Monitoring of Radiochemotherapy in Patients with Glioblastoma Using O -(2-[ 18 F]Fluoroethyl)-L-Tyrosine Positron Emission Tomography: Is Dynamic Imaging Helpful?

Monitoring of radiochemotherapy (RCX) in patients with glioblastoma is difficult because unspecific alterations in magnetic resonance imaging with contrast enhancement can mimic tumor progression. Changes in tumor to brain ratios (TBRs) in positron emission tomography (PET) using O-(2-¹⁸fluoroethyl)-l-tyrosine (¹⁸F-FET) after RCX with temozolomide of patients with glioblastoma have been shown to be valuable parameters to predict survival. The kinetic behavior of ¹⁸F-FET in the tumors is another promising parameter to analyze tumor metabolism. In this study, we investigated the predictive value of dynamic ¹⁸F-FET PET during RCX of glioblastoma. Time-activity curves (TACs) of ¹⁸F-FET uptake of 25 patients with glioblastoma were evaluated after surgery (FET-1), early (7-10 days) after completion of RCX (FET-2), and 6 to 8 weeks later (FET-3). Changes in the time to peak (TTP) and the slope of the TAC (10-50 minutes postinjection) were analyzed and related to survival. Changes in kinetic parameters of ¹⁸F-FET uptake after RCX showed no relationship with survival time. In contrast, the high predictive value of changes of TBR to predict survival was confirmed. We conclude that dynamic ¹⁸F-FET PET does not provide additional prognostic information during RCX. Static ¹⁸F-FET PET imaging (20-40 minutes postinjection) appears to be sufficient for this purpose and reduces costs.