IDH1 and astrocytoma (excluding glioblastoma): For astrocytomas, which typically exhibit faster growth (annual diameter increase of 8–10 mm) compared to oligodendrogliomas (4–6 mm/year), volumetric analysis (see General Management Principles) is particularly valuable for capturing their aggressive behavior and identifying patients who may require immediate RT and chemotherapy versus those suitable for watchful waiting or IDH-targeted therapies like vorasidenib (17).