Radioiodine therapy for Plummer's disease based on the thyroid uptake of technetium-99m pertechnetate

The aim of this retrospective study was the evaluation of a TcTUs (global technetium-99m pertechnetate thyroid uptake under suppression)-based approach in 370 patients with thyroid autonomy (Plummer's disease) treated by radioiodine therapy (RIT) under standardised conditions. The analysis included 370 patients (309 females, 61 males; mean age 64+/-11.6 years) treated for thyroid autonomy [unifocal (UFA), 36.8%; multifocal (MFA), 55.7%; disseminated (DISA), 7.6%]. During RIT all patients were under thyroid suppression (TSH< 0.1 microU/ml) and without thionamide treatment. Of the 370 patients, 73% (n=271) were manifestly hyperthyroid and 27% (n=99) subclinically hyperthyroid. A dosimetric study included uptake measurements 24, 48, and 96 h p.i. For dose estimation the Marinelli algorithm was used. For retrospective definition of the target volume we used the equation: Autonomous volume = TcTUs x 5. The spectrum of doses given in our patients ranged from 81 to 1933 Gy. After 18 months of follow-up, RIT was successful (TSH>0.5 microqU/l and/or TcTUs<1.6%) in 310 patients (84%). Of these patients, 291 (94%) were euthyroid (with or without L-thyroxine) and 19 (6%) subclinically hypothyroid (TSH>4 microU/ml). A dose of 350-450 Gy to the autonomous tissue resulted in a success rate of 97% in the UFA group and 81% in the MFA/DISA group. Decrease in total thyroid volume and TcTUs did not differ significantly between successfully treated patients and patients with persistent autonomy. Multivariate analysis of all 370 patients identified four independent factors that negatively influenced the therapeutic success: high pretherapeutic thyroid volume (P=0.0001; odds ratio: 1.017), high pretherapeutic TcTUs values (P=0.0001; odds ratio: 1.378), multifocal/disseminated autonomy (P=0.0056; odds ratio: 3.245) and low target dose (P=0.017; odds ratio: 0.997). It is concluded that the high success rate in the treatment of UFA indicates the concept of TcTUs-based RIT to be valid, but that in the therapy of MFA/DISA the target dose has to be corrected if the total thyroid volume exceeds a critical threshold.