Values of 99mTc-methoxyisobutylisonitrile imaging after first-time large-dose 131I therapy in treating differentiated thyroid cancer

Objective: The aim of this study is to investigate the use of Tc-99m-methoxyisobutylisonitrile (MIBI) imaging for evaluating the treatment response of differentiated thyroid cancer (DTC) after the first administration of a high dose of I-131. Methods: Patients with DTC who received I-131 therapy underwent Tc-99m-MIBI imaging after successive increases in the therapeutic dose of I-131, and the serum levels of thyroglobulin (Tg) were measured. Results: A total of 191 patients were enrolled in the final analysis, including 65 metastases and/or thyroid remnant-positive patients (22 patients with metastases and 43 patients with thyroid remnants). The sensitivity of Tc-99m-MIBI imaging for detecting positive cases and thyroid remnants was 56.9% and 39.5%, respectively, which was significantly lower than that of I-131 imaging (92.3% and 100%, respectively, P<0.01 for both). The sensitivity of Tc-99m-MIBI imaging for detecting metastases was 90.9%, which was slightly higher than that of I-131 imaging (77.3%, P>0.05). The Tg levels in the positive group were significantly higher than that in the negative group (P<0.01). In addition, the Tg levels in the Tc-99m-MIBI+/I-131(-) group were significantly higher than that in the I-131(+)/Tc-99m-MIBI group (P<0.05). Conclusion: After the first I-131 therapy, although Tc-99m-MIBI imaging was able to detect the existence of metastatic lesions in patients with DTC better, its assessment for the removal efficiency of thyroid remnants was unsatisfactory. The results of Tc-99m-MIBI imaging showed good correlations with the Tg level.