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Thyroid remnant ablation in patients with papillary cancer: a comparison of low, moderate, and high activities of radioiodine.

Kusacic Kuna S, Samardzic T, Tesic V, Medvedec M, Kuna K, Bracic I, Despot M, Dodig D

Clinical Department of Nuclear Medicine and Radiation Protection, Clinical Hospital Centre Zagreb, Zagreb, Croatia. sanja.kusacickuna@gmail.com

OBJECTIVE: The consensus about optimal activities of I-131 for thyroid remnant ablation has not yet been achieved. The aim of this study was to compare ablation rates obtained with different I-131 activities. PATIENTS AND METHODS: The study included 466 patients divided into four groups according to I-131 activities given after total thyroidectomy for papillary thyroid cancer: group A [168 patients who received 888 MBq (24 mCi)], group B [125 patients who received 1480 MBq (40 mCi)], group C [65 patients who received 1850 MBq (50 mCi)], and group D [108 patients who received 4440 MBq (120 mCi)]. Ablation outcome was assessed by whole-body scan in hypothyroid state 6-9 months after ablation and finally 18-21 months after the treatment. RESULTS: The rate of successful ablation was similar in the group of patients who received 24 and 40 mCi (75 and 71.2%, respectively). The higher rate of ablation was achieved in the groups treated with 50 and 120 mCi of radioiodine (87.69 and 90.74%, respectively). The ablation rates at the first follow-up examinations (59.5, 67.2, 73.9, 80.6%) were lower than at second control study (75.0, 71.2, 87.7, 90.7%) in all groups. Time required for thyroid remnant ablation seems to be >or=18 months. CONCLUSION: Our study indicates that activity of 50 mCi seems to be optimal to achieve a successful ablation rate (approximately 90%). Low I-131 activities are acceptable for lower risk patients because of satisfactory ablation rate (>70%), lower expense, and minimal radiation burden to patients as well as lower radiation exposure to clinical staff. The ablative use of high activities seems neither justified nor optimized.

Published 9 April 2009 in Nucl Med Commun, 30(4): 263-9.
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