Non-contrast-enhanced computed tomography attenuation in the parotid glands before radioiodine therapy for thyroid carcinoma could be a predictor of radiovulnerability.

OBJECTIVE: This study aimed to determine a predictive factor for the effect of radioiodine therapy (RIT) on salivary gland dysfunction through a multiple regression analysis.

METHODS: We retrospectively assessed 40 patients with thyroid carcinoma, including 13 men (age range, 21-80 years) and 27 women (age range, 28-75 years), who underwent total thyroidectomy and were treated with RIT. We used multiple regression analysis to evaluate whether factors such as age, sex, dose number, prescintigraphy grade, computed tomography (CT) attenuation, and CT volume of the salivary glands affected the postscintigraphy grade. Receiver operating characteristics analysis was performed for predicting worsening scintigraphy grade of the parotid glands in 20 patients after RIT.

RESULTS: The postscintigraphy grade of the parotid glands was positively associated with the dose number and prescintigraphy grade and negatively associated with CT attenuation (β=0.48, P<0.01; β=0.47, P<0.01; and β=-0.26, P<0.05, respectively; adjusted R2=0.50, P<0.05). In the submandibular glands, the postscintigraphy grade was only positively correlated with dose number (β=0.58, P<0.01; adjusted R=0.32, P<0.01). Area under the curve was 0.775 (P<0.05) and the cutoff CT attenuation was -18.8 HU (sensitivity 0.714 and specificity 0.846).

CONCLUSION: The RIT dose number, prescintigraphy grade, and CT attenuation may be important predictors of parotid gland dysfunction after RIT, whereas the dose number alone may be a significant predictor of submandibular gland dysfunction.