COMPARISON OF SERUM THYROGLOBULIN, I-131 AND TL-201 SCINTIGRAPHY IN THE POSTOPERATIVE FOLLOW-UP OF DIFFERENTIATED THYROID-CANCER

To evaluate the significance of Tl-201 scintigraphy, I-131 scintigraphy and serum thyroglobulin (Tg) levels in the postoperative follow-up of differentiated thyroid carcinoma, 86 patients were examined. Serum Tg was found to have the highest sensitivity (97%) as well as specificity (100%) for the detection of local tumour or metastases. Sensitivity and specificity of I-131 scintigraphy after a therapeutic dose of 6100 MBq were 77 and 98%, respectively. For a diagnostic dose of 185 MBq I-131, sensitivity and specificity were 57 and 98%; for 74 MBq Tl-201 these figures were 55 and 91%, respectively. The combination of serum Tg and I-131 had a sensitivity of 100% and a specificity of 98% to detect the presence, although not always the localization, of persistent or recurrent tumour. Tl-201 scintigraphy can provide useful additional information about the localization of local recurrences and metastases, especially in cases where serum Tg becomes positive and I-131 uptake is absent. One has to bear in mind the possibility of discrepant results of I-131 and Tl-201 scintigraphy, in different tumour sites in one patient. There appeared to be no specific tendency for differential uptake of I-131 versus Tl-201 in relation to tumour type (papillary versus follicular) or localization with the possible exception of a higher preference for I-131 uptake in cases of micrometastases of papillary cancer in the lungs.