EFFICACY OF LOW-DOSES OF RADIOIODINE IN THE TREATMENT OF AUTONOMOUS THYROID-NODULES - IMPORTANCE OF DOSE AREA RATIO/

Radioiodine (I-131) represents an interesting alternative to surgery i n the treatment of autonomously functioning thyroid nodules (AFTN), bu t leads to a significant incidence of hypothyroidism when high doses a re used. Over 4 years, we have treated 40 patients (hyperthyroid [Plum mer's disease]: 6, single hot nodules with undetectable thyrotropin [T SH] and normal serum free thyroxine [FT4]: 34), 34 single hot nodules with undetectable thyrotropin TSH and normal serum free thyroxine [FT4 ] with I-131. The dose level was neither related to the concentration of FT4 nor to the iodine uptake on thyroid scintigram. Retrospectively we measured the nodule's area on the scan and calculated the dose/are a ratio (DAR). Three months after treatment, 30 patients were euthyroi d, 9 were still hyperthyroid, and 1 was hypothyroid. The mean DAR of t he euthyroid patients was twofold higher than for the hyperthyroid sub jects (1.4 +/- 0.8 vs. 0.7 +/- 0.3 mCi/cm(2); p=.003) and one-half the DAR for the hypothyroid patient (2.82 mCi/cm(2)). Twenty of the 30 eu thyroid patients had received a dose higher than 1 mCi/cm(2) and 7 of 9 hyperthyroid patients had received a dose lower than 1 mCi/cm(2). (c hi(2)=12.9; p=.02). The initial values of T-4, TSH, and dose level of patients who were euthyroid or hyperthyroid at 3 months were not diffe rent. These data suggest that the efficacy of I-131 for treating AFTN depends on the DAR, rather than the initial T-4 value or the I-131 upt ake. A DAR between 1 and 1.5 mCi/cm(2) seems to be optimal and avoids hypothyroidism.