Dose-volume factors associated with ear disorders following intensity modulated radiotherapy in nasopharyngeal carcinoma

This study is to identify significant dosimetric parameters for ear disorders in nasopharyngeal carcinoma (NPC) patients treated with intensity modulated therapy only. Ninety-seven patients with NPC were retrospectively reviewed. Organs at risk (OARs) in the auditory apparatus were contoured. Dose-volume histogram parameters were generated for the Eustachian tube (ET), tympanic cavity (TC), mastoid air cells, vestibular apparatus, cochlea and internal auditory canal (IAC). Ear disorders were rated 0 (none), 1 (mild) or 2 (severe) by a clinician blinded to radiation doses; Grade 2 ear disorders was the study end-point. Multivariate analysis revealed ET. D-30 (dose to 30% of ET volume) >52.75 Gy and M. D-0.5CC (dose to 0.5 ml of mastoid volume) >41.04 Gy (OR = 3.77, P=0.012 and OR = 1.27, P = 0.033, respectively) were associated with Grade 2 ear disorders. Our results demonstrated that post-irradiation ear disorders remain a common late toxicity in NPC after IMRT. ET.D-30 and M. D-0.5CC should be considered during IMRT treatment plan optimization, review and approval.