Delayed [18F]-FDG PET Imaging Increases Diagnostic Performance and Reproducibility to Differentiate Recurrence of Brain Metastases From Radionecrosis

Abstract

Purpose Differentiating brain metastasis recurrence from radiation necrosis can be challenging during MRI follow-up after stereotactic radiotherapy. [18F]-FDG is the most available PET tracer, but standard images performed 30 to 60 minutes postinjection provide insufficient accuracy. We compared the diagnostic performance and interobserver agreement of [18F]-FDG PET with delayed images (4-5 hours postinjection) with the ones provided by standard and dual-time-point imaging. Methods Consecutive patients referred for brain [18F]-FDG PET after inconclusive MRI were retrospectively included between 2015 and 2020 in 3 centers. Two independent nuclear medicine physicians interpreted standard (visually), delayed (visually), and dual-time-point (semiquantitatively) images, respectively. Adjudication was applied in case of discrepancy. The final diagnosis was confirmed histologically or after 6 months of MRI follow-up. Areas under the receiver operating characteristic curves were pairwise compared. Results Forty-eight lesions from 46 patients were analyzed. Primary tumors were mostly located in the lungs (57%) and breast (23%). The median delay between radiotherapy and PET was 15.7 months. The final diagnosis was tumor recurrence in 24 of 48 lesions (50%), with histological confirmation in 19 of 48 lesions (40%). Delayed images provided a larger area under the receiver operating characteristic curve (0.88; 95% confidence interval [CI], 0.75-0.95) than both standard (0.69; 95% CI, 0.54-0.81; P = 0.0014) and dual-time-point imaging (0.77; 95% CI, 0.63-0.88; P = 0.045), respectively. Interobserver agreement was almost perfect with delayed images (κ = 0.83), whereas it was moderate with both standard (κ = 0.48) and dual-time-point images (κ = 0.61). Conclusions [18F]-FDG PET with delayed images is an accurate and reliable alternative to differentiate metastasis recurrence from radiation necrosis in case of inconclusive MRI after brain stereotactic radiotherapy.