PT  - JOURNAL ARTICLE
AU  - Zanzonico, Pat B.
AU  - Becker, David V.
AU  - Hurley, James R.
TI  - Enhancement of Radioiodine Treatment of Small-Pool Hyperthyroidism with Antithyroid Drugs: Kinetics and Dosimetry
DP  - 2004 Dec 01
TA  - Journal of Nuclear Medicine
PG  - 2102--2108
VI  - 45
IP  - 12
4099  - http://jnm.snmjournals.org/content/45/12/2102.short
4100  - http://jnm.snmjournals.org/content/45/12/2102.full
SO  - J Nucl Med2004 Dec 01; 45
AB  - 131I-Iodide is the treatment of choice in most cases of hyperthyroidism, with a standard 7,000-cGy (rad) thyroid absorbed dose generally resulting in an incidental blood absorbed dose of less than 10 cGy (rad). However, in ∼15% of patients there is a small, rapidly secreted thyroid iodine pool (small-pool patients) and, based on theoretic calculations, an incidental blood absorbed dose of up to 150 cGy (rad) could result. In such small-pool patients, continuing antithyroid drugs (ATDs) at a reduced dosage during 131I therapy should inhibit the formation of 131I-labeled levothyroxine and triiodothyronine and thereby reduce the protein-bound 131I-iodine concentration in blood and the blood absorbed dose. Methods: To test this hypothesis, thyroid and blood time–activity data were measured and absorbed doses were calculated for an 131I tracer administered to small-pool hyperthyroid patients (n = 9) not receiving ATDs (off ATDs) and then receiving ATDs (on ATDs). Results: The blood absorbed dose (cGy/37 MBq [rad/mCi] administered) was reduced from 2.54 ± 0.91 (mean ± SD) without ATDs to 1.27 ± 0.54 with ATDs (P < 0.0001), whereas the thyroid absorbed dose was unchanged (1,870 ± 700 vs. 2,080 ± 1,080). The blood absorbed dose for an administered 131I activity required to deliver a standard prescribed absorbed dose of 7,000 cGy (rad) to the thyroid therefore was reduced by over 50% with ATDs, from 11.3 ± 6.5 to 4.9 ± 2.8 cGy (rad) (P < 0.001). Conclusion: Continued administration of ATDs during 131I therapy thus can effectively reduce extrathyroid radiation in small-pool patients without significantly reducing the target tissue (i.e., thyroid) dose.