Assessment of Salivary and Lacrimal Gland Dysfunction after Radioiodine Therapy Using 99mTc-Pertechnetate Scintigraphy

Background: Iodine-131 (I-131) is an effective treatment for differentiated thyroid carcinomas (DTC) after surgery. Salivary and lacrimal gland dysfunction has been described in patients receiving high doses of 1-131 due to radiation damage to salivary and lacrimal glands. Objective: This prospective study was conducted to determine the short term effect of oral 1-131 therapy administered to thyroid cancer patients on the function of salivary gland by 99mTcpertechnetate scintigraphy with semiquantitative analysis and assessment of lacrimal gland affection. Methods: Twenty patients with post-surgical DTC (mean age, 45.6±9.7 y) were referred for 1-131 therapy (mean dose 196±108 mCi). All patients had no symptoms or signs or drug history of Sicca syndrome. Before and 8-12 months after 1131 therapy, salivary gland function was estimated by sequential salivary gland scintigraphy after an intravenous injection of 185 MBq (5 mCi) 99mTc-pertechnetate with lemon stimulation at 15th min post-injection. Regions of interest (ROIs) were drawn over the four parotid and submandibular glands. Time-activity curves were generated and semiquantitative functional parameters were calculated for each gland to obtain the time at maximum count (Tmax). Clearance fraction (CF) was also calculated. Mean values of the bilateral glands were used for data analysis. Lacrimal gland function was carried out by Schirmer's test done before and after 1-131 therapy; wetting of 5mm or less was considered abnormal. Results: Tmax and CF of parotid and submandibular glands were normal in all patients with no clinical symptoms of xerostomia at base line study. On follow-up, 7 patients reported variable severity of xerostomia. However, 12 patients showed deterioration of their salivary indices with significant difference in the Tmax and CF values between 2 studies (p 0.03, 0.01 for parotid and 0.02, 0.02 for submandibular, respectively). There was a significant positive correlation between the given 1-131 dose and Tmax values (r 0.66p 0.002 for parotid and r 0.71p 0.001 for submandibular). There was a significant negative correlation between the given 1-131 dose and CF values (r-0.48 p 0.03 for parotid and r-0.49 p 0.03 for submandibular). Abnormal Schirmer's test was documented in 5 patients; yet, non-significant (p=0.41). Correspondence to: Dr. Ahmed A. Kandeel, The Department of Nuclear Medicine (NEMROCK), Faculty of Medicine, Cairo University Conclusion: The semiquantitative analysis method including the Tmax and clearance fraction parameters would enable objective assessment of salivary gland function and provide a reproducible means for moderate term follow-up after radioiodine therapy especially those who received total doses more than 150mCi and should be closely monitored for their salivary and lacrimal function after radioiodine therapy.