Iodine biokinetics and radioiodine exposure after recombinant human thyrotropin-assisted remnant ablation in comparison with thyroid hormone withdrawal.

CONTEXT: A few prospective studies have evaluated the use of recombinant human TSH (rhTSH) for radioiodine remnant ablation. OBJECTIVE: Our objective was to compare the effects of the both TSH regimens on iodine biokinetics in the thyroid remnant, dosimetry, and radiation protection. DESIGN: We conducted a prospective randomized study. MATERIALS AND METHODS: Eighty-eight patients were enrolled for radioiodine ablation to either the hypothyroid or rhTSH arms. A whole-body scan was performed at 48 and 144 h after therapy. Dose rates were assessed at 24, 48, and 144 h. Urinary samples were obtained during the first 48 h. Thyroglobulin was assessed before and after therapy. Iodine biokinetics in the remnants were calculated from gamma-count rates. Radiation-absorbed dose was calculated using OLINDA software. Exposure estimation was based on a validated model. RESULTS: The effective half-life in the remnant thyroid tissue was significantly longer after rhTSH than during hypothyroidism (P = 0.01), whereas 48-h (131)I uptakes and residence times were similar. After therapy, thyroglobulin release (a marker of cell damage) was lower in the rhTSH arm. The mean total-body effective half-life and residence time were shorter in patients treated after rhTSH. Residence time was also lower for the colon and stomach. Absorbed dose estimates were lower in the rhTSH arm for the lower large intestine, breasts, ovaries, and the bone marrow. Dose rates at the time of discharge were lower in the rhTSH group with a reduction in cumulative radiation exposure to contact persons. CONCLUSIONS: In comparison with thyroid hormone withdrawal, rhTSH is associated with longer remnant half-life of radioactive iodine while also reducing radiation exposure to the rest of the body and also to the general public who come in contact with such patients.