Prognostic value of dynamic FET-PET in re-irradiation in recurrent malignant glioma

Objectives The aim of the present study was to evaluate factors predicting progression-free survival (PFS) as well as survival in patients with recurrent malignant glioma (MG) before and after re-irradiation including base-line F18-FET-PET imaging.

Methods 56 patients with recurrent MG treated with re-irradiation and a pretherapeutic F18-FET-PET were retrospectively analyzed; post-therapeutic F18-FET-PET imaging was available in 39 cases. For this study, the biological tumor volumes (BTV) were calculated using a volumetric assessment of increased F18-FET-uptake (SUVmax/BG ≥ 1.8) by means of a threshold-based calculation of a volume of interest (VOI). According to the extract time-activity-curves (TAC) for each individual slice with suspicious FET-uptake 5 groups were classified: 1-2 (strongly + mainly increasing), 3 (mixed 1:1) and 4-5 (mainly + strongly decreasing). SUVmax/BG, SUVmean/BG as well as F18-FET uptake kinetics were analyzed according to their prognostic value.

Results The SUVmax/BG decreased significantly after re-irradiation (p < 0.001). The change in SUVmean/BG was not significant (p = 0.09). The BTV decreased significantly, too (p = 0.007). Patients within the kinetic groups 4-5 had a significantly worse survival (P = 0.04) than the other two groups. Multivariate analysis showed that histologic grade, KPS and the kinetic group were independent significant predictors for survival after re-irradiation. For PFS, KPS and histologic grade were significant, too, and kinetics marginally significant (p = 0.08).

Conclusions The uptake kinetics of F18-FET-PET seems to be an independent determinant of both overall and progression-free survival; it may provide valuable additional prognostic information to the WHO histological grading