Uptake of O-(2-[18F]fluoroethyl)-L-tyrosine in reactive astrocytosis in the vicinity of cerebral gliomas

PET using O-(2-¹⁸F]fluoroethyl)-L-tyrosine (¹⁸F-FET) allows improved imaging of tumor extent of cerebral gliomas in comparison to MRI. In experimental brain infarction and hematoma, an unspecific accumulation of ¹⁸F-FET has been detected in the area of reactive astrogliosis which is a common cellular reaction in the vicinity of cerebral gliomas. The aim of this study was to investigate possible ¹⁸F-FET uptake in the area of reactive gliosis in the vicinity of untreated and irradiated rat gliomas.MethodsF98-glioma cells were implanted into the caudate nucleus of 33 Fisher CDF rats. Sixteen animals remained untreated and in 17 animals the tumor was irradiated by Gamma Knife 5–8 days after implantation (2/50 Gy, 3/75 Gy, 6/100 Gy, 6/150 Gy). After 8–17 days of tumor growth the animals were sacrificed following injection of ¹⁸F-FET. Brains were removed, cut in coronal sections and autoradiograms of ¹⁸F-FET distribution were produced and compared with histology (toluidine blue) and reactive astrogliosis (GFAP staining). ¹⁸F-FET uptake in the tumors and in areas of reactive astrocytosis was evaluated by lesion to brain ratios (L/B).ResultsLarge F98-gliomas were present in all animals showing increased ¹⁸F-FET-uptake which was similar in irradiated and non-irradiated tumors (L/B: 3.9 ± 0.8 vs. 4.0 ± 1.3). A pronounced reactive astrogliosis was noted in the vicinity of all tumors that showed significantly lower ¹⁸F-FET-uptake than the tumors (L/B: 1.5 ± 0.4 vs. 3.9 ± 1.1). The area of ¹⁸F-FET-uptake in the tumor was congruent with histological tumor extent in 31/33 animals. In 2 rats irradiated with 150 Gy, however, high ¹⁸F-FET uptake was noted in the area of astrogliosis which led to an overestimation of the tumor size.ConclusionsReactive astrogliosis in the vicinity of gliomas generally leads to only a slight ¹⁸F-FET-enrichment that appears not to affect the correct definition of tumor extent for treatment planning.