The role of iodine‐131 and thallium‐201 imaging and serum thyroglobulin in the management of differentiated thyroid carcinoma

Background. A prospective study was conducted to evaluate the use of iodine‐131 sodium scintigraphy, thallium‐201 chloride scintigraphy, and quantitative serum thyroglobulin estimation in the detection of differentiated thyroid carcinoma after thyroidectomy and iodine‐131 sodium ablative therapy. Methods. Thirty‐one patients with a median age of 45.6 years (range, 20–73 years) were included in the study. After optimal endogenous thyroid‐stimulating hormone stimulation (> 50 mU/ml), 53 pairs of iodine‐131 and thallium‐201 scans were performed. Concomitant serum thyroglobulin levels were available for 32 pairs of scans. The presence or absence of thyroid cancer was established by clinical, radiologic, and/or biopsy findings. Results. The concordance between iodine‐131 and thallium‐201 scan findings in the presence of disease (25 scan sets) was 36%. The concordance in the absence of disease (28 scan sets) was 82%. Iodine‐131 scanning was found to be significantly better (P < 0.05) than thallium‐201 scanning, in terms of sensitivity (0.8 versus 0.6), specificity (0.96 versus 0.82), accuracy (0.89 versus 0.72), and the predictive value of a positive test (0.95 versus 0.75). The measurement of serum thyroglobulin had a low sensitivity (0.3) in the study but had a specificity of 1.0. Conclusion. It was concluded that iodine‐131 sodium scintigraphy is superior to thallium‐201 scintigraphy and serum thyroglobulin estimation for the detection of residual or metastatic differentiated thyroid carcinoma. However, the use of combined modalities provides a higher diagnostic yield. Thallium‐201 scintigraphy was especially useful in cases in which iodine‐131 scintigraphy was negative and quantitative thyroglobulin levels were elevated.