Evaluation of ablation of thyroid remnants with 1850 MBq iodine-131 in 67 patients with thyroid cancer.

Abstract

Radioiodine remnant ablation (RRA) is used to destroy residual normal thyroid tissue after total thyroidectomy in differentiated thyroid carcinoma (DTC) patients. As 1850-MBq RRA is routinely performed at our facility, we evaluated the outcomes. Sixty-seven DTC patients without macroscopic residual lesions after total thyroidectomy were evaluated. Thyroglobulin (Tg) was measured 2-3 months before RRA with thyroxin administration (pretreatment); just before ablation after a 3-week iodine intake restriction with thyroxin withdrawal (THW) (N.=16) or recombinant human thyroid-stimulating hormone (rhTSH) stimulation (N.=51); and 3 months after RRA, after a 2-week iodine intake restriction and 3-week THW (N.=57) or rhTSH stimulation (N.=10). All patients received 131I (1850 MBq) treatment followed by 131I scintigraphy about 8 days later (8.18±0.91) and 131I scintigraphy (185 MBq) after the dosage 24 hours later 3months after RRA. Initial RRA goal was defined as negatively visible uptake in 131I thyroid bed (VUT) and a Tg level of <2 ng/mL 3 months after RRA. Rest 60 patients whose TSH levels were below 0.5 µIU/mL of all 67 patients were evaluated. Negatively VUT on 3 months after RRA was shown in 56 out of 60 patients (93.3%). Initial RRA goal was achieved in 21 (42.0%) of 50 patients, excluding 3 patients whose Tg levels 3 months after RRA were not measured and 7 patients with anti-Tg antibodies. Pretreatment Tg levels (P=0.0003) was significant predictive factor for Initial RRA goal on multivariate logistic regression analysis. RRA with 1850 MBq is effective by visual diagnosis, about 40% of all intermediate or high-risk DTC patients achieved initial RRA goals by both visual and Tg levels diagnosis.