Influence of Dexamethasone on O-(2-[18F]-Fluoroethyl)-L-Tyrosine Uptake in the Human Brain and Quantification of Tumor Uptake.

Abstract

O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) is an established positron emission tomography (PET) tracer for brain tumor imaging. This study explores the influence of dexamethasone therapy on [18F]FET uptake in the normal brain and its influence on the maximum and mean tumor-to-brain ratio (TBR). [18F]FET PET scans of 160 brain tumor patients were evaluated (80 dexamethasone treated, 80 untreated; each group with 40 men/40 women). The standardized uptake value of [18F]FET uptake in the normal brain (SUVbrain) in the different groups was compared. Nine patients were examined repeatedly with and without dexamethasone therapy. SUVbrain of [18F]FET uptake was significantly higher in dexamethasone-treated patients than in untreated patients (SUVbrain 1.33 ± 0.1 versus 1.06 ± 0.16 in male and 1.45 ± 0.25 versus 1.31 ± 0.28 in female patients). Similar results were observed in patients with serial PET scans. Furthermore, compared to men, a significantly higher SUVbrain was found in women, both with and without dexamethasone treatment. There were no significant differences between the different groups for TBRmax and TBRmean, which could have been masked by the high standard deviation. In a patient with a stable brain metastasis investigated twice with and without dexamethasone, the TBRmax and the biological tumor volume (BTV) decreased considerably after dexamethasone due to an increased SUVbrain. Dexamethasone treatment appears to increase the [18F]FET uptake in the normal brain. An effect on TBRmax, TBRmean, and BTV cannot be excluded which should be considered especially for treatment monitoring and the estimation of BTV using [18F]FET PET.