Outpatient Thyroid Remnant Ablation Using Repeated Low 131-Iodine Activities (740 MBq/20 mCi x 2) in Patients with Low-Risk Differentiated Thyroid Cancer. Clerc J, Bienvenu-Perrard M, Pichard de Malleray C, Dagousset F, Delbot T, Dreyfuss M, Groussin L, Marlowe RJ, Leger FA, Chevalier A. J Clin Endocrinol Metab. 2012 Jan 11.
ABSTRACT- In low-risk differentiated thyroid cancer (DTC), postoperative (131)I remnant ablation should employ a minimum effective activity; reports increasingly suggest efficacy of low activities, e.g. 1110 MBq/30 mCi. We retrospectively studied the ablation capability and diagnostic utility of the Minidose protocol, two 740-MBq/20 mCi outpatient administrations, 6-18 months apart, plus related diagnostic procedures, in 160 consecutive (near-) totally thyroidectomized low-risk DTC (pT1/N0-Nx) patients. Successful ablation comprised negative 740-MBq whole-body (20mCi) scintigraphy with cervical uptake below 0.1%, negative stimulated thyroglobulin (STg) (<1 ng/ml, negative thyroglobulin antibodies), and negative Doppler ultrasonography (performed around Minidose 2). Minidose imaging found unsuspected nodal or distant metastases in nine of 160 patients (5.6%). Ablation success rates after one (two) 740-MBq activity (activites) were 75.9% (90.2%) in 145 (132) evaluable imaging-negative patients. Compared with thyroid hormone withdrawal, recombinant human TSH stimulation was associated with more frequent ablation success after the first 740 MBq but success rates no longer differed significantly after both administrations. Patients with STg below 10 ng/ml at Minidose 1 were oftener ablated at Minidose 2 (odds ratio = 13.9, 95% confidence interval = 2.5-76.4, P < 0.003), attaining 92.0% final ablation success, suggesting that one 740-MBq activity should suffice in this subgroup. All 81 evaluable patients with prolonged follow-up (mean 41.8 ± 21.9 months after Minidose 1) had no evidence of disease at the last visit.Conclusions:The Minidose outpatient ablation protocol is effective and diagnostically useful
COMMENT-Further support for the utility of low dose131-I thyroid ablation ( <50mCi), in this instance in low risk patients.