The Study Of N Stagingsystemfor Nasopharyngeal Carcinoma Based On Intensity Modulated Radiotherapy And Rtog Guidelines For Lymph Node Levels

BACKGROUD & OBJECTIVE:Nasopharyngeal carcinoma(NPC) of lymph node metastasis has a high positive rate,and plays animportant role in thS definition of radiotherapy area,clinical staging and prognosis. Intensity modulated radiation therapy (IMRT) has become a mainstream treatment of nasopharyngeal carcinoma.7th edition UICC/AJCC N staging is subjective and mainly based on clinical examination of conventional two-dimensional radiation therapy, and fails to fit the changes in the diagnosic and treatment means.So this study was designed to explore the regulation for the distribution of metastatic lymph nodes of nasopharyngealcarcinoma, and evaluate the prognostic value of different nodal variable including laterality, size, extracapsular spread and necrosis based on MRI image and RTOG guidelines for lymph node levels of NPC patients treated with intensity modulated radiotherapy (IMRT), which may provide a new N staging system for clinical treatment and research.Methods:From Jan.2011 to Dec.2011,324 patients with newly diagnosed, histologically proven NPC and nonmetastatic at radiation oncology department of the First Affiliated Hospital of Guangxi Medical University with IMRT were retrospectively analyzed. All patients were received MRI scan of nasopharynx and neck before treatment.Reviewing all MRI information, physical examination and clinic records, reassessing the clinical staging by 7th UICC/AJCC staging system. The cervical lymph node metastasis was diagnosized according to Michiel and Lam criterion.The cervical lymph node levels were classified according to RTOG guidelines recommended in 2003 and improved in 2013. Then, Chi-square test was used to analyze the correlation between T stage and nodal metastasis rate and between nodal diameter and nodal extracapsular invasion. The actuarial rates were estimated using the Kaplan-Meier method and the differences were compared using the log-rank test.Multivariate analyses used the Cox proportional hazards model to formulate a new N staging.Results:Of 324 patients,269(83.0%) had nodal involvement. The distribution was as follows:1 in level Ib,221 in level II,82 in level III,14 in level IVa and Va,1 in level IVb,10 in level Vb,3 in level Vc,213 in retropharynx. Leap metastasis was 3.In these patients, a total of 912 postive nodes, including 626(68.6%)extracapsular spread nodes, were detected. The rate of nodal extracapsular invasion was higher when the axial diameter increased.No significant correlation was found between the scope of primary tumor and nodal involvement.The median follow-up time was 43(6-60)months. The 3-year overall survival(OS), disease free survival(DFS), relapse free survival(RFS)and distant metastasis free survival(DMSF)rates were 89.2%,85.8%,96.8% and 88.9%, respectively. Univariate and Multivariate analyses of 269 cases with positive cervical lymph node (CLN) revealed that retropharyngeal lymph node (RLN) status, CLN level and laterality were evaluated as independent prognosticators for prognosis, and CLN size, extracapsular spread and necrosis weren’t significant factor for prognosis.According to the Hazard ratio valyes calculated, the criteria of N stage were revised as follows:NO:no regional lymph node metastasis; N1:Ⅵa, or/and unilateral level (level Ⅱ>Ⅲ Va) involvement; N2:bilateral level (level Ⅱ、Ⅲ、Va) involvement; N3:level Ⅳa、Vb and the following area.Conclusion:The level Ⅱ and RLN were the most frequently involved regions, they had similar metastatic rate and were beth the firstecho node to metastases of nasopharyngeal carcinoma. Level I and the incidence of skip metastasis was lower. The cervical node involvement of nasopharyngeal carcinoma was spread orderly down the neck.The proportion of extracapsular spread of metastatic lymph nodes increased with axial diameter of lymph nodes-dependent. The relationship between T stage and nodal involvement has no statistical significance. The proposed N staging system is based on IMRT and RTOG guidelines for lymph node level, and provides a highly objective and predictive medthod for staging NPCs.