Radiation dose to otologic structures during head and neck cancer radiation therapy

Background:Otologic structures are often contained within head and neck cancer radiation treatment ports. The dosimetry to otologic structures has not been routinely analyzed and radiation treatment planning does not currently attempt to specifically avoid the inner ear structures when dosimetry is calculated. Recent studies demonstrate that up to 30 of patients experience sensorineural hearing loss on multimodality therapy with cisplatin and radiation. Methods:In the current case series, radiation dosimetry to otologic structures was calculated from computed tomogram treatment plans on patients. Fifteen nasopharyngeal, oral cavity, oropharyngeal, and hypopharyngeal cancer patients were analyzed. Results:Between 8 and 102 of the total dose is delivered to the petrous bone/cochlea, with 4 of 15 patients getting more than 50 of the dose to at least one cochlea. The mastoid air cells received between 3 and 75 of the total dose, with higher doses being delivered to patients with bulky high neck metastases or nasopharyngeal tumors. The eustachian tubes received between 2 and 102 of the total dose, with 10 of 15 patients receiving more than 50 of the dose to this anatomic site. Conclusion:We conclude that the cochlea and eustachian tubes receive significant radiation during treatment, particularly in nasopharyngeal cancer patients. Careful design of radiation treatment ports may allow for the reduction of radiation to hearing structures.