Reproducibility of O-(2-¹⁸F-fluoroethyl)-L-tyrosine uptake kinetics in brain tumors and influence of corticoid therapy: An experimental study in rat gliomas

Purpose: Positron emission tomography (PET) using O-(2-¹⁸F-fluoroethyl)-L-tyrosine (¹⁸F-FET) is a well-established method for the diagnostics of brain tumors. This study investigates reproducibility of ¹⁸F-FET uptake kinetics in rat gliomas and the influence of the frequently used dexamethasone (Dex) therapy. Methods: F98 glioma or 9L gliosarcoma cells were implanted into the striatum of 31 Fischer rats. After 10–11 days of tumor growth, the animals underwent dynamic PET after injection of ¹⁸F-FET (baseline). Thereafter, animals were divided into a control group and a group receiving Dex injections, and all animals were reinvestigated 2 days later. Tumor-to-brain ratios (TBR) of ¹⁸F-FET uptake (18–61 min p.i.) and the slope of the time-activity-curves (TAC) (18–61 min p.i.) were evaluated using a Volume-of-Interest (VOI) analysis. Data were analyzed by two-way repeated measures ANOVA and reproducibility by the intraclass correlation coefficient (ICC). Results: The slope of the tumor TACs showed high reproducibility with an ICC of 0.93. A systematic increase of the TBR in the repeated scans was noted (3.7 ± 2.8 %; p < 0.01), and appeared to be related to tumor growth as indicated by a significant correlation of TBR and tumor volume (r = 0.77; p < 0.0001). After correction for tumor growth TBR showed high longitudinal stability with an ICC of 0.84. Dex treatment induced a significant decrease of the TBR (−8.2 ± 6.1 %; p < 0.03), but did not influence the slope of the tumor TAC. Conclusion: TBR of ¹⁸F-FET uptake and tracer kinetics in brain tumors showed high longitudinal stability. Dex therapy may induce a minor decrease of the TBR; this needs further investigation.