Effect of Radiotherapy on Vestibular Function Among Nasopharyngeal Carcinoma Patients

INTRODUCTION: Vestibular end-organs are deemed low-risk organs at risk (OAR) in the context of radiotherapy contouring in nasopharyngeal carcinoma (NPC) treatment. To date, existing literature on the effect of radiotherapy on vestibular function among post-irradiated NPC patients remains elusive. The main aim of this study is to determine the effect of radiotherapy on vestibular function, specifically the semicircular canal (SCC), in post-irradiated NPC patients. METHODS: A total of 31 post-irradiated NPC patients (10 patients in the prospective group and 21 patients in the cross-sectional group) were assessed by using the video head impulse test (VHIT) and adult dizziness handicap inventory (DHI) and compared with 36 healthy patients (control group). The vestibular ocular reflex (VOR) gain and the presence of saccade of individual SCCs were assessed and compared with the control group. VOR gain and the presence of saccade were correlated with the mean radiation dose of the cochlea. RESULTS: VOR gain of all SCCs among post-irradiated NPC patients was grossly reduced, significantly seen in all the right-sided semicircular canals and left anterior semicircular canal (p < 0.05), corresponding with a high DHI score. Persistently reduced VOR gain was demonstrated among subjects 3 months post-radiotherapy (p > 0.05). Right lateral SCC saccade was significantly positively correlated with mean radiation of cochlea (r = 0.667). CONCLUSION: Vestibular hypofunction was demonstrated in SCC among post-irradiated NPC patients and is found to be progressive as well as radiation dose-dependent.