Selective Neck Dissection Under Multimodal Assessment for N3 Nasopharyngeal Carcinoma After Radiotherapy

The goal of this phase I clinical trial is to evaluate the safety and feasibility of a multimodal evaluation-guided surveillance-intervention strategy in patients with newly diagnosed N3 nasopharyngeal carcinoma. The main questions it aims to answer are: * Is the multimodal evaluation-guided surveillance-intervention approach safe for patients? * Is this approach feasible for identifying and managing residual cervical lymph nodes after radiotherapy? Participants receive standard chemoradiotherapy. After treatment, they undergo follow-up evaluation using clinical assessment, conventional imaging, Epstein-Barr virus DNA testing, and contrast-enhanced ultrasound. Participants with suspicious residual cervical lymph nodes identified by multimodal evaluation and considered suitable for surgical intervention undergo selective neck dissection.