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MR evaluation of radiation otomastoiditis
R Nishimura1, Y Baba, R Murakami
1Department of Radiology, Kumamoto University School of Medicine, Honjo, Japan.
Summary
High radiation doses (50 Gy+) increase radiation otomastoiditis incidence. Limiting radiation fields, especially anterior and posterior to the clival line, can reduce this risk after radiotherapy.
Area of Science:
- Radiology
- Oncology
- Otolaryngology
Background:
- Radiotherapy for head and neck cancers can involve the temporal bone.
- Radiation otomastoiditis is a potential complication affecting the middle ear and mastoid air cells.
- T2-weighted MRI is used to assess changes in the temporal bone post-radiotherapy.
Purpose of the Study:
- To evaluate the incidence of radiation otomastoiditis using T2-weighted MRI.
- To correlate the incidence with radiation fields, doses, and intervals.
- To assess the relationship with clinical symptoms.
Main Methods:
- Follow-up MRI examinations of 270 ears from 114 patients.
- Scoring of middle ear and mastoid air cells on T2-weighted images for high signal intensity.
- Classification of radiation fields based on the clival line (anterior, posterior, or both).
Main Results:
- Incidence of radiation otomastoiditis increased with doses of 50 Gy or more.
- For doses <50 Gy, incidence was 18% (within 6 months), 13% (6-12 months), and 8% (>12 months).
- For doses ≥50 Gy, incidence exceeded 50% at any time point; high incidence was observed when fields included areas anterior and posterior to the clival line.
Conclusions:
- Radiation doses of 50 Gy or more significantly increase radiation otomastoiditis incidence.
- Limiting irradiation fields of the temporal bone to the smallest possible area is recommended for doses ≥50 Gy.
- The clival line serves as a useful landmark for reducing radiation fields during curative radiotherapy (60-70 Gy).