Metastatic patterns of level II-V cervical lymph nodes assessed per vertebral levels in nasopharyngeal carcinoma

The current cervical lymph nodes classification system is not perfectly reasonable for radiotherapy of nasopharyngeal carcinoma (NPC). This study aimed to determine the metastatic patterns of level II-V lymph nodes in NPC by using vertebrae as anatomical landmarks.Four hundred and forty node-positive NPC patients were selected. Metastatic lymph nodes were diagnosed using positron emission tomography/computed tomography scan or magnetic resonance imaging. We evaluated univariate and multivariate logistic correlations between the vertebral levels of metastatic level II-V lymph nodes.The metastasis rate of level II-V lymph nodes gradually decreased from C2 (66.5%) and C3 (68.2%) to T1 (4.1%) vertebral levels. When assessed per vertebral level, 98.4% were non-skip metastasis. The interval of vertebral levels and distance between the inferior border of the tumor and the metastatic lymph nodes were similar in N1 and N2 patients. Univariate correlation analysis showed the metastasis of level II-V lymph nodes at each vertebral level was associated with the metastasis at any other vertebral level. In the multivariate analysis, metastasis at any one of the C2-C7 vertebral levels strongly and positively correlated with metastasis at two adjacent vertebral levels, including one level above and one below.This is the first study to report the distribution and non-skip metastatic patterns of level II-V lymph nodes assessed per vertebral levels in NPC. The low-risk clinical target volume could be reduced to two vertebral levels below the vertebral level of the metastatic level II-V nodes when both imaging modalities are available.