18F-fluoromethylcholine (FCho), 18F-fluoroethyltyrosine (FET), and 18F-fluorodeoxyglucose (FDG) for the discrimination between high-grade glioma and radiation necrosis in rats: A PET study

Introduction Discrimination between (high-grade) brain tumor recurrence and radiation necrosis (RN) remains a diagnostic challenge because both entities have similar imaging characteristics on conventional magnetic resonance imaging (MRI). Metabolic imaging, such as positron emission tomography (PET) could overcome this diagnostic dilemma. In this study, we investigated the potential of 2-[ 18 F]-fluoro-2-deoxy-D-glucose ( 18 F-FDG), O-(2-[ 18 F]-fluoroethyl)-L-tyrosine ( 18 F-FET), and [ 18 F]-Fluoromethyl-dimethyl-2-hydroxyethylammonium ( 18 F-fluoromethylcholine, 18 F-FCho) PET in discriminating high-grade tumor from RN. Methods We developed a glioblastoma (GB) rat model by inoculating F98 GB cells into the right frontal region. Induction of RN was achieved by irradiating the right frontal region with 60Gy using three arcs with a beam aperture of 3×3mm (n=3). Dynamic PET imaging with 18 F-FDG, 18 F-FET, and 18 F-FCho, as well as 18 F-FDG PET at a delayed time interval (240min postinjection), was acquired. Results MRI revealed contrast-enhancing tumors at 15days after inoculation (n=4) and contrast-enhancing RN lesions 5–6months postirradiation (n=3). On 18 F-FDG PET, the mean lesion-to-normal ratio (LNR mean ) was significantly higher in GB than in RN (p=0.034). The difference in the LNR mean between tumors and RN was higher on the late 18 F-FDG PET images than on the PET images reconstructed from the last time frame of the dynamic acquisition (this is at a conventional time interval). LNRs obtained from 18 F-FCho PET were not significantly different between GB and RN (p=1.000). On 18 F-FET PET, the LNR mean was significantly higher in GB compared to RN (p=0.034). Conclusions Unlike 18 F-FCho, 18 F-FDG and 18 F-FET PET were effective in discriminating GB from RN. Interestingly, in the case of 18 F-FDG, delayed PET seems particularly useful. Advances in knowledge and implications for patient care Our results suggest that (delayed) 18 F-FDG and 18 F-FET PET can be used to discriminate GB (recurrence) from RN. Confirmation of these results in clinical studies is needed.