Harold L. Atkins 94 Table 6-2 Calculated Radiation Dose to the Thyroid From '*I (1 mCi in a 20-g Gland) Initial Dose Rate (rads/day) Author Whole Gland Harperet al.5? 36.8 Gavron and Feige*! 78 Lewitus et al.** Ben-Porath et al.** MIRDt 88.8 Gillespie et al.*9 Reddy et al.*° 75 72 Colloid-Cell Interface 170 457 63.6 151.2 77.8 Nucleus 46 112 Total Dose (rads)* Whole Gland 795 1620 32.4 1685 37.2 25.9 1918 Colloid-Cell Interface Nucleus 3672 9871 994 2419 3266 1680 804 559 1374 700 1555 *Assumes T% eff. of 115 days. +Author’s calculation using MIRDtables for absorbed dose per unit cumulated activity.*° Several clinical trials of '°I for hyperthyroidism were initiated in the hope that late hypothyroidism could be substantially reduced (Table 6-3). These have varied in the dose of '*1 used relative to the conventional'*'I dose and the results have been mixed. At least two groups have discontinued their study because of lack of improvement in results. In Glasgow the initial trial used a dose in millicuries of '**] four times the usual dose of '*4I. This resulted in a rapid reversal of the hyperthyroid state but with a substantial percentage of ensuing hypothyroidism. With reduction in the amount of '=] administered the incidence of hypothyroidism decreased, but with an increase tn persistent hyperthyroidism.®* On the other hand, Israeli investigators have used fewer millicuries of '*1 than of '*'I, assuming a quality factor of 3 for the rad dose in the apical region of the cell from the low-energy Auger electrons.® The relapse rate was high leading to the use of increased doses andfinally to a combination of !*1 and "I in equal millicurie amounts.®* With this combined therapyit was felt that a rapid response by affecting hormonogenesis wasinitiated by **5I and that long-term effects were maintained by the cell killing action of '"I. This combination led to the lowest incidence of recurrence but without much effect on the incidence of hypothyroidism. A series of patients treated by Siemsen etal.®’ initially showed a low rate of hypothyroidism but with a high rate of persistent hyperthyroidism. No further patients are being addedto this study because of the conclusion that the results were nobetter than with '*!I. The series of Werneretal.®* and that of Weidingeret al.’ continue, and a recent study by Glanzmann and Horst” shows promising results. In this last study there was no hypothyroidism at 18 to 24 months and 18 percent persistent hyperthyroidism. Of those patients with persistent or relapse of thyrotoxicosis, more than 30 percent had T; thyrotoxicosis. Another small series of patients was treated withI by Gimlette and Hoschl.”! The dose of !41 was identical to the dose of }7I used in a control group.