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

PURPOSE: O-(2-[18 F]fluoroethyl)-L-tyrosine ([18 F]FET) is an established positron emission tomography (PET) tracer for brain tumor imaging. This study explores the influence of dexamethasone therapy on [18 F]FET uptake in the normal brain and its influence on the maximum and mean tumor-to-brain ratio (TBR).

PROCEDURES: [18 F]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 [18 F]FET uptake in the normal brain (SUVbrain ) in the different groups was compared. Nine patients were examined repeatedly with and without dexamethasone therapy.

RESULTS: SUVbrain of [18 F]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 .

CONCLUSION: Dexamethasone treatment appears to increase the [18 F]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 [18 F]FET PET.