Radiation Dose to Otologic Structures During Head and Neck Cancer Radiation Therapy

Abstract

Background: Otologic structures are often con· tained 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 30o/ o of patients experie~e sensorineural hearing loss on multimodality tlierapy 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 4of15 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 pa· tients 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 50o/o 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.

Effects of Piracetam Supplementation on Cochlear Damage Occuring in Guinea Pigs Exposed to Irradiation

“…24) Cochlear toxicity may occur, however, during radiation therapy of head and neck cancer. 1) In the literature we found that cochlear damage increased in proportion to RT dose. Kim and Shin 25) applied a single dose of 2, 6, 10, or 15 Gy to guinea pigs, and evaluated cochleas histopathologically.…”

Prospective study on the dose distribution to the acoustic structures during postoperative 3D conformal radiotherapy for parotid tumors

“…The cumulative risk of a significant persistent SNHL (> 15 dB) seems to stabilize within 2 years [10,21], whereas for severe SNHL (> 30 dB) the cumulative risk also continues to increase through the third and fourth year [10]. In a series with long follow-up (median of 13 years), stable rather than progressive character of SNHL was observed [18].…”

“…In any case, the cochlear dose was higher than the prescribed dose. In the series of pharyngeal and oral cavity cancer, Ondrey et al [21] observed up to 102% of prescribed dose administered to the cochlea. In the QUANTEC review, Bhandare et al [3] concluded that for conventionally fractionated radiotherapy, the mean dose to the cochlea should be limited to < 45 Gy, which was the case in all patients in our series.…”

Bacterial Biofilms May Explain Chronicity in Osteoradionecrosis of the Temporal Bone

“…The temporal bone is at risk mainly due to its superficial location and its proximity to the aerodigestive tract. A recent study modeling radiation dosimetry to otologic structures during radiation treatment for cancers of the nasopharynx, oral cavity, oropharynx, and hypopharynx clearly demonstrated ionizing radiation delivered to the temporal bone; the eustachian tube and cochlea were sites at greatest risk, especially with radiotherapy for nasopharyngeal carcinoma (9). Osteoradionecrosis usually arises when doses greater than 60 Gy are administered and has been reported to occur anywhere from several months to 40 years after completion of radiotherapy.…”