Comparison of 18F-GE-180 and dynamic 18F-FET PET in high grade glioma: a double-tracer pilot study

Background PET represents a valuable tool for glioma imaging. In addition to amino acid tracers such as 18 F-FET, PET targeting the 18-kDa mitochondrial translocator-protein (TSPO) is of high interest for high-grade glioma (HGG) imaging due to its upregulation in HGG cells. 18 F-GE-180, a novel TSPO ligand, has shown a high target-to-background contrast in HGG. Therefore, we intra-individually compared its uptake characteristics to dynamic 18 F-FET PET and contrast-enhanced MRI in patients with HGG. Methods Twenty HGG patients (nine IDH -wildtype, 11 IDH -mutant) at initial diagnosis ( n = 8) or recurrence ( n = 12) were consecutively included and underwent 18 F-GE-180 PET, dynamic 18 F-FET PET, and MRI. The maximal tumour-to-background ratios (TBR max ) and biological tumour volumes (BTV) were evaluated in 18 F-GE-180 and 18 F-FET PET. Dynamic 18 F-FET PET analysis included the evaluation of minimal time-to-peak (TTP min ). In MRI, the volume of contrast-enhancement was delineated (VOL CE ). Volumes were spatially correlated using the Sørensen–Dice coefficient. Results The median TBR max tended to be higher in 18 F-GE-180 PET compared to 18 F-FET PET [4.58 (2.33–8.95) vs 3.89 (1.56–7.15); p = 0.062] in the overall group. In subgroup analyses, IDH -wildtype gliomas showed a significantly higher median TBR max in 18 F-GE-180 PET compared to 18 F-FET PET [5.45 (2.56–8.95) vs 4.06 (1.56–4.48); p = 0.008]; by contrast, no significant difference was observed in IDH -mutant gliomas [3.97 (2.33–6.81) vs 3.79 (2.01–7.15) p = 1.000]. Only 5/20 cases showed higher TBR max in 18 F-FET PET compared to 18 F-GE-180 PET, all of them being IDH -mutant gliomas. No parameter in 18 F-GE-180 PET correlated with TTP min ( p > 0.05 each). There was a tendency towards higher median BTV GE-180 [32.1 (0.4–236.0) ml] compared to BTV FET [19.3 (0.7–150.2) ml; p = 0.062] with a moderate spatial overlap [median Sørensen–Dice coefficient 0.55 (0.07–0.85)]. In MRI, median VOL CE [9.7 (0.1–72.5) ml] was significantly smaller than both BTV FET and BTV GE180 ( p