Dynamic 18F-FET PET is a powerful imaging biomarker in gadolinium-negative gliomas.

Background: We aimed to elucidate the place of dynamic 18F-FET-PET in prognostic models of gadolinium (Gd)-negative gliomas.

Methods: In 98 patients with Gd-negative gliomas undergoing 18F-FET-PET guided biopsy, time activity curves (TAC) of each tumor were qualitatively categorized as either increasing or decreasing. Additionally, post-hoc quantitative analyses were done using minimal time-to-peak (TTPmin) measurements. Prognostic factors were obtained from multivariate hazards models. The fit of the biospecimen- and imaging-derived models was compared.

Results: A homogeneous increasing, mixed, and homogeneous decreasing TAC pattern was seen in 51, 19, and 28 tumors, respectively. Mixed TAC tumors exhibited both increasing and decreasing TACs. Corresponding adjusted 5-years survival was 85%, 47%, and 19%, respectively (p<0.001). Qualitative and quantitative TAC measurements were highly inter-correlated (p<0.0001): TTPmin was longest (shortest) in the homogeneous increasing (decreasing) TAC group and in between in the mixed TAC group. TTPmin was longer in IDH-mutant tumors (p<0.001). Outcome was similarly precisely predicted by biospecimen- and imaging-derived models. In the biospecimen model, WHO grade (p<0.0001) and IDH status (p<0.001) were predictors for survival. Outcome of homogeneous increasing (homogeneous decreasing) TAC tumors was nearly identical with both TTPmin >25 min (TTPmin ≤12.5 min) tumors and IDH-mutant grade II (IDH-wildtype) gliomas. Outcome of mixed TAC tumors matched that of both intermediate TTPmin (>12.5 min and ≤25 min) and IDH-mutant, grade III gliomas. Each of the three prognostic clusters differed significantly from the other ones of the respective models (p<0.001).

Conclusion: TAC measurements constitute a powerful biomarker independent from tumor grade and IDH status.