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

Differentiated thyroid cancer is treated by (near) total thyroidectomy followed by radioiodine (I-131) ablation of the residual active tissue in the thyroid bed. Controversy remains concerning the use and the dose of pre-ablative diagnostic I-131 scintigraphy. This study was designed to assess the efficacy of thyroid ablation by high-dose I-131 without pre-ablative diagnostic I-131 scintigraphy. Ninety-three patients were treated with (near) total thyroidectomy and with a high ablative dose of I-131 (3700-7400 MBq). A preablative I-131 diagnostic scintigram was not performed. To assess the efficacy of the treatment, all patients were studied with a diagnostic I-131 scintigram and with thyroglobulin plasma assays 1 year later after withdrawal of L-thyroxine for 4-6 weeks. The main criterion for a successful ablation was the absence of thyroid bed activity. An additional criterion was a thyroglobulin value of <10 mu g.l(-1). Successful ablation according to the main criterion was obtained in 88% of patients. Forty patients (43%) showed no neck uptake and had undetectable serum thyroglobulin. Twenty-two patients (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 showing 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 Lippincott Williams & Wilkins).