# Clinical potential of [18F]FET PET in patients with circumscribed astrocytic glioma

## TL;DR

[18F]FET PET imaging helps in managing circumscribed astrocytic gliomas by detecting disease and distinguishing treatment effects from tumor relapse.

## Contribution

Demonstrates the clinical utility of [18F]FET PET in CAG management, particularly for treatment response assessment.

## Key findings

- Measurable [18F]FET uptake was observed in 65% of WHO grade 1 and 100% of WHO grade 2 and 3 CAG.
- TBR values were significantly higher in WHO grade 2 and 3 CAG compared to pilocytic astrocytomas.
- Serial [18F]FET PET imaging achieved 100% accuracy in identifying treatment-related changes in CAG WHO grades 2 or 3.

## Abstract

To investigate the clinical potential of O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) PET imaging in the management of circumscribed astrocytic gliomas (CAG), a rare glioma subtype with limited imaging data.

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.

We evaluated 79 [18F]FET PET scans of 42 patients, including nine (21%) with actionable molecular targets. Measurable [18F]FET uptake was observed in 65% of WHO grade 1 and 100% of WHO grade 2 and 3 CAG. TBR values were significantly higher in WHO grade 2 and 3 CAG than in pilocytic astrocytomas (P < 0.01), but showed no difference based on molecular target status (P > 0.05). In 5 of 11 patients (45%), treatment response assessment by PET RANO 1.0 differed from MRI. Treatment-related changes were confirmed 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).

[18F]FET PET can contribute to clinical management of patients with CAG by detecting measurable disease, differentiating treatment-related changes from tumor progression, and showing potential in treatment response assessment through longitudinal imaging.

The online version contains supplementary material available at 10.1007/s00259-025-07654-9.