Impact of the Patterns of Retropharyngeal Lymph Node Metastasis on the Clinical Target Volume for the Radiotherapy Treatment of Nasopharyngeal Carcinoma

Objective: The aim of this study was to explore the patterns of retropharyngeal lymph node (RLN) metastasis in nasopharyngeal carcinoma (NPC) and their impact on the clinical target volume (CTV) delineation in radiotherapy. Methods: A total of 190 patients with untreated, nonmetastatic NPC received MRI scans of the nasopharynx and neck before treatment. The imaging characteristics of RLN metastasis and their relationships with the staging system were analysed. Results: A total of 121 patients developed RLN metastasis. The incidence rate of RLN metastasis was 63.7%. The RLN metastases of the 121 patients were distributed evenly in the lateral group, and no lymph node metastasis was observed in the medial group. Among the 121 patients, there were 66 cases of unilateral metastasis (54.5%) and 55 cases of bilateral metastasis (45.5%). The central position of the lymph nodes was mainly distributed in the C1 vertebra region. The differences in the RLN metastasis rate between different T stages, N stages and clinical stages were statistically significant (all P<0.01). Conclusion: Medial RLN metastasis is rarely observed in NPC and therefore does not require routine prophylactic irradiation with intensity-modulated radiation therapy (IMRT). This is an important issue for future research.