Comparison of 18F-FET and 18F-FDG PET in brain tumors

The purpose of this study was to compare the diagnostic value of positron emission tomography (PET) using [18F]-fluorodeoxyglucose (18F-FDG) and O-(2-[18F]fluoroethyl)-l-tyrosine (18F-FET) in patients with brain lesions suspicious of cerebral gliomas.MethodsFifty-two patients with suspicion of cerebral glioma were included in this study. From 30 to 50 min after injection of 180 MBq 18F-FET, a first PET scan (18F-FET scan) was performed. Thereafter, 240 MBq 18F-FDG was injected and a second PET scan was acquired from 30 to 60 min after the second injection (18F-FET/18F-FDG scan). The cerebral accumulation of 18F-FDG was calculated by decay corrected subtraction of the 18F-FET scan from the 18F-FET/18F-FDG scan. Tracer uptake was evaluated by visual scoring and by lesion-to-background (L/B) ratios. The imaging results were compared with the histological results and prognosis.ResultsHistology revealed 24 low-grade gliomas (LGG) of World Health Organization (WHO) Grade II and 19 high-grade gliomas (HGG) of WHO Grade III or IV, as well as nine others, mainly benign histologies. The gliomas showed increased 18F-FET uptake (>normal brain) in 86% and increased 18F-FDG uptake (>white matter) in 35%. 18F-FET PET provided diagnostically useful delineation of tumor extent while this was impractical with 18F-FDG due to high tracer uptake in the gray matter. A local maximum in the tumor area for biopsy guidance could be identified with 18F-FET in 76% and with 18F-FDG in 28%. The L/B ratios showed significant differences between LGG and HGG for both tracers but considerable overlap so that reliable preoperative grading was not possible. A significant correlation of tracer uptake with overall survival was found with 18F-FDG only. In some benign lesions like abscesses, increased uptake was observed for both tracers indicating a limited specificity of both techniques.Conclusions18F-FET PET is superior to 18F-FDG for biopsy guidance and treatment planning of cerebral gliomas. The uptake of 18F-FDG is associated with prognosis, but the predictive value is limited and a histological evaluation of tumor tissue remains necessary. Therefore, amino acids like 18F-FET are the preferred PET tracers for the clinical management of cerebral gliomas.