EANM insights on PET-based response assessment in neuro-oncology: things are moving forward!

Positron emission tomography (PET) imaging is increasingly recognized as a valuable adjunct to magnetic resonance imaging (MRI) in neuro-oncology, particularly for differentiating tumor progression from treatment-related changes in gliomas and brain metastases. While PET-based response assessment is well established in extracranial malignancies, its implementation in brain tumors is still evolving. The recent development of the PET Response Assessment in Neuro-Oncology (PET RANO) criteria, PET RANO 1.0 for gliomas and PET RANO BM 1.0 for brain metastases, marks a significant advance toward standardizing PET-based monitoring using amino acid tracers such as [ 11 C]MET, [ 18 F]FET, and [ 18 F]F-DOPA. These criteria define thresholds for measurable lesion and categorize response based on metabolic tumor volume and tumor-to-background ratios, independent of clinical or MRI-based measures. Further prospective validation is needed to confirm their reproducibility, robustness, and added value in various therapeutic contexts. While no PET RANO criteria currently exist for meningiomas or central nervous system (CNS) lymphomas, advances in somatostatin receptor (SSTR) PET for meningiomas and [ 18 F]FDG PET for CNS lymphomas underscore the necessity for developing standardized frameworks in these entities. The integration of PET into response monitoring offers a promising avenue to complement MRI, improve therapeutic evaluation, and inform clinical decision-making. Future efforts must focus on multicenter validation, harmonization of acquisition protocols, and incorporation into prospective trials. The adoption of PET RANO criteria in neuro-oncology stands to enhance precision medicine, particularly in the context of novel therapies, and may ultimately support their translation into routine clinical practice.