[¹⁸F]Fluoroethyltyrosine–Positron Emission Tomography-Based Therapy Monitoring after Stereotactic Iodine-125 Brachytherapy in Patients with Recurrent High-Grade Glioma

Abstract

Therapy monitoring of glioma after stereotactic iodine-125 brachytherapy (SBT) remains challenging because posttherapeutic changes in magnetic resonance imaging can mimic tumor progression. We evaluated the prognostic value of serial [18F]fluoroethyltyrosine (FET)-positron emission tomographic (PET) scans for therapy monitoring of high-grade glioma (HGG) after SBT. Thirty-three patients with recurrent HGG were included. Serial FET-PET scans were performed prior to therapeutic intervention and at 3-month intervals during the first year after SBT. FET-PET evaluation was performed by both conventional data analysis and kinetic analysis. Prognostic factors were obtained from proportional hazard models. Median local progression-free survival (LPFS) was 11.1 months. Maximal standardized background uptake value (SUVmax/BG) and biologic tumor volume (BTV) differentiated accurately between therapeutic effects and local tumor progression at the 6-month and subsequent examinations. Increasing uptake kinetics at baseline (p < .05) and during follow-up (p < .01) were stringently associated with a longer LPFS. Early increase in FET uptake after SBT is not unequivocally associated with tumor progression; it might be induced by reactive changes and could easily lead to a misclassification of the tumor status (pseudoprogression). Six months after SBT (or later), however, increased SUVmax/BG and BTV values are associated with a worse prognosis. Multivariate analysis stresses the prognostic importance of dynamic studies.

Dynamic 18F-FET PET in Newly Diagnosed Astrocytic Low-Grade Glioma Identifies High-Risk Patients

“…The study was approved by the ethical review board of the University of Munich. All patients gave written informed consent before each 18 F-FET PET investigation as part of the clinical routine.…”

“…In a first visual analysis, tumors were evaluated qualitatively and categorized in 18 F-FET-negative lesions (with reduced or equal uptake when compared with healthy brain tissue) and 18 F-FET-positive lesions (with uptake greater than the cortical background activity [BG]). …”

“…Forty-minute dynamic 18 F-FET PET scans were acquired with an ECAT Exact HR1 scanner (Siemens) according to standard protocols (12,14).…”

“…In recent years, dynamic PET using the amino acid analog 18 F-fluorethyltyrosine ( 18 F-FET) has gained increasing interest, as it was shown to reliably depict glioma tissue. Furthermore, additional information for differentiation between low-and high-grade gliomas by kinetic analysis has been proposed by various groups (9)(10)(11)(12) but is still a matter of controversy.…”

“…In the current study, we systematically investigated the prognostic value of dynamic 18 F-FET PET analysis, including both static and kinetic parameters, for a large cohort of patients with newly diagnosed astrocytic low-grade glioma.…”