Required therapeutic dose of ¹³¹I for thyroid ablation after surgery for differentiated thyroid carcinoma

Full text of publication follows. After operation for carcinoma of the thyroid gland a lot of patients are treated with radioactive iodine for ablation of the residual thyroid parenchyma. Aim: to determine the appropriate dose of radioactive iodine for ablation of the residual thyroid parenchyma in patients operated for differentiated thyroid carcinoma. Materials and methods: the study includes 316 patients who underwent a whole-body scan (WBS) scintigraphy with ¹³¹I. From 2009 to 2012 year 632 images were taken. Patients range from 21 to 78 years old. The scan was performed on a dual-headed gamma camera Siemens after an oral reception of a diagnostic dose ¹³¹I (2 mCi). The remnants of thyroid parenchyma were registered in 67 of the patients. 39 patients with registered remnants of thyroid parenchyma and slightly elevated thyroglobulin (TG) values who took therapeutic dose ¹³¹I (80-100 mCi) underwent a WBS scintigraphy with ¹³¹I and did not display remnants of thyroid parenchyma or extra thyroid accumulation of the radio nucleotide. 23 patients with several remnants of thyroid parenchyma and elevated values of TG who underwent a WBS scintigraphy with ¹³¹I eight to ten months after reception of the first dose therapeutic iodine (80-100 mCi) displayed persisting remnants of thyroid parenchyma. They were treated with a second dose of ¹³¹I (50-100 mCi). In 5 patients with high values of TG besides the thyroid remnants 3 of the patients displayed an extra thyroid accumulation in the lungs and 2 of them displayed an extra-thyroid fixation in the thoracic vertebras in addition to the fixation in the lungs. These 5 patients were treated twice with ¹³¹I, but still displayed the remnants of thyroid parenchyma and extra thyroid fixation. That group was treated with a third dose of ¹³¹I (30-50 mCi) and no remnants of thyroid parenchyma and extra-thyroid fixation of the radio nucleotide were visualized on the control WBS scintigraphy. Conclusion: in the majority of the patients with thyroid remnants after surgery for differentiated thyroid carcinoma one dose of therapeutic ¹³¹I of 80-100 mCi is enough for ablation of the thyroid remnants. The requirement of a second dose of therapeutic ¹³¹I is evaluated by a thorough assessment of the thyroglobulin values. (authors)