Effect of Radiotherapy on Retro-Cochlear Auditory Pathways

Abstract

The cochlea may be damaged by modern conventional radiotherapy (RT) for head and neck cancers when the ear is included in the radiation field. It is unclear however, if the retro-cochlear auditory pathways are affected as well, which has clinical significance in cochlear implantation. This study aims to investigate the integrity of the retro-cochlear auditory pathways in patients who had received RT for nasopharyngeal carcinoma. Prospective study. Patients who were newly diagnosed with nasopharyngeal carcinoma and treated by RT alone were studied. Evoked response audiometry and PTAs were carried out prior to and after RT (at 3, 18, and 48 months postRT). In addition, evoked response audiometry was also performed during the 3rd, 5th, and 7th week of RT. Waves 1 to 5, 1 to 3, and 3 to 5 latencies were measured. The values recorded during and postRT were compared with those recorded before RT. In addition, a subset of ears that demonstrated postRT sensorineural hearing loss were identified so that their respective wave 1 to 5 interwave latencies could be similarly compared. Wilcoxon signed ranks test was used in the statistical analysis. To confirm that the cochlea and internal auditory meatus receive significant doses of radiation, the RT treatment plans of nine other nasopharyngeal carcinoma patients treated by the same RT technique were analyzed to derive dose-volume histograms of these structures. Twenty-seven patients (20 males and 7 females) with a mean age of 51.2 (range 36-75) years participated in the study. There was no statistically significant difference in waves 1 to 5, 1 to 3, and 3 to 5 interwave latencies recorded during RT and postRT as compared with those recorded before RT (P > .05). Pre- and postRT wave 1 to 5 latencies of the 16 ears that had postRT hearing deterioration were also not statistically significant (P = .366). The mean radiation doses delivered to the cochlea and internal auditory meatus ranged from 24.1 to 62.2 Gy and 14.4 to 43.4 Gy, respectively. This study suggests in patients who have had RT for nasopharyngeal carcinoma, the retro-cochlear auditory pathways are functionally intact even in the longer term.