women (women of childbearing age should undergo pregnancy testing; effective contraception should be emphasized during treatment.
5. Previous radical radiotherapy for nasopharyngeal cancer.
6. Primary and neck metastatic lesions treated with chemotherapy or surgery.
7. Presence of other serious underlying diseases that may pose a greater risk or affect compliance with the trial. Examples include unstable cardiac diseases requiring treatment, renal diseases, chronic hepatitis, poorly controlled diabetes (fasting blood glucose > 1.5×ULN), and psychiatric disorders.
8. Initial assessment of treatment efficacy more than 120 days after the end of radiotherapy.
9. Inability to undergo enhanced magnetic resonance imaging due to contrast agent allergies, claustrophobia.