Radioiodine Treatment of Plummer and Multinodular Toxic and Nontoxic Goiter Disease by the First Approximation Dosimetry Method

The aim of this study was to assess the efficacy of mean radioiodine activities of 12.6 MBq/mL in order to achieve a successful treatment of hyperthyroidism with a single radioiodine dose and a low incidence of hypothyroidism. We evaluated 51 patients with Plummer disease, 41 patients with multinodular toxic goiter, and 9 patients with compressive toxic and nontoxic goiter, after a short suspension of antithyroid drugs, with the exclusion of patients with critical cardiovascular conditions, an expanded iodine pool, and a nodular volume larger than 120 mL. Target volume was measured by ultrasonography and calculated by the ellipsoid method. All the patients underwent a thyroid uptake test with 1.85 MBq of ¹³¹I and measurements on the neck and thigh at 2, 6, and 24 hours. Target volume was 21.5 ± 21.4 mL for group 1, 15.4 ± 10.7 mL for group 2, and 56.4 ± 12.8 mL for group 3. The 24 hours uptake (mean % ± standard deviation) was 43.1 ± 19.9, 48.5 ± 15.4, 56.4 ± 12.8, respectively, for groups 1, 2 and 3. Mean follow-up was group 1: 23 ± 17 months; group 2: 23 ± 14 months; and group 3: 28 ± 20 months. First approximation dosimetry took into account thyroid volume and the 24-hour uptake percentage. A euthyroidism condition was reached in 40 of 51 patients (78.4%) of group 1, 35 of 41 patients (85.4%) of group 2, and 6 of 9 patients (66.7%) of group 3. Hypothyroidism was observed in 13 of 101 patients (12.9%). Only 9 of 101 (8.9%) patients were subclinically hyperthyroid at the end of follow-up. The over-all efficacy of treatment was 91.1%. Reduction (%) of nodule volume was 66 ± 23, 57 ± 18, and 79 ± 13, respectively, in groups 1, 2, and 3, with scintigraphic disappearance of hot nodules or persistence of cold nodules with the recovery of extranodular thyroid tissue in 76 patients.