Background & objective: The application of intensity- modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC) requires a precise delineation of the nodal area and nodal clinical target volume (CTV) on computed tomography (CT) images,and the prerequisite is to find out the rules of CT-based distribution of metastatic lymph nodes of NPC. This study was designed to analyze the rules of CT-based distribution of nodal involvements of NPC according to the guidelines of nodal levels proposed by Radiation Therapy Oncology Group (RTOG).
Methods: From Jul. 2003 to Nov.2003, 259 newly diagnosed NPC patients received radiotherapy at Fudan University Affiliated Cancer Hospital. All patients had transversal contrast enhanced CT scan from base of skull to clavicle before treatment. Diagnostic radiologists and radiation oncologists together assessed the nodal distribution in each RTOG nodal level. Chi-square test was used to analyze the correlation between T stage and nodal metastasis rate. The neck was further divided into 3 regions by the verge of hyoid bone and the inferior border of cricoid cartilage to assess leap metastasis of nodes.
Results: A total of 218 patients (84.2%)had nodal involvement. The distribution was as follow: 0 in level Ia, 6 (2.8%) in level Ib, 115 (52.8%) in level IIa,192 (88.1%) in level IIb, 78 (35.8%) in level III, 20 (9.2%) in level IV, 65 (29.9%) in level V, 0 in level VI,157 (72.0%)in retropharynx, and 2 (0.9%) at preauricular area. Leap metastases were found in only 5 patients (2.3%). No significant correlation was found between T stage and nodal involvement.
Conclusion: NPC has a high probability of nodal metastases, nodes in level IIa,IIb, and retropharynx are most likely to be involved. Nodes metastasized mostly from the upper to the lower level, and from the proximal to the distal part, with a very low leap metastasis rate. The relationship between T stage and nodal involvement has no statistical significance.