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

Abstract PET using O-(2-[ 18 F]fluoroethyl)- L -tyrosine ( 18 F-FET) allows improved imaging of tumor extent of cerebral gliomas in comparison to MRI. In experimental brain infarction and hematoma, an unspecific accumulation of 18 F-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 18 F-FET uptake in the area of reactive gliosis in the vicinity of untreated and irradiated rat gliomas. Methods F98-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 18 F-FET. Brains were removed, cut in coronal sections and autoradiograms of 18 F-FET distribution were produced and compared with histology (toluidine blue) and reactive astrogliosis (GFAP staining). 18 F-FET uptake in the tumors and in areas of reactive astrocytosis was evaluated by lesion to brain ratios (L/B). Results Large F98-gliomas were present in all animals showing increased 18 F-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 18 F-FET-uptake than the tumors (L/B: 1.5 ± 0.4 vs. 3.9 ± 1.1). The area of 18 F-FET-uptake in the tumor was congruent with histological tumor extent in 31/33 animals. In 2 rats irradiated with 150 Gy, however, high 18 F-FET uptake was noted in the area of astrogliosis which led to an overestimation of the tumor size. Conclusions Reactive astrogliosis in the vicinity of gliomas generally leads to only a slight 18 F-FET-enrichment that appears not to affect the correct definition of tumor extent for treatment planning.