Value of 201Tl imaging in predicting therapeutic 131I uptake in patients with thyroglobulin positive but 131I scan negative differentiated thyroid cancer

The assessment of patients after surgery and radioiodine therapy commonly includes the use of serum thyroglobulin assay and 131I imaging to identify functioning thyroid remnants and metastases. However, the sensitivity of 131I imaging for this purpose has been shown to be sub optimal, especially in small lesions. Therefore, a significant number of patients presenting with a positive thyroglobulin assay but negative whole body 131I scan create a dilemma in therapeutic management. Other radiopharmaceuticals including 201Tl have been demonstrated to have better sensitivity than 131I. It is not clear however whether 201Tl imaging contributes to the decision-making process for subsequent 131I therapy. The published data is particularly sparse in patients with positive serum thyroglobulin assay but negative whole body 131I scan. This study was therefore conducted to define the clinical role of 201Tl scanning in this subgroup of patients