Improved dose concept for radioiodine therapy of multifocal and disseminated functional thyroid autonomy

Abstract

Reinhardt M, Emrich D, Krause T, Bräutigam P, Nitzsche E, Blattmann H, Schümichen C, Moser E. Improved dose concept for radioiodine therapy of multifocal and disseminated functional thyroid autonomy. Eur J Endocrinol 1995;132:550–6. ISSN 0804–4643 The present study analyzes the improvement of the outcome of radioiodine therapy in non-immunogenic hyperthyroidism by adapting the target dose to the 99mTc-pertechnetate thyroid uptake under suppression (TcTUs) prior to radioiodine therapy. The TcTUs is a substitute for the non-suppressible iodine turnover. The 89 patients presented with a basal thyrotropin level of <0.1 mU/l, normal values for free triiodothyronine and thyroxine and with multifocal or disseminated thyroid autonomy. These terms describe the scintigraphic distribution pattern of autonomous iodine turnover. Thirty-two patients had a TcTUs between 1.6 and 3.2% (group A) and 57 had a TcTUs > 3.2% (group B). Fifty-five patients (three of group A and 52 of group B) were treated previously for overt hyperthyroidism with antithyroid drugs. Target doses of 150 and 200 Gy were used in both groups and 300 Gy in group B only. Six months after radioiodine therapy, a basal TSH level of ≥ mU/l as criterion of therapy success was observed in 94% of group A and in 54% of group B. Further differentiation of group B shows an increasing success rate with the target dose used: 45% after 150 Gy, 50% after 200 Gy and 90% after 300 Gy. In patients with a basal TSH level of <0.5 mU/l after radioiodine therapy, the TcTUs was evaluated again. Persistence of functional thyroid autonomy, defined as TcTUs > 1.6%, was found in 89% (one patient of group A, 24 patients of group B) and still observed a high extent of autonomous function in 25% of them, evidenced by a TcTUs > 3.2% (seven patients of group B, target doses of 150 or 200 Gy). No case of overt hypothyroidism was observed within the first 6 months after radioiodine therapy and no difference was found in therapy outcome between multifocal and disseminated thyroid autonomy. As a consequence, the target dose should be adapted to the TcTUs prior to radioiodine therapy in the range of 150–300 Gy to the total thyroid gland. Michael Reinhardt, Abteilung Nuklearmedizin, Radiologische Universitätsklinik, Hugstetter Straße 55. 79106 Freiburg im Breisgau, Germany