Cochlear implants: Response to therapeutic irradiation

Purpose: To determine the response of cochlear implants ("bionic ears") to therapeutic irradiation. Methods and Materials: A patient with a cochlear implant was referred for p alliative cranial irradiation. As there were no published or manufacturer's data available regarding the response to radiation, implants were tested f or functional changes following irradiation. Cochlear implants were supplie d by Cochlear Ltd. Two units each of models CI22M, CI22M (with the second g eneration integrated circuit) and CI24M were irradiated with 4 MV X-rays, a nd an unirradiated unit of each model was used as a control. The implants w ere irradiated initially with 25 daily fractions to 50 Gy. To determine the response at higher doses, 10 Gy fractions were delivered to the same impla nts to 100 Gy, followed by a final fraction of 50 Gy (total dose 150 Gy). T he implants were tested after each 10 Gy, up to 100 Gy, and at 150 Gy. Seve ral indicators of functionality were assessed, including RF (radio frequenc y) link range, and stimulator output current. The radiation shielding effec t of the implants was also assessed. Results: Within the dose range less than or equal to 50 Gy, the stimulator output current of the CI22M units was the only parameter to change. At high er doses (to 150 Gy), changes in current output continued, and gradual loss of RF link range occurred in the CI22M units. The CI24M units showed chang es in output current to 100 Gy, and large changes at 150 Gy. Dose attenuati on by the implants was measured at 6% for ipsilateral single field 4 MV X-r ays. Conclusion: Our results suggest that patients with these cochlear implants can receive cranial irradiation with a low risk of implant failure. Changes in stimulator output current can be compensated simply by reprogramming th e speech map after the course of radiation treatment. (C) 1999 Elsevier Sci ence Inc.