COMPARISON OF TL-201, TC-99(M)-MIBI AND I-131 IMAGING IN THE FOLLOW-UP OF PATIENTS WITH WELL-DIFFERENTIATED THYROID-CARCINOMA

Problems stemming from the withdrawal of TSH suppressing doses of T4 o r T3 and false-negative studies associated with I-131 scintigraphy hav e justified the search for other radionuclides in the follow-up of pat ients with well-differentiated thyroid carcinoma. Although Tl-201 and Tc-99(m)-MIBI (MIBI) have been suggested as alternatives, their role i n the detection of residual and recurrent disease has yet to be establ ished. We therefore studied 36 patients who had undergone total or nea r total thyroidectomy for well-differentiated thyroid carcinoma to det ermine the imaging potential of Tl-201, MIBI and I-131 in the detectio n of residual or recurrent disease. Eighteen of the 36 patients had un dergone I-131 ablation. Imaging was performed 20 min following the int ravenous injection of 111 MBq Tl-201 or 555 MBq MIBI, or 48 h after th e oral ingestion of 185 MBq I-131. The overall concordance between the (201)T1, MIBI and I-131 scans was 70%. The concordance between thyrog lobulin (TG) levels and the I-131 scans was 78%; that between the Tl-2 01 and MIBI scans and TG levels was 83%. Among the group of pre-ablati ve patients, there were six false-negative results with Tl-201 and thr ee false-negative results with MIBI. Among the post-ablation group, th e Tl-201 and MIBI scans were falsely negative in five patients. The I- 131 scans revealed all known residual or recurrent diseases. In conclu sion, Tl-201, MIBI or TG levels should not be used in the place of I-1 31 for the detection of residual or recurrent thyroid cancer. However, in patients who have not had their TSH suppressing doses of T4 or T3 withdrawn, the role of Tl-201 and MIBI is debatable.