Total-body scintigraphy with thallium-201 and iodine-131 in the follow-up of differentiated thyroid cancer.

UNLABELLED: We analyzed the significance of total body scintigraphy with 201Tl in the follow-up of patients with differentiated thyroid cancer, both in the preablation and ablated stages.

METHODS: Prospective assessment was 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 131I follow-up scan after 131I ablation therapy. Each study consisted of a 201Tl scan performed while the patient was receiving thyroid hormone therapy, an 131I scan performed when endogenous thyroid-stimulating hormone levels were higher than 50 mlU/ml and determination of thyroglobulin (Tg) concentration using the same sample.

RESULTS: In the 115 scans in the preablation group, the findings for 201Tl and 131I agreed in 26 scans and disagreed in 89 scans. In 59 discordant studies, only 131I detected focal accumulation, and, in 54 of these, Tg levels were undetectable. Of the other 30 discordant studies, 201Tl and 131I detected focal uptake in 27 studies, although they did not reveal the same lesions, and in 3 studies, only 201Tl detected focal accumulation; in these 30 studies, the association of detectable Tg predominated. Of the 63 studies in the ablated group, the results agreed for the two tracers in 49 and disagreed in 14 studies. In 13 of the 14 discordant studies, 201Tl detected focal uptake, and, in 10 of these, Tg was detectable. Thus, 31 of the 116 patients assessed (15 preablation and 16 ablated) had at least one lesion that was detected by 201Tl but not detected by 131I. A definitive diagnosis could be established in 26 patients, and the presence of thyroid cancer was confirmed in 23. The sensitivity and specificity in the ablated group were 94% and 96%, respectively, for 201Tl and 29% and 100%, respectively, for 131I.

CONCLUSION: The high sensitivity of 201Tl scintigraphy in detecting tumor tissue indicates that the inclusion of this technique in the follow-up of patients with differentiated thyroid carcinoma should be considered in both the preablation and the ablated stages.