Abstract
PURPOSE: Amino acid positron emission tomography (PET) is increasingly utilized in the clinical workup of patients with glioma. To better understand the PET characteristics of IDH-mutant glioma according to the 2021 WHO classification of CNS tumours, this retrospective study explored the association between amino acid PET and magnetic resonance imaging (MRI) characteristics in patients with newly diagnosed IDH-mutant glioma. METHODS: Patients with histologically verified IDH-mutant glioma who underwent [(18)F]FET PET/CT scans without prior treatment were included. PET parameters (PET-positivity according to PET RANO 1.0 criteria, maximal and mean tumour-to-background ratio (TBR(max), TBR(mean)), PET volume and uptake kinetics including minimal time-to-peak (TTP(min))) were assessed and compared with neuropathological findings and contrast-enhanced MRI including Dice similarity coefficients for spatial overlap between PET and MR signals. RESULTS: A total of 147 patients were included (79 astrocytomas, 68 oligodendrogliomas). Contrast enhancement was present in 44/147 tumours (29.9%), most frequently in astrocytoma WHO grade 4 (8/9, 88.9%). [¹⁸F]FET PET was positive in 62/68 oligodendrogliomas (91.2%) and 35/79 astrocytomas (44.3%), with significantly higher uptake intensities in oligodendrogliomas (median TBR(max) 2.43 vs. 1.55; p < 0.001) and increasing values with WHO grade. PET–CE spatial overlap was generally low (median Dice 0.26 (range: 0.01–0.90)), whereas PET–FLAIR overlap was higher (median Dice 0.55 (range: 0.05–0.99)) and showed significant differences between histologies and grades. Dynamic [¹⁸F]FET PET data were available in 91/147 tumours (61.9%) and demonstrated predominantly increasing kinetics (61.5%). In the TTP(min) analysis, WHO grade 4 astrocytomas clustered in the early 12.5-min group, whereas WHO grade 2–3 gliomas showed later peaks (17.5–35 min). CONCLUSION: [(18)F]FET PET uptake intensity correlates positively with the CNS WHO grade in IDH-mutant gliomas, but with marked overlap between tumour grades, and provides complementary information to contrast-enhanced MRI. [(18)F]FET PET may therefore add another layer of information on tumour characteristics and should be further investigated as a complementary biomarker.