18F-DOPA-PET and Advanced MRI Improve Treatment Response Assessment in IDH1/2 -Mutant Gliomas Treated with IDH Inhibitors

PURPOSE: Small-molecule inhibitors targeting isocitrate dehydrogenase (IDH) 1/2-mutant proteins have demonstrated benefit in IDH1/2-mutant gliomas. However, responses assessed by conventional MRI measurements are infrequent, delayed, and difficult to interpret, highlighting the need for early biomarkers of treatment benefit. In this study, we investigated 3,4-dihydroxy-6-[18F]-fluoro-L-phenylalanine positron emission tomography (18F-DOPA-PET) and MRI responses in patients with IDH1/2-mutant glioma receiving IDH inhibitors (IDHi). EXPERIMENTAL DESIGN: Patients with IDH1/2-mutant glioma receiving IDHi as part of trials or expanded access programs with pre- and posttreatment MRI and 18F-DOPA-PET were included. Evaluations included 2D/3D measurements on T2-weighted fluid-attenuated inversion recovery images; T1-post-contrast, perfusion, and diffusion imaging for MRI; and metabolic tumor volume (MTV), total lesion glycolysis, and tumor-to-background ratios (TBR) for 18F-DOPA-PET. Disease response evaluation using volumetric assessments, RANO 2.0, and PET RANO 1.0 criteria were compared and correlated with outcomes. RESULTS: From 2021 to 2025, 20 patients with IDH1/2-mutant glioma (8 with astrocytoma and 12 with oligodendroglioma) receiving IDHi (4 receiving ivosidenib and 16 receiving vorasidenib) were analyzed. Significant reductions in 18F-DOPA-PET parameters including TBRmean, TBRmax, and MTV were observed in 10 of 20 patients, aligning with observed changes in perfusion and diffusion imaging. Nine partial responses and one complete response were identified using 18F-DOPA-PET, whereas both volumetric and standard 2D morphologic MRI assessments indicated stable disease as best response. PET response on MTV was correlated with prolonged tumor control. CONCLUSIONS: These results highlight the potential of 18F-DOPA-PET and advanced MRI sequences as valuable complements to standard RANO 2.0 MRI evaluations for assessing treatment response in patients with glioma undergoing IDHi therapy.