The effect of large single radiation doses on cochlear implant function: implications for radiosurgery.

The purpose of this study was to investigate the effect of large single doses of radiation on the function of a cochlear implant. A cochlear implant (Nucleus 24 k, Cochlear Ltd., Sydney, Australia) was implanted into a cadaver head and tested for functional changes following irradiation. Within 2 h, the device was given single fractions of 16.3 Gy, 6.2 Gy and 20 Gy with 6 MV photons. The size of the fractions was derived from maximum doses registered in linear accelerator-based radiosurgery of more than 300 patients treated for benign or malignant tumors at the Department of Radiation Therapy of the University Hospital of Freiburg. After each treatment an integrity test was performed testing the impedance and current output of the CI system. The total dose of 42.5 Gy caused no changes with regard to the tested parameters. The risk of implant failure seems to be low for Nucleus 24 k cochlear implants exposed to large single doses of radiation as used in radiosurgery.