RADIOIODINE THERAPY OF GRAVES HYPERTHYROIDISM - STANDARD VS CALCULATED (131)IODINE ACTIVITY - RESULTS FROM A PROSPECTIVE, RANDOMIZED, MULTICENTER STUDY

The present prospective, randomized, multicentre study was performed t o directly compare for the first time the effectiveness of a standard activity of 555 MBq (131)iodine vs. an activity calculated to deliver 100 Gy for treatment of Graves' thyrotoxicosis. Therapeutic success wa s defined as the elimination of hyperthyroidism 6 months after radioio dine application (range 4.5-8 months). A success rate of more than 90% in eliminating hyperthyroidism was reported for both approaches, but only in retrospective investigations. Investigated prospectively, hype rthyroidism was eliminated in only 71% of the patients receiving stand ard activity (70/98) and 58% of those randomized for calculated activi ty (62/107). In the patients with standard activity, therapeutic succe ss was inversely related to thyroid size. The rate was 100% for thyroi d volumes less than or equal to 15 mL, 95% for 16-30 mL, 68% for 31-45 mL, 44% for 46-50 mL, 20% for 61-75 mL and 25% for greater than or eq ual to 75 mL. In those patients with an activity calculated to deliver 100 Gy (except in those with a volume less than or equal to 15 mL) th is size/outcome dependency was almost compensated. The rates were 86%, 65%, 45%, 61%, 41% and 45%, respectively. Furthermore, detailed stati stical analysis revealed a strong correlation between the success of t herapy and the radiation dose actually absorbed by the thyroid. The ra te was 11% for a target dose of 50 Gy, 50% for 100 Gy, 67% for 150 Gy, 80 % for 200 Gy, 84 % for 250 Gy, 88 % for 300 Gy, 90 % for 350 Gy an d 93% for 400 Gy. Based on the results obtained in the present study, we strongly recommend individual calculation of the (131)iodine activi ty to be administered for treatment of Graves' hyperthyroidism. Howeve r, the target dose should be in the range of 200 Gy.