Imaging diagnosis of the medial group of retropharyngeal lymph nodes and the exploration of the optimization of target volume for protecting the swallowing structure in nasopharyngeal carcinoma

Abstract

Objective To clarify the diagnostic value of diffusion-weighed imaging (DWI) in the medial group of retropharyngeal lymph nodes in nasopharyngeal carcinoma, understand the clinical characteristics of retropharyngeal lymph nodes and explore the feasibility of optimizing the target volume of CTV60. Methods Clinical data of 437 patients with clinical stage Ⅰ-IVa nasopharyngeal carcinoma admitted to Jiangsu Cancer Hospital from 2011 to 2017 were retrospectively analyzed. All patients underwent magnetic resonance imaging (MRI), DWI (1 000 s/mm2) and enhanced CT scans to analyze the clinical characteristics of retropharyngeal lymph nodes and investigate the dosimetric advantage and safety of CTV60 lower margin on the upper margin of C2. Results The medial lymph nodes with a transverse diameter of 2.0-19.0 mm were detected 13 of 437 patients, and 53.8% of the lymph nodes were measured 2-5 mm in transverse diameter. The medial lymph nodes were distributed between the superior margin of C1 and 1/3 of C3.Its occurrence was related to N stage, double cervical lymph node metastases, especially the transverse diameter of cervical lymph node> 3 cm. The sensitivity of DWI, T2 and enhanced CT were 100%, 61.5% and 23.1%.After the special cases were excluded, the lower margin of CTV60 on the superior margin of C2 was separated. The radiation dose and volume of the swallowing structures were significantly decreased. The 5-year survival rate was 80% without recurrence in the optimized region. Conclusions The incidence of the medial group of retropharyngeal lymph nodes is low with a diameter of less than 5 mm. DWI possesses advantages in displaying the medial group of retropharyngeal lymph nodes. Isolating the lower margin of CTV60 from the superior margin of C2 is safe and feasible and has dosimetric advantages for protecting swallowing structure. Key words: Nasopharyngeal neoplasm; Lymph node; Diffusion-weighed imaging; Swallowing structure