Hearing loss after radiotherapy for pediatric brain tumors: effect of cochlear dose.

PURPOSE: To determine the effect of cochlear dose on sensorineural hearing loss in pediatric patients with brain tumor treated by using conformal radiation therapy (CRT). PATIENTS AND METHODS: We studied 78 pediatric patients (155 ears) with localized brain tumors treated in 1997-2001 who had not received platinum-based chemotherapy and were followed up for at least 48 months. They were evaluated prospectively by means of serial pure-tone audiograms (250 Hz-8 kHz) and/or auditory brainstem response before and every 6 months after CRT.
RESULTS: Hearing loss occurred in 14% (11 of 78) of patients and 11% (17 of 155) of cochleae, with onset most often at 3-5 years after CRT. The incidence of hearing loss was low for a cochlear mean dose of 30 Gy or less and increased at greater than 40-45 Gy. Risk was greater at high frequencies (6-8 kHz). In children who tested abnormal for hearing, average hearing thresholds increased from a less than 25 decibel (dB) hearing level (HL) at baseline to a mean of 46 +/- 13 (SD) dB HL for high frequencies, 41 +/- 7 dB HL for low frequencies, and 38 +/- 6 dB HL for intermediate frequencies.
CONCLUSIONS: Sensorineural hearing loss is a late effect of CRT. In the absence of other factors, including ototoxic chemotherapy, increase in cochlear dose correlates positively with hearing loss in pediatric patients with brain tumor. To minimize the risk of hearing loss for children treated with radiation therapy, a cumulative cochlear dose less than 35 Gy is recommended for patients planned to receive 54-59.4 Gy in 30-33 treatment fractions.