Quantitative PET studies in pretreated melanoma patients: A comparison of 6-[F-18] fluoro-L-dopa with F-18-FDG and O-15-water using compartment and noncompartment analysis

The purpose of the study was to evaluate the 6-[F-18]fluoro-L-dopa (FDOPA) kinetics with PET in patients with treated melanoma metastases and to compa re it with the standard tracer F-18-FDG as well as with the perfusion trace r O-15-water in selected cases. Methods: The study included 11 patients (22 lesions) with pretreated metastatic melanomas. Dynamic studies with FDG an d in selected cases with O-15-water (eight patients) preceded the FDOPA stu dy. A one-tissue-compartment model was used for the evaluation of the FDOPA and O-15-water studies, and a two-tissue-compartment model and Patlak anal ysis were used for the FDG data. A noncompartment model based on chaos theo ry was used for calculating fractal dimension, which is a parameter for het erogeneity. Results: The FDG studies showed a 1.5-fold increased uptake in comparison with surrounding tissue in 19 of 22 metastatic lesions (sensitiv ity of 86.4%). False-negative FDG results were obtained in 2 patients (thre e lesions). FDOPA uptake was enhanced in 14 of 22 metastatic lesions (sensi tivity of 64%). FDG uptake was 1.5-fold higher than FDOPA uptake in 18 of 2 2 metastases from melanoma, whereas FDOPA uptake was 1.5-fold higher than F DG uptake in 2 patients with liver metastases. The data did not show a stat istically significant correlation between the transport constant (K1) for F DOPA and that for FDG or between the standardized uptake value for FDOPA an d FDG in metastases. No statistically significant correlation was found bet ween K1 for FDOPA and that for O-15-water. The data show that FDOPA uptake is not perfusion dependent and provides different information from FDG. The fractal dimension was similar for all tracers within the tumor region. Det ectability of metastases was enhanced when both tracers were used (sensitiv ity of 95%). Conclusion: In patients with negative FDG findings, FDOPA can help to identify viable melanoma metastases and thus may help to select pat ients who would benefit from further treatment.