TL-201, TECHNETIUM-99M-TETROFOSMIN AND I-131 IN DETECTING DIFFERENTIATED THYROID-CARCINOMA METASTASES

The purpose of this study was to asses the detectability of differenti ated thyroid carcinoma (DTC) metastases by Tc-99m-tetrofosmin and to c ompare the results of Tc-99m-tetrofosmin with I-131 and Tl-201. The re liability of Tl-201 and Tc-99m-tetrofosmin scanning during supression therapy also has been studied. Methods: A prospective study was perfor med on 41 patients (30 females, 11 males) with DTC (30 papillary, 11 f ollicular) who had undergone total thyroidectomy and received an avera ge dose of 117 mCi (4329 MBq) of radioiodine for ablation of postsurgi cal residual thyroid tissue. All patients (n = 41) had Tl-201, Tc-99m- tetrofosmin or I-131 whole-body imaging after discontinuation of thyro id hormone replacement (thyroxine-off group), Eight of 14 patients wit h distant metastases also were imaged when they were on thyroxine ther apy both with Tl-201 and Tc-99m-tetrofosmin (thyroxine on-and-off grou p). Radiologic studies (chest radiography, CT and MRI), serum thyroglo bulin assays and histopathologic examinations were performed to clarif y the presence of metastases with positive uptake on any of three radi onuclide studies. Results: In 26 of 41 patients all three scans were n egative. These patients also clinically didn't show any evidence of me tastases, Fourteen patients were considered to have distant metastases on the basis of clinical, radiologic and histopathologic findings. Th e sensitivities of Tl-201, Tc-99m-tetrofosmin and I-131 in diagnosing distant metastases were comparable (0.85, 0.85 and 0.78, respectively) . iodine-131 was much more sensitive than Tl-201 and Tc-99m-tetrofosmi n for demonstrating residual thyroid tissue after surgery (1.00, 0.33 and 0.33, respectively). The only false-positive case involved radioio dine uptake in a tuberculoma, Thyroxine-on images of 8 patients with d istant metastases showed no difference from their thyroxine-off images regarding the site, number and uptake of metastases, Conclusion: Tech netium-99m-tetrofosmin and Tl-201 imaging are highly sensitive for det ecting differentiated thyroid carcinoma metastases and do not require prior withdrawal of thyroid hormone suppressive therapy.