TL-201 SCINTIGRAPHY IN DIFFERENTIATED THYROID-CANCER - COMPARISON WITH RADIOIODINE SCINTIGRAPHY AND SERUM THYROGLOBULIN DETERMINATIONS

The role of thallium-201 (Tl-201) scintigraphy in the followup evaluation of differentiated thyroid carcinoma (DTC) is controversial. Desirable characteristics of Tl-201 scintigraphy including the potential for no thyroid hormone withdrawal, immediate imaging postinjection, and low radiation burden relative to iodine-131 (I-131) suggests it is logistically superior to I-131 scintigraphy. Fifty-two patients with DTC were evaluated with Tl-201 and I-131 neck and chest images, and serum thyroglobulin measurements. In post-thyroidectomy and pre-I-131 ablation therapy patients, very little Tl-201 accumulation was noted within the thyroid bed, with discordantly increased I-131 activity and normal serum thyroglobulin measurements. Twenty-nine percent of patients evaluated after I-131 ablative therapy had elevated serum thyroglobulin levels and localized neck and chest abnormalities on Tl-201 scan that were not seen on I-131 studies. Our data suggest that Tl-201 is more sensitive than I-131 diagnostic (5 mCi) studies for detection of DTC, while I-131 is more sensitive in detecting normal residual thyroid tissue postoperatively.