The objective of this study was to evaluate the influence of dose on nasal localization of radioactive iodine-131 (I-131) following therapy for differentiated thyroid carcinomas.
Retrospective evaluation of all patients who underwent post-therapy I-131 whole body scintigraphy and single photon emission computed tomography was performed. Patients were divided into 2 groups; group A were treated with 100 millicurie (mCi) and group B with ≥150 mCi. Databases were reviewed for demographics, diagnosis, and administered dosage of I-131. Whole body scintigraphy images were retrieved and nasal uptake was analyzed and classified as nil to trace, low, moderate, and high uptake and corresponding single photon emission CTs were analyzed for radioactive nasal activity.
A total of 100 patients were studied, 50 in each of the groups. The M:F ratio was 1.1:1 (27:23) in group A and 1.5:1 (30:20) in group B. The mean age was 43.12 years and 54.6 years in groups A and B, respectively. Papillary carcinoma of the thyroid was the most common type accounting for 82% (41/50) of patients in group A and 62% (31/50) in group B. Imaging studies revealed nil to trace nasal activity in 80% (40/50) in group A as compared with 56% (28/50) in group B. None of the patients in group A showed high nasal uptake, whereas 4% (2/50) in group B demonstrated such high activity.
Intranasal localization of radioactive I-131 was significant in patients receiving a dose of ≥150 mCi. Intranasal localization may partly explain toxicity to nasolacrimal duct and may be a risk factor for subsequent development of nasolacrimal duct obstructions.