Germ cell tumor: Differentiation of viable tumor, mature teratoma, and necrotic tissue with FDG PET and kinetic modeling

PURPOSE: To evaluate the feasibility of positron emission tomography (PET) with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) in patients with germ c ell tumor (CCT) to monitor treatment and differentiate residual masses afte r chemotherapy. MATERIALS AND METHODS: Twenty-six FDG PET studies were performed in 21 pati ents with CCT. FDG uptake of tumors was interpreted visually, and the lean standardized uptake value (SUVlean) was determined. Tumor kinetic rate cons tants (K1, k2, k3) and net rate of FDG phosphorylation (K = [K1.k3]/[k2 + k 3]) in tumors were calculated from the dynamic data by means of a three-com partment model, assuming k4 = 0. RESULTS: Viable tumors (n = 10) showed intense FDC uptake and could easily be differentiated visually from mature teratoma (n = 6) and necrosis or sca r (n = 10). The SUVlean of residual viable tumors (4.51 +/- 1.34 [mean +/- SD]) was higher than that of mature teratoma (1.38 +/- 0.71) and necrosis o r scar (1.05 + 0.29) (P < .05). Although neither the visual interpretation nor SUVlean differentiated mature teratoma from necrosis or scar, there wer e statistically significant differences in the kinetic rate constants K1 an d K between mature teratoma and necrosis or scar as follows: K1, 0.113 mL/m in/g +/- 0.026 versus 0.036 mL/min/g +/- 0.005 (P < .05); K, 0.005 mL/min/g +/- 0.003 versus 0.0008 mL/min/g +/- 0.0001 (P < .05). CONCLUSION: FDC PET with kinetic analysis appears to be a promising method for management of disease in patients with CCT after treatment.