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Objective: Initial treatment options for Graves' disease include antithyroid drugs, radioactive iodine (RAI), and surgery. Because of similar effects of three modalities, initial treatment preferences differ by country to country. In Korea, iodine-replete area, RAI was used as a second-line option. For these reasons, the RAI success rate in Korea might differ from other countries., Methods: A total of 247 patients were enrolled. The primary outcome was cumulative success rate in the first year, and the secondary outcome was factors that affected the success. Delayed response, which included patients who attained successful RAI during the follow-up, after the first year without further RAI, and factors that affected the delayed response were reviewed., Results: The cumulative success rate in the first year was 62.8%. Higher RAI activity [odds ratio (OR) 2.56, P = 0.02], longer disease duration (OR 0.43, P = 0.01), larger goiter (OR 0.31, P = 0.01), and higher post-RAI fT4 (fT4 between upper normal limit (UNL) to 1.5 × UNL; OR 0.24; P < 0.01, 1.5 × UNL<; OR 0.08; P < 0.01) were associated with RAI success. Twenty-seven patients showed delayed response, and goiter size (P < 0.05), pre-RAI TSH receptor Ab (TRAb) level (P < 0.01) and post-RAI fT4 (P < 0.01) were associated., Conclusion: The success rate of the first RAI in Korea was lower than that in other countries. Delayed response was observed in patients with smaller goiter, low pre-RAI TRAb, and low post-RAI fT4. In these patients, clinical follow-up with monitoring could be an option, and decision of optimal timing of first RAI is crucial.

Aim: The use of radioiodine therapy is common in the treatment of benign thyroid disease. Council directive Euratom 97/43 requires that for all medical exposure of individuals for radiotherapeutic purposes exposures of target volumes should be individually planned. There are several strategies to accomplish this aim for radioiodine therapy including individual radioiodine uptake measurement and using either individual or mean effective radioiodine uptake and half-life. Although it is always simple to use standard activities, the effective thyroidal half-life and thyroidal uptake of I needs to be estimated individually to achieve optimal dosimetric results. We analyzed the radioiodine half-life and uptake in a large number of patients for use in a semi-individual calculation., Methods: Patients presenting consecutively between 1 January 2006 and 31 December 2007 were included in the study. Inclusion criteria were the control of hyperthyroidism and withdrawal of antithyroid drugs 2 days before preliminary radioiodine testing and therapy. Patients were treated for Graves' disease (n=363), nontoxic goitre (n=50), toxic goitre (n=639), or toxic uninodular adenoma (n=365). The effective half-life and uptake of I were estimated by uptake measurements after 24 h and 5 days during the preliminary radioiodine test, and serial measurements over 5 days during therapy., Results: The mean effective half-life of I measured during radioiodine therapy was 5.4 days in Graves' disease, 6.4 days in nontoxic goitre, 6.6 days in toxic goitre, and 5.7 days in toxic uninodular adenoma. The mean maximal uptake of I measured during radioiodine therapy was 64% in Graves' disease, 42% in nontoxic goitre, 38% in toxic goitre, and 31% in toxic uninodular adenoma., Conclusion: These actual values analyzed here might be used for a semi-individual calculation of therapeutic activity when an individual approach is not possible.

Objective: To evaluate the effect of radioiodine therapy for volume reduction in large goitres., Methods: A retrospective study was performed involving 88 patients treated between 2001 and 2007 with radioiodine for toxic or nontoxic goitres. The goitres were between 80 and 250 ml in volume (median 127 ml+/-38.57). Activities of I to be administered were calculated individually through radioiodine testing with uptake measurements over 5 days, the mean activity being 1721+/-440 MBq I (714-2395 MBq I), equivalent to a mean of 14+/-4.19 MBq I/g of thyroid tissue (6-24 MBq I/g of thyroid tissue). The designated dose was 150 Gy for the entire thyroid volume, and post-therapeutic dosimetry revealed a mean thyroid dose of 175+/-45.92 Gy (64-300 Gy). Control examinations were performed, including thyroid blood testing and thyroid ultrasound at 6 weeks and at 3, 6, 12, 24, 36, 48 and 72 months after radioiodine therapy., Results: The mean volume reduction was 41.9% after 3 months and 65.9% after 1 year. Thyroid volume reduction was highly significant (P<0.001) in the first year after radioiodine therapy. No volume increase was observed in any patient during follow-up. Unfortunately, many patients were lost during follow-up (n = 84 after 3 months, n = 38 after 1 year)., Conclusion: Radioiodine therapy is an effective treatment for both nontoxic and toxic goitres, resulting in a highly significant thyroid volume reduction of nearly 66% within 1 year.

