TOTAL-BODY SCINTIGRAPHY WITH TL-201 AND I-131 IN THE FOLLOW-UP OF DIFFERENTIATED THYROID-CANCER

We analyzed the significance of total body scintigraphy with Tl-201 in the follow-up of patients with differentiated thyroid cancer, both in the preablation and ablated stages. Methods: Prospective assessment w as performed in 116 patients who were involved in 178 studies (115 in preablation and 63 after ablation). For ablation, an absence of uptake in the thyroid bed was required in the total I-131 follow-up scan aft er I-131 ablation therapy. Each study consisted of a Tl-201 scan perfo rmed while the patient was receiving thyroid hormone therapy, an I-131 scan performed when endogenous thyroid-stimulating hormone levels wer e higher than 50 mlU/ml and determination of thyroglobulin (Tg) concen tration using the same sample. Results: In the 115 scans in the preabl ation group, the findings for Tl-201 and I-131 agreed in 26 scans and disagreed in 89 scans. In 59 discordant studies, only I-131 detected f ocal accumulation, and, in 54 of these, Tg levels were undetectable. O f the other 30 discordant studies, Tl-201 and I-131 detected focal upt ake in 27 studies, although they did not reveal the same lesions, and in 3 studies, only Tl-201 detected focal accumulation; in these 30 stu dies, the association of detectable Tg predominated. Of the 63 studies in the ablated group, the results agreed for the two tracers in 49 an d disagreed in 14 studies. In 13 of the 14 discordant studies, Tl-201 detected focal uptake, and, in 10 of these, Tg was detectable. Thus, 3 1 of the 116 patients assessed (15 preablation and 16 ablated) had at least one lesion that was detected by Tl-201 but not detected by I-131 . A definitive diagnosis could be established in 26 patients, and the presence of thyroid cancer was confirmed in 23. The sensitivity and sp ecificity in the ablated group were 94% and 96%, respectively, for Tl- 201 and 29% and 100%, respectively, for I-131. Conclusion: The high se nsitivity of Tl-201 scintigraphy in detecting tumor tissue indicates t hat the inclusion of this technique in the follow-up of patients with differentiated thyroid carcinoma should be considered in both the prea blation and the ablated stages.