A new T staging system for nasopharyngeal carcinoma based on magnetic resonance imaging and intensity-modulated radiotherapy

Abstract

Objective To establish a new T staging system for nasopharyngeal carcinoma (NPC) based on magnetic resonances imaging (MRI) and intensity-modulated radiotherapy (IMRT). Methods A retrospective analysis was performed on the clinical data of 608 patients who were newly diagnosed with non-metastatic NPC by MRI and treated with IMRT in our hospital from 2008 to 2010. All patients were staged according to the 7th edition of the UICC/AJCC staging system for NPC. The survival rates were calculated using the Kaplan-Meier method and analyzed using the log-rank test. The Cox regression model was used for multivariate analyses. To deal with the deficiency in the current UICC/AJCC staging system, a new T staging system for NPC was established and systematically evaluated. Results The 5-year follow-up rate was 94.5%. The 5-year overall survival (OS), disease-free survival, local relapse-free survival (LRFS), and distant metastasis-free survival rates were 81.5%, 80.1%, 86.0%, and 81.1%, respectively. The univariate and multivariate analyses showed that the anatomic structures of nasopharynx, parapharyngeal space, and skull base were influencing factors for the OS rate (P=0.000-0.045). New T staging criteria were proposed based on the risk differences and survival curves: stage T1: invasion of the nasopharynx, parapharyngeal space, oropharynx, nasal cavity, skull base, and internal pterygoid muscle; stage T2: invasion of the external pterygoid muscle, paranasal sinus, intracalvarium, infratemporal fossa, and cranial nerves. The proposed T staging system achieved a good separation in both OS and LRFS curves. Conclusions The proposed new T staging system gives an objective prognostic prediction in patients with NPC, which provides an exploratory attempt toward a new clinical staging system for NPC. Key words: Nasopharyngeal neoplasms/intensity-modulated radiotherapy; Magnetic resonances imaging; Hazard discrimination; T staging system; Prognosis