Prognostic Value of the Integrated PET/MRI in Patients With Nasopharyngeal Carcinoma

1. Background:

Nasopharyngeal carcinoma (NPC) has a higher local tumor control rate but a higher incidence of distant metastasis compared with squamous cell carcinomas of other regions of the head and neck. Thus, it's usually considered a distinct study group. A reliable clinical prognostic factor for NPC patients is still lacking. Positron emission tomography (PET) with 2- [fluorine- 18]fluoro-2-deoxy-D-glucose (18F-FDG)/computed tomography (CT) has been used extensively for diagnosis and assessment of prognosis in NPC in recent years. Several PET-derived imaging parameters such as standardized uptake value (SUV), metabolic tumor volume (MTV), or total lesion glycolysis (TLG) have been proposed as potential prognosticators in NPC. MRI functional parameters also play a role to assess the cellular or molecular change of head and neck cancer. Diffusion-weighted MR imaging (DWI) is a technique, which can quantify the diffusion of water molecules in tissues using apparent diffusion coefficient (ADC). ADC is inversely correlated with cellular density. Dynamic contrast-enhanced perfusion MR imaging (DCE-MRI) is another MRI technique based on sequential imaging obtained during the passage of a contrast of agent through the tissue. It enables probing the microvascular environment in the tumor tissue.

Integrated PET/MRI is a new imaging modality, which can simultaneously acquire PET and MRI images. Traditionally, PET and MRI images were acquired on different dates and were fused by commercial software. Problems caused by a separate system include SUV or MRI parameters were reported to be different if the scans were acquired on different days. Simultaneous acquisition of PET and MRI images would solve these problems. 2. Aim: The investigators conduct this prospective study to investigate the roles of integrated PET/MRI imaging parameters for predicting treatment outcomes and prognosis in patients with NPC. 3. Study design:

Patients: All patients receive whole-body 18F-FDG PET/MRI following 18F-FDG-PET/CT on the same day. For tumor staging, the 7th edition of the American Joint Committee on Cancer (AJCC)/Union for International Cancer Control (UICC) cancer staging system is used. The patients with stage I disease are treated with definitive radiation therapy alone, while patients with stage II-IVB are treated with concurrent chemoradiotherapy. Patients with metastatic disease (stage IVC) are treated with standard platinum-based chemotherapy.

18F-FDG PET/CT: All study patients fast for at least 6 h before 18F-FDG PET/CT imaging. Scans are performed using a Biograph mCT scanner (Siemens Medical Solutions, Malvern, PA, USA) consisting of a four-ring PET scanner (axial field-of-view [FOV] = 22.1 cm, transaxial FOV = 70 cm) and a 40-section CT scanner.