F18 FET PET/CT in Brain Tumors Abdelwahab, M.A and Omar, W. NCI, Cairo University. Egypt.

18F-fluoro-ethyl-tyrosine (18F-FET) was developed in the late 1990s first synthesized by Wester and colleagues (1). Providing an 18F-labeled amino acid PET tracer based on f18- fluro-alkylation of disodium salt of L-Tyrosine, with a (110 minutes) half-life, which is more suitable for routine clinical applications than other C11 labeled PET tracers (eg. C11 methionine) (2). FET is an artificial amino acid taken up into up regulated tumoral cells but not incorporated into proteins (contrary to natural amino acids such as 11C methionine) .18F-FET allows good-contrast images to be obtained in both high- and low-grade tumors (3). After a surge of published clinical studies in the last decade, applications of FET PET in brain tumor imaging have been comprehensively reviewed in many studies (4, 5 and 6).
Mechanisms of Tumoral Uptake of Amino Acid PET Radiotracers: System L amino acid transporters (e.g.: LAT1, LAT2, LAT3, and LAT4) transport a variety of neutral amino acids. LAT1 is widely expressed in cancers and plays an essential role in the survival and growth of tumors (3) LAT2 is predominantly expressed in other cell types and carries small neutral amino acids (7) whereas LAT3 and LAT4 have a narrower substrate selectivity (preferring phenylalanine). Other transport systems, including system A, xCT, glutamine, and cationic amino acid transporters, have been explored for tumor imaging with radiolabeled amino acids (8,9) Still, system L currently appears to be the most suitable for brain tumor imaging due to its activity at the blood-brain barrier (8).