PET/SPECT, Menzel, C

Abstracts XIX Brazilian Congress of Nuclear Medicine

9. PET/SPECT

9.5 - FDG-PET DURING THERAPY AND FOLLOW-UP OF DIFFERENTIATED THYROID CARCINOMA

Menzel, C; Grünwald, F; Biersack, H - University of Bonn Department of Nuclear Medicine & Bonn- Germany

menzel@mailer.meb.uni-bonn.de

The scintigraphy with radioiodine (RI) has the main impact on the treatment of differentiated thyroid carcinomas (DTC) as it generates diagnostic and prognostic information. The detection of RI-negative tumor-tissue, however, canges the strategy of therapy. The value of FDG-PET to detect RI-negative tumor-tissue was prospectively evaluated in 54 patients (39 papillar, 15 follicular DTC). Most cases showed a flip-flop phenomenon of either RI or FDG uptake within the tumor, namely 11 true positive FDG/RJ negative- and 8 true positive RI / FDG-negative cases. In 7 cases there were true positive results being obtained with both methods (FDG / RI), although in part being located differently. In 28 cases true negative results were found with the RI- and the FDG-scan. The histological tumor type showed no significant influence on the result, while the sensitivity of FDG increased during TSH-suppression. The sensitivity of the FDG-PET (FDG) was 69%, the specificity was 100 %, and the accuracy was 85 %. In comparison, the radioiodine-scan (RI) showed a sensitivity of 58 %, a specificity of 100 %, and an accuracy of 80 %. In conclusion, FDG-PET is an important and accurate tool for in-vivo grading of tumor or metastases of DTC and for the exclusion of RI-negative tumor tissue especially in low differentiated DTC as this changes the therapy regimen from radioiodine therapy to other, still potentially curative therapy modalities (surgery, ext. radiation, redifferentiation).