Assessing the Contribution of Diagnostic Thyroid Imaging to Radio Active Iodine Treatment in Patients with Diffuse Toxic Goitre (Graves’ Disease)

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Abstract Objectives: The aim of this study was to assess the impact of the prescribed activity of radioiodine (131I ) according to the thyroid uptake function percentage (99mTc uptake) and radioiodine treatment outcomes of Graves’ disease. Methods: A retrospective study of fifty-seven patients with Graves’ disease who underwent a thyroid 99mTc scan prior to radioactive iodine treatment from January 2014 to July 2018 was conducted. A 99mTc- thyroid scan was performed to determine the prescribed activity of 131I. Thyroid imaging was interpreted by an experienced nuclear medicine clinician, and patients were usually diagnosed by endocrinologists. 131I activities were prescribed by an Administration of Radioactive Substances Advisory Committee (ARSAC) holder nuclear medicine clinician. The amount of the prescribed activity correlated with the time of developing hypothyroidism. Results: Patients were divided into four groups according to their uptake function percentage—a 0-5 % group, 6-10% group, 11-15% group, and 16-25% group—given that normal uptake function is 0.4- 4.0%. The Spearman’s correlation coefficients were calculated for the administered activity and the time for developing hypothyroidism. A higher Spearman’s correlation coefficient (-0.800) was noted for the 11-15% group. The other groups had the following Spearman’s correlation coefficients (5-0% group: -0.303; 6-10% group: -0.181; 16-25% group: -0.348). Conclusion: Majority (91%) of the patients developed hypothyroidism or euthyroidism following radioactive iodine treatment. The results indicate that 99mTc thyroid imaging prior to radioactive iodine treatment can be useful. It was specifically found that it can predict the early development of hypothyroidism or euthyroidism in the group of patients with an uptake function between 11-15%. This group was statistically more significant than other groups when the prescribed activity was correlated with 99mTc uptake. However, the 0-5% group and 16-15% group were not significant, with a correlation coefficient -0.3, and the 6-10% group was also not significant, with correlation coefficient -0.18.