Fixed dosage of I-131 for remnant ablation in patients with differentiatedthyroid carcinoma without pre-ablative diagnostic I-131 scintigraphy

Differentiated thyroid cancer is treated by (near) total thyroidectomy foll owed by radioiodine (I-131) ablation of the residual active tissue in the t hyroid bed. Controversy remains concerning the use and the dose of pre-abla tive diagnostic I-131 scintigraphy. This study was designed to assess the e fficacy of thyroid ablation by high-dose I-131 without pre-ablative diagnos tic I-131 scintigraphy. Ninety-three patients were treated with (near) tota l thyroidectomy and with a high ablative dose of I-131 (3700-7400 MBq). A p reablative I-131 diagnostic scintigram was not performed. To assess the eff icacy of the treatment, all patients were studied with a diagnostic I-131 s cintigram and with thyroglobulin plasma assays 1 year later after withdrawa l of L-thyroxine for 4-6 weeks. The main criterion for a successful ablatio n was the absence of thyroid bed activity. An additional criterion was a th yroglobulin value of <10 mu g.l(-1). Successful ablation according to the m ain criterion was obtained in 88% of patients. Forty patients (43%) showed no neck uptake and had undetectable serum thyroglobulin. Twenty-two patient s (25%) had serum thyroglobulin concentrations between 1 and 10 mu g.l(-1). Twenty-six patients (27%) had thyroglobulin >10 mu g.l(-1), 19 patients sh owing residual thyroid uptake or metastatic lesions. We conclude that high- dose radioiodine ablation without prior diagnostic scintigraphy results in a high rate of successful ablation, preventing I-131 treatment. ((C) 2000 L ippincott Williams & Wilkins).