Effect of high dose radioiodine therapy on salivary gland function

Radioiodine (I-131) is used as an effective and non-invasive treatment for the thyroid malignancies. Salivary gland is one of the most affected non-target organ. The present study aims to quantitatively analyze the damage to the salivary glands caused due to radioiodine therapy (RIT) for thyroid ablation. A total of 20 patients (6 males and 14 females) with differentiated thyroid carcinoma were enrolled in the study. Baseline dynamic salivary scintigraphy was performed in all patients using 185-370MBq Tc-99m pertechnetate. Post therapy salivary scintigraphy was performed 10- 20 days after RIT (5- 7.4 GBq of I-131). Time activity curves obtained after pre and post therapy dynamic salivary scintigraphy were used for semi-quantitative analysis. Uptake ratio (UR), ejection fraction (EF%) and maximum accumulation (MA%) were calculated by drawing region of interest over composite image of each of parotid and submandibular glands. Paired t-test was used for comparison of the parameters obtained. Significant changes were observed in UR and EF% of both parotid and submandibular gland (p-value <0.05). No considerable changes were found in the value of MA% of left parotid gland and both submandibular gland in post-therapy scans in comparison to pretherapy scans (p-value >0.05). However, significant difference was observed in the MA% of right parotid gland (p-value=0.025). Based on the semiquantitative analysis, deterioration of salivary gland function after radioiodine therapy was found to be more in parotid gland in comparison to submandibular gland. (author)