Re-irradiation in recurrent malignant glioma: prognostic value of [¹⁸F]FET–PET

The aim of the present study is to determine new positron emission tomography (PET) imaging-related factors predictive of progression-free survival as well as survival in patients with recurrent malignant glioma (MG) prior to and after re-irradiation. Fifty-six patients with recurrent MG who underwent re-irradiation treatment and pretherapeutic dynamic [¹⁸F]-fluoroethyl-l-tyrosine (FET)–PET scan were retrospectively analyzed. The prognostic value of different parameters, such as biological tumor volume, maximal tumor uptake (SUV_max/BG), mean tumor uptake (SUV_mean/BG), as well as uptake kinetics, was evaluated. [¹⁸F]FET uptake kinetics was classified according to a five-point rating as category G_1–2 (strongly/mainly increasing kinetics), G₃ (mixed 1:1), or G_4–5 (mainly/strongly decreasing kinetics). Patients within the pretherapeutic kinetic group G_4–5 had significantly worse survival than the other two groups (p = 0.01). Multivariate analysis revealed that histologic grade, Karnofsky Performance Score (KPS), and kinetic group were independent significant predictors for survival after re-irradiation. The uptake kinetics of [¹⁸F]FET–PET is an independent determinant of overall and to a lesser extent also progression-free survival. Thus, [¹⁸F]FET–PET kinetics may provide valuable additional prognostic information for treatment decisions.