DOSIMETRIC MEASUREMENTS USING 124-I-PET DURING 131-I THERAPY OF HYPERTHYROIDISM
124-I measurements has been performed in 12 patients with toxic multinodular goiter, 2 with toxic adenoma, and 1 with Graves disease. 131-I therapeutic dosis and 30<196>40 MBq 124-I were administere orally, simultaneously. PET images (10 minutes transmission and 75000 coincidental events in emission phase) were acquired using a whole-body PET-scanner (GE Advance). In each patient, 4<196>5 scans were performed in two weeks, starting 24 hours after application. In all patients scintillation probe measurements of 131-I kinetics were performe simultaneously. Uptake values and effective half-lives of 131-I adn 124-I showed mean deviations of 1.8% and 4 hours, respectively. Correlation coefficient was: 0.99 for uptake and 0.88 for effective half-life. Additional evaluation of regional functionally autonomous and paranodular tissue revealed considerable diference both in 124-I specific uptake (nodules: 12.6<196>29.3 KBq/ml/MBq, rest thyroid tissue: 2.0<196>8.3 KBq/ml/MBq) and in efective half-lives (nodules: 93<196>193 hours, rest thyroid tissue 107<196>162 hours) which concerned different nodules within the same thyroid, as well. Results indicate that 124-I PET enables a precise measurement of the regional radioiodine distribution and kinetics in functionally active thyroid tissue, necessary for the accurate calculation of the target dose to be delivered by radioiodine therapy.