Dynamic PET F-18-FDG studies in patients with primary and recurrent soft-tissue sarcomas: Impact on diagnosis and correlation with grading

The purpose of this study was to evaluate F-18-FDG PET studies of primary a nd recurrent sarcomas for diagnosis and correlation with grading. Methods: The evaluation included 56 patients, 43 with histologically proven malignan cies and 13 with benign lesions. Seventeen patients were referred with susp icion on a primary tumor, and the remaining 39 were referred with suspicion on a recurrent tumor. The FDG studies were accomplished as a dynamic serie s for 60 min. The evaluation of the FDG kinetics was performed using the fo llowing parameters: standardized uptake value (SUV), global influx, computa tion of the transport constants K1-k4 with consideration of the distributio n volume (VB) according to a two-tissue-compartment model, and fractal dime nsion based on the box-counting procedure (parameter for the inhomogeneity of the tumors). Results: Visual evaluation revealed a sensitivity of 76.2%, a specificity of 42.9%, and an accuracy of 67.9%. The vascular fraction VB and the SUV were higher in malignant tumors compared with benign lesions ( t test, P < 0.05). Although the FDG SUV helped to distinguish benign and ma lignant tumors, there was some overlap, which limited the diagnostic accura cy. The SUV and fractal dimension accounted for significant differences in six of the nine diagnostic pairs. Whereas grade (G) II and G III tumors wer e differentiated from lipomas on the basis of the fractal dimension and som e other kinetic parameters, no differences were found between G I tumors an d lipomas. On the basis of the discriminant analysis, the differentiation o f soft-tissue tumors was best for the use of six parameters of the FDG kine tics (SUV. VB, K1, k3, influx, and fractal dimension). Eighty-four percent of G III tumors, 37.5% of G II tumors, 80% of G I tumors, 50% of lipomas, a nd 14.3% of scars could be classified correctly, whereas inflammatory lesio ns were misclassified. Conclusion: FDG PET should be used preferentially fo r monitoring patients with G III sarcomas, Visual analysis provides a low s pecificity. In contrast, the evaluation of the full FDG kinetics provides s uperior information, particularly for the discrimination of G I and G III t umors (positive predictive value, >80%).