Cochlea sparing effects of intensity modulated radiation therapy in head and neck cancers patients: a long-term follow-up study

Background: Radiation to the inner ear may lead to (irreversible) sensorineural hearing loss. The purpose of this study was to evaluate the long-term effect of radiotherapy on hearing in patients treated with Intensity Modulated Radiation Therapy (IMRT), sparing the inner ear from high radiation dose as much as possible. Methods: Between 2003 and 2006, 101 patients with head and neck cancer were treated with IMRT. Audiometry was performed before, short-term, and long-term after treatment. Data were compared to normal hearing levels according to the International Organisation for Standardization (ISO). Statistical analysis was done using repeated measurements. None of the patients received chemotherapy. Results: In 36 patients an audiogram at long-term follow-up (median 7.6 years) was available. The mean dose to the cochlea was 17.8 Gy (1.0 66.6 Gy). A hearing deterioration of 1.8 dB at Pure Tone Average (PTA) 0.5 1 2 kHz (p = 0.11), 2.3 dB at PTA 1-2-4 kHz (p = 0.02), and 4.4 dB at PTA 8-10-12.5 kHz (p = 0.01) was found. According to the ISO, the expected age-related hearing loss was 2.7, 4.8, and 8.8 dB at PTA 0.5-1-2 kHz, 1-2-4 kHz, and 8-10-12.5 kHz, respectively. Conclusions: After IMRT with radiation dose constraint to the cochlea, potential long-term adverse effects of IMRT remained subclinical. The progressive hearing loss over time was mild and could be attributed to the natural effects of ageing. Therefore, we recommend that a dose constraint to the cochlea should be incorporated in the head and neck radiotherapy protocols.