COMPARISON OF (18)FDG-PET WITH (131)IODINE AND TC-99M-SESTAMIBI SCINTIGRAPHY IN DIFFERENTIATED THYROID-CANCER

(18)Fluorine-fluorodeoxyglucose (FDG) positron-emission tomography (PE T) has emerged as a useful method in various fields of oncology. The a im of the present study was to evaluate the clinical significance of t his technique in differentiated thyroid carcinoma and to compare the r esults with other imaging modalities, particularly with whole-body (13 1)iodine scintigraphy (WBS) and hexakis (2-methoxyisobutylisonitrile) (99m)technetium (I) scintigraphy (MIBI). Whole-body PET imaging using I;DG was performed in 54 patients. There were 39 patients with papilla ry tumors and 15 patients with follicular tumors (including 3 Hurthle- cell carcinomas). Primary tumor stage (pT) was pT1 in 5 cases, pT2 in 19 cases, pT3 in 2 cases, pT4 in 24 cases, and unknown in 4 cases, res pectively. Finally, for each case an overall clinical evaluation was d one including histology, cytology, thyroglobulin level, sonography, co mputed tomography, magnetic resonance imaging, and subsequent clinical course, to allow a comparison with functional imaging results. Compar ed with WBS, FDG-PET gave different results in the majority of cases w ith recurrence/metastases (11 FDG-true-positive/WBS-negative tumor sit es and 8 WBS-true-positive/FDG-negative tumor sites). In 7 patients wi th recurrence/metastases, FDG-PET and WBS gave corresponding results ( 10 sites). In 28 patients, FDG-PET and WBS were normal (including 2 fa lse-negative cases). MIBI was performed in 44 cases. FDG-PET was bette r correlated to MIBI (congruent positive results in 13 tumor sites) th an to WBS. Compared with MIBI, FDG-PET was superior in 5 cases (includ ing 3 patients with distant metastases). Two FDG-negative/MIBI-positiv e tumors were. observed. Different tracer uptake mechanisms have to be considered regarding ''nonspecific'' tumor imaging with FDG-PET or MI BI. Nevertheless, since spatial resolution with respect to tomographic imaging is inferior with single photon emission computer tomography ( SPECT) using MTBI, the observed higher sensitivity of PET might be due to the higher spatial resolution of this method. As far as grading co uld be obtained, FDG-PET seemed to be more sensitive than WBS in high- grade tumors, whereas WBS was positive predominantly in low-grade carc inomas, although statistical significance could not be reached. The re sults prove the clinical usefulness of FDG-PET and MIBI for detection of (131)iodine-negative tumor tissue in differentiated thyroid cancer.