Upper bound of IIb region in clinical target volume for intensity-modulated radiotherapy for nasopharyngeal carcinoma

Abstract

Objective To explore the upper bound of Ⅱb region in the clinical target volume (CTV) for intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC), and to establish a standard for personalized reduction in the range of Ⅱb region. Methods A retrospective analysis was performed on the IMRT results of 142 patients newly diagnosed with NPC who were admitted to our hospital from 2012 to 2014. According to the American Joint Committee on Cancer 2010 staging system, there were 8 patients with stageⅠ disease, 37 stage Ⅱ, 41 stage Ⅲ, and 56 stage Ⅳ. The distribution pattern of cervical lymph nodes in NPC was studied based on the imaging results. Comparison of the dose to parotid glands between patients with and without reduction in the range of Ⅱb region was made by t test and t' test. Results The metastasis rates of the most common diseased lymph nodes, lateral retropharyngeal lymph node and Ⅱb lymph node, were 75.4% and 67.6%, respectively. In the patients with metastases in Ⅱb region, 51.0% had high-risk positive lymph nodes and 6.3% had positive lymph nodes beyond the upper bound of Ⅱb region defined by the Radiation Therapy Oncology Group system. It was safe to narrow down Ⅱb region in patients who met the formulated standard. The D50 and V26 values for parotid glands were significantly reduced after optimization of CTV (P=0.000). Conclusions The upper bound of Ⅱb region, in principle, should reach the lateral skull base during the delineation of the cervical CTV for NPC. In order to protect the parotid glands, however, personalized reduction in the upper bound of Ⅱb region is recommended for patients who meet the formulated standard. Key words: Nasopharyngeal neoplasms/intensity-modulated radiotherapy; Clinical target volume; External expansion margin