Objective: To evaluate the efficacy of radioiodine therapy using I in a group of patients with large multinodular goitre (LMG)., Methods: The study was carried out in patients with goitre volume greater than 100 cm and in patients with LMG who were disqualified from surgery. The study included 34 female participants (age range: 62-84 years) with LMG: 26 patients were hyperthyroid and eight patients had a nontoxic goitre. The patients were treated with 800 MBq of radioiodine administered four times at 3-month intervals (total activity of 3.2 GBq). Before each therapy course, serum thyrotropin, free thyroxin, free triiodothyronine and antithyroid antibodies were measured, ultrasonography and thyroid scan were performed. Patients were followed up for a minimum of 24 months. Fine-needle biopsy was done before qualification to the study., Results: Before therapy, median thyroid volume was 145 cm. It decreased during therapy to 65-76 cm after 12 months and to 50-62 cm after 24 months. After 24 months, 60% of patients were euthyroid and 40% of patients were hypothyroid. During therapy, significant increases in TSHRAb, TPOAb and TgAb levels were observed. No correlation between the levels of antithyroid antibodies, radioiodine uptake, reduction of goitre volume and hormonal status was found., Conclusion: In most cases of LMG, repeated administration of radioiodine is safe and effective. The highest response of the thyroid volume is observed after the first course of treatment. On account of a high incidence of hypothyroidism, the patients should be monitored during and after therapy.

Objective: To evaluate the effect of dose rate on the therapeutic success of radioiodine therapy (RIT) by retrospective analysis of two groups of patients with different dose rates during RIT., Methods: The average dose rate until deposition of 50% of the total radiation dose achieved (the DL50 value) was calculated. Ninety patients with autonomy of the thyroid receiving radiation doses between 300 and 400 Gy were separated in groups with high DL50 values (the DL50 H group) and low DL50 values (the DL50L group). Before and 4 months after RIT free triiodothyronine (FT3), free thyroxine (FT4), basal thyroid stimulating hormone (TSHB), stimulated TSH (TSHS), thyroidal technetium uptake (TcTU), and the existence of focal abnormalities in thyroid scintigraphy were evaluated., Results: The DL50 H and DL50L groups showed no differences before RIT in the parameters assessed as well as in total achieved dose and autonomous thyroid volume. After therapy a significant difference was found in TSHB with higher values in DL50 H (1.89+/-1.49 vs. 1.31+/-1.48 mU . l, P<0.05), FT4 showed a trend to lower values (13.8+/-4.0 vs. 16.1+/-6.2 pmol . l, P=0.09)., Conclusion: The DL50 value has an influence on therapeutic success of RIT. This influence is only discrete and not likely to produce clinically relevant effects in the practical use of RIT.

The aim of this study was to investigate the equivalence in outcome of standardized versus uptake-adjusted dosing of radioactive iodine (131I) for hyperthyroidism. We performed a 1-year follow-up study of two patient cohorts: 326 patients referred for 131I treatment of hyperthyroidism in Graves' disease (GD; n=216) or toxic multinodular goitre (TMG; n=110) in the period June 1995 to January 1998. Of these patients 128 were treated according to a standardized regimen, based on palpated thyroid volume and diagnosis, and 198 with a 131I uptake-adjusted dosimetric method. The incidence of hypothyroidism, euthyroidism or recurrence of disease was recorded. In Graves' disease hypothyroid outcome in the standardized versus adjusted method was 40.7% vs 44.6% (95% CI difference, -17.4 to +9.5%); it was 67.4% vs 70.8% (95% CI difference -15.9 to +9.3%) for all non-euthyroid outcomes. In TMG, due to wide confidence interval ranges a conclusion of equivalence could be made only for recurrence of hyperthyroidism (mean -3.2%, 95% CI, -13.8 to +7.5%). A simplified dosage method for 131I treatment of hyperthyroidism, which omits 131I uptake adjustment, may improve procedure efficiency and patient convenience, and leads to an equivalent outcome in GD and probable equivalent outcome in TMG.