Clinical impact of [18F]FET-PET/CT in differentiating treatment-associated changes and tumor progression in adult-type diffuse gliomas

Abstract Background MRI follow-up of diffuse glioma patients often results in diagnostic uncertainty between treatment-associated changes (TAC) and true progressive disease (PD). While [18F]FET-PET improves diagnostic accuracy, research on clinical impact and optimal clinical timing is scarce. This study evaluates the clinical impact of adding [18F]FET-PET to MRI in cases of uncertainty and effect of timing between immediate [18F] FET-PET use (≤6 weeks after first MRI with new or increasing enhancement) versus delayed use (>6 weeks). Methods This single-center retrospective cohort study included adult glioma patients (grade 2-4) who underwent [18F]FET-PET due to uncertainty regarding PD versus TAC on MRI. Primary outcome was a clinical policy change based on [18F]FET-PET results. Secondary outcomes included policy change validity, unnecessary interventions (ie diagnostic or therapeutic interventions that could have been prevented with early correct diagnosis), and diagnostic accuracy (based on pathology or radiological follow-up). All outcomes, except diagnostic accuracy, were compared between immediate and delayed [18F]FET-PET groups. Results Of 41 included patients, 78% had glioblastoma and 54% received chemoradiation. Policy changes occurred in 22 cases (54%), of which 18 (82%) were supported by clinicoradiological follow-up or pathology. No significant difference in policy changes was found between immediate and delayed [18F]FET-PET groups. Unnecessary interventions, including chemotherapy and MRI scans, occurred only in the delayed group. Conclusion In this retrospective analysis, [18F]FET-PET influences clinical decision-making in over half of cases, and performing [18F]FET-PET at the earliest possible time likely prevents unnecessary interventions. Larger prospective studies are needed to confirm its clinical value and optimal timing.