To evaluate whether individualized elective neck irradiation for nasopharyngeal carcinoma based on the vertebral level of metastatic lymph nodes can reduce the incidence of radiation-related adverse effects and improve patients' quality of life，without reducing survival.

A multicenter phase III noninferiority randomized trial (NCT02642107) showed that upper-neck irradiation at the uninvolved neck resulted in comparable regional control and survival rate to standard whole-neck irradiation in NPC, reduced late toxicity of hypothyroidism, dysphagia, and neck tissue damage, and improved quality of life, including fatigue and swallowing.

However, the vertical range of the upper neck is extensive, necessitating further reduction in the scope of prophylactic irradiation. By integrating MRI and PET-CT to accurately assess metastatic lymph nodes and their corresponding vertebral levels, the investigators identified a pattern of sequential lymph node metastasis descending along the vertebral body in the vertical direction. Further correlative analysis revealed that nodal metastasis at any one of the vertebral levels strongly and positively correlated with metastasis at two adjacent vertebral levels, including one level above and one below.

Considering this, the investigators propose the following scientific hypothesis: individualized elective neck irradiation for nasopharyngeal carcinoma based on the vertebral level of metastatic lymph nodes can reduce the incidence of radiation-related adverse effects and improve patients' quality of life, without reducing survival. The investigators thus conduct a multicenter randomized phase 3 trial to verify their hypothesis.

Inclusion Criteria:

• The eligibility criteria are: newly diagnosed, untreated, non-distant metastatic, and non-keratinizing NPC; nodes are diagnosed with PET/CT and MRI; staged as T1-4N0-2 or N3 category of non-bilateral lower-neck node metastasis; aged between 18 and 70 years; Karnofsky performance-status score > 70; adequate haematological function, with a leucocyte count > 4 × 109/L, haemoglobin > 90 g/L, and a thrombocyte count > 100×109/L

Exclusion Criteria:

• The exclusion criteria include: previous chemotherapy treatment, surgery (except diagnostic) or radiotherapy to the neck or nasopharyngeal regions; previous malignancy; lactation or pregnancy; or severe coexisting illness.