RECOMMENDATION 35Pretherapy scans a

RECOMMENDATION 35Pretherapy scans and=or measurement of thyroid bed uptake may be useful when the extent of the thyroid remnantcannot be accurately ascertained from the surgical reportor neck ultrasonography, or when the results would altereither the decision to treat or the activity of RAI that isadministered. If performed, pretherapy scans should utilize 123I (1.5–3 mCi) or low-activity 131I (1–3 mCi), with thetherapeutic activity optimally administered within 72hours of the diagnostic activity. Recommendation rating: C[B18] What activity of 131I should be used for remnantablation? Successful remnant ablation is usually defined asan absence of visible RAI uptake on a subsequent diagnosticRAI scan or an undetectable stimulated serum Tg. Activitiesbetween 30 and 100 mCi of 131I generally show similar rates ofsuccessful remnant ablation (251–254) and recurrence rates(213). Although there is a trend toward higher ablation rateswith higher activities (255,256), a recent prospective randomized study found no significant difference in the remnantablation rate using 30 or 100 mCi of 131I (257). Furthermore,there are data showing that 30 mCi is effective in ablating theremnant with rhTSH preparation (258). In pediatric patients,it is preferable to adjust the ablation activity according to thepatient’s body weight (259) or surface area (260).& RECOMMENDATION 36The minimum activity (30–100 mCi) necessary to achievesuccessful remnant ablation should be utilized, particularlyfor low-risk patients. Recommendation rating: B& RECOMMENDATION 37If residual microscopic disease is suspected or documented,or if there is a more aggressive tumor histology (e.g., tallcell, insular, columnar cell carcinoma), then higher activities (100–200 mCi) may be appropriate. Recommendationrating: C[B19] Is a low-iodine diet necessary before remnantablation? The efficacy of radioactive iodine depends on theradiation dose delivered to the thyroid tissue (261). Lowiodine diets (