Dose constraints of optic nerves and chiasm in locally advanced nasopharyngeal carcinoma patients treated with intensity-modulated radiotherapy

Abstract

Objective To investigate the tolerated dose of the optic nerves and chiasm in patients with locally advanced nasopharyngeal carcinoma (NPC) treated with intensity-modulated radiotherapy (IMRT). Methods A retrospective analysis was performed on dose characteristics and the incidence of radiation optic neuropathy in 108 patients with locally advanced NPC treated with IMRT at D2>55 Gy in the optic nerves and chiasm in our hospital between May 2009 and December 2013. The Common Terminology Criteria for Adverse Events (CTCAE) Version 3.0 grading criteria were used for evaluating adverse reactions of the optic nerves and optic chiasm. A logistic regression analysis was performed to assess the risk factors for the development of radiation-induced optic neuropathy (RION). Results No patient had severe RION (grade 3-5), although 7 of the 108 patients had mild optic nerve disorder (grade 1-2). No patient-or treatment-related factors were found to be associated with the development of RION (P>0.05). With a median follow-up of 46 months (range, 13-91 months), the 3-year estimated overall survival, local recurrence-free survival, and distant metastasis-free survival rates were 90.0%, 94.5%, and 86.4%, respectively. Conclusions The dose constraint of<55 Gy derived for optic nerves and chiasm from conventional radiotherapy does not seem to apply to IMRT. For advanced NPC patients treated with IMRT, the dose constraints of optic nerves and chiasm might be relaxed in order to improve target coverage. Key words: Radiation induced optic neuropathy; Nasopharyngeal neoplasms/intensity-modulated radiotherapy; Dose constraints