P03.25.b Clinical Utility of [18f]fet Pet in Patients With Circumscribed Astrocytic Glioma

BACKGROUND O-(2-[18F]fluoroethyl)-L-tyrosine ([¹⁸F]FET) PET is predominantly applied for molecular imaging of diffuse gliomas. In contrast, data on the clinical utility of [¹⁸F]FET PET in circumscribed astrocytic gliomas (CAG) remain scarce. MATERIAL AND METHODS We retrospectively identified adult CAG patients who underwent [¹⁸F]FET PET imaging (i) before diagnosis, (ii) at suspected relapse, or (iii) for response assessment at three institutions. Maximum and mean tumor-to-brain ratios (TBRmax, TBRmean) and metabolic tumor volumes were assessed according to the PET RANO 1.0 criteria. Diagnostic performance in differentiating treatment-related changes from tumor relapse was evaluated using ROC analysis and Fisher’s exact test. RESULTS We evaluated 79 [¹⁸F]FET PET scans of 42 patients, including nine (21%) with actionable molecular targets. 65% of CAG WHO grade 1 and 100% of CAG WHO grades 2 or 3 had measurable [¹⁸F]FET uptake according to the PET RANO 1.0 criteria. In these patients, TBR values of CAG WHO grades 2 or 3 were significantly higher than in pilocytic astrocytomas (P<0.01). There was no significant difference in TBR between CAG with or without actionable targets (P>0.05). Following various treatments, response assessment according to the PET RANO 1.0 criteria differed from changes in MRI in 5 of 11 patients (45%). Treatment-related changes were confirmed neuropathologically or clinicoradiologically in 12 patients (43%). In CAG WHO grades 2 or 3, the accuracy of [¹⁸F]FET PET to identify treatment-related changes was 82% using single PET scans and 100% using serial PET imaging (P<0.05). CONCLUSION [¹⁸F]FET PET can add valuable information for the clinical management of patients with CAG.