Intraindividual comparison of F-18-FLT PET and F-18 FET PET in brain tumor patients

To compare findings on FLT PET with FET PET, we prospectively undertaken FLT, FET and FDG PET in same patient with suspected primary/metastatic and recurrent brain tumors. Seventeen studies in 16 patients (47 8.3 years, M: F 10: 6) with brain tumor (3 for initial diagnosis, 6 for therapeutic response, 6 for detecting recurrence, 1 for diagnosis and recurrence both) were included. Brain tumors were 14 gliomas (6 high- grade 9 low-grade by the WHO classification), 2 metastatic brain tumors and 1 CNS lymphoma. 18F-FDG, FLT and FET PET were performed within two weeks. Attenuation-corrected brain images were acquired 30 minutes after injection of 370-555 MBq FDG, FLT and FET with a dedicated PET scanner (ECAT HR scanner, Siemens-CTI). Maximum SUV (max SUV) and relative uptake defined by FLT and FET accumulation within the tumor in relation to a contralateral control region (max SUV for tumor/ mean SUV for contralateral normal gray matter) were calculated. 26 tumor foci were analyzed. Relative FLT uptake (4.17 2.4, 0.58 to 7.45) was grater than than FET uptake (2.03 1.17, 0.92 to 4.53 (p<0.0006)) and FDG uptake (1.16 0.34, 0.76 to 2.08). Among FLT, FET and FDG uptakes in 20 tumor foci, correlation were poor. the relative FLT uptake of high-grade glioma was higher than low-glioma (6.070.76 vs 3.11 2.15, p=0.002), however, relative FET uptake was not different significantly (2.68 1.51, high-grade vs 1.970.78, low-grade). The correlation between tumor grade (high vs low grade) and relative uptake (FLT and FET) was shown only with relative FLT uptake (r=0.62, p=0.002). The best cut off value of relative FLT uptake between high-grade and low-grade glioma was 4.54 (AUC: 0.89 sensitivity: 100 specificity: 86.7%). Compared with FET uptake, FLT uptake showed much higher contrast and associated with tumor grade. Further study, evaluation of proliferative index of Ki-67 and its relationship with FLT and FET uptake, are ongoing