Radiotherapy (RT) for head and neck tumors has permanent, progressive, and dose-dependent effects on patients' hearing, report researchers.
Sensorineural hearing loss (SNHL) presents clinically at least 12 months after RT with initial loss of the high frequencies, report Sam Daniel (The Montreal Children's Hospital, Quebec, Canada) and team.
"A high frequency audiometry protocol should be consistently performed as a reliable method for early detection and follow-up of patients with SNHL," they say.
The findings come from a systematic review of articles published between 1970 and 2011 that reported on SNHL among patients who had received RT alone for head and neck tumors.
Daniel and team explain that previous studies of the literature lack conclusive evidence regarding the incidence and characteristics of hearing loss due to RT alone, as well as its associated risk factors. "Articles regarding SNHL after RT often include patients that are also treated with chemotherapy blurring the degree of hearing loss attributable to RT," they write.
The current study showed that the incidence of SNHL observed at frequencies above 4 kHz ranged from 27-95%, significantly more than that observed for speech frequencies (<4 kHz), which ranged from 0-85%.
Across all studies, a greater degree of SNHL was recorded at the shortest follow-up period (12 months) post-RT for frequencies above versus below 4 kHz and this trend was observed up to the maximum mean follow-up period of 8 years.
Overall, the team found that there was a consensus across the studies that the total radiation dose administered to the cochlea was the main risk factor for SNHL, and the minimum dose reported to be a risk factor was 45 Gy.
Gender and comorbidities such as diabetes and hypertension were not found to be risk factors for SNHL, while the risk effect of age was inconsistent throughout the studies.
"Further studies are needed to characterize the extent of damage to the retrocochlear pathways and its impact on hearing," say Daniel and team.
However, the authors conclude that patients receiving RT should be followed up for at least 1 year after RT with long-term serial audiometry.
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