REDUCTION IN THYROID VOLUME AFTER RADIOIODINE THERAPY OF GRAVES HYPERTHYROIDISM - RESULTS OF A PROSPECTIVE, RANDOMIZED, MULTICENTER STUDY

The reduction in thyroid size in 92 patients treated with radioiodine for Graves' thyrotoxicosis was monitored by ultrasound volumetry. The patients were randomly treated with either a standard I-131 activity o f 555 MBq or an activity calculated to deliver a thyroid dose of 100 G y. Within 1 year after radioiodine treatment, a remarkable volume redu ction of about 71% (median) (quantile 25% (Q 25) = 49%, Q 75 = 82%, n = 67) was observed. The bulk of this reduction (median 57%, Q 25 = 21% , Q 75 = 74%, n = 92) was found within the first 6 months. Statistical analysis reveals that the effect was clearly related to the thyroid d ose actually achieved during therapy. The median reduction obtained 6 months after radioiodine application was 45% for <100 Gy, 56% for 100- 200 Gy and 67% for >200 Gy (n = 28, 39, 25 respectively). Twelve month s after radioiodine application, the effect became less evident: 53%, 68% and 75% respectively (n = 17, 29, 21). The higher median thyroid d ose actually achieved by standard than by calculated activity (215 Gy vs. 116 Gy) explains the more pronounced volume reduction in the stand ard group than in the calculated group: 60% vs. 47% 6 months (n = 47, 45) after radioiodine treatments and 74% vs. 66% 12 months (n = 31, 36 ) after radioiodine application, The relative reduction in thyroid siz e was just as marked in patients with large thyroids as in those with small glands. The goitre prevalence (thyroid volume > 20 mt in women a nd > 25 mL in men) was reduced from 73% to only 16% 1 year after radio iodine treatment. In patients with a thyroid volume of more than 60 mL , the median pretherapeutic thyroid volume of 102 mL was reduced to 29 mL. In conclusion, radioiodine treatment in Graves' hyperthyroidism s ufficiently reduces thyroid volume in a dose-dependent manner. The fin dings of this study demonstrate that radioiodine is also an attractive mode of therapy for Graves' patients with substantial thyroid enlarge ment.