Abstract: Background and purpose: In 2013, the official journal of European Society of Radiotherapy & Oncology (ESTRO) - Radiotherapy & Oncology published the updated version of Consensus Guidelines of Delineation of the neck node levels for head and neck tumors, which contributed to the standardization of description of neck nodal metastasis, as well as reduction of treatment variations from various institutions. This study applied this updated guidelines to analyze the patterns of lymph node metastasis of nasopharyngeal carcinoma and explore the prognostic value of the radiologic characteristics of nodes, in order to provide evidence for future revision of N staging system. Methods: A total of 656 patients from Jan. 2009 to Dec. 2010 were retrospectively recruited to analysis. All were pathologically diagnosed as non-metastatic nasopharyngeal carcinoma, treated with intensity-modulated radiotherapy. All patients received a pretreatment MRI scan. We retrospectively reviewed the MRI imaging of 656 patients and mapped the lymph node metastasis using the 2013 International Consensus Guidelines. Results: Median follow-up was 46.9 months. Four-year local recurrence-free survival, nodal recurrence-free survival, distant metastasis-free survival, disease-free survival and overall survival was 91.3%, 95.1%, 87.7%, 78.5% and 92.8%, respectively. The most common metastatic node levels were level Ⅱ (76.2%) and level Ⅶa (65.1%), followed by level Ⅲ (50.4%), Ⅴa(17.5%) and Ⅳa (11.7%). There was a very low incidence of node skipping (1.0%). Cervical nodal necrosis was observed in 46.4% of patients with positive nodes and extracapsular spread was noted in 74.4% of them. Univariate analysis showed that bilateral nodal involvement, greatest dimension of positive nodes (≥6 cm), central nodal necrosis, T stage and N stage were prognostic factors for disease-free survival and distant metastasis-free survival (P<0.05). Extracapsular spread showed a trend to correlate with poor distant metastasis-free survival (P=0.060). The involvement of lower neck levels (below the caudal border of cricoid cartilage) did not have a significant impact on disease-free survival and distant metastasis-free survival. In multivariate analysis, T stage and greatest dimension of nodes (≥6 cm) were independent prognostic factors for distant metastasis-free survival (P<0.05). T stage, greatest dimension of nodes (≥6 cm) and central nodal necrosis were independent prognostic factors of disease-free survival (P<0.05). Conclusion: This study demonstrates the patterns of lymph node metastasis of nasopharyngeal carcinoma based on 2013 International Consensus Guidelines. Bilateral nodal involvement, greatest dimension of positive nodes and central nodal necrosis had prognostic values on disease-free survival and distant metastasis-free survival. In our study, the involvement of lower neck levels was not proved to be a prognostic factor for disease-free survival and distant metastasis-free survival.

Key words: Nasopharyngeal carcinoma, Pattern of cervical nodal metastasis, Nodal necrosis, Extracapsular spread, Metastasis