Are Dual-Phase 18F-FDG PET-mpMRI Diagnostic Performances to Distinguish Brain Tumour Radionecrosis/Recurrence after Cranial Radiotherapy usable in routine?

Abstract Purpose: Radionecrosis is a complex challenge in the post-radiotherapy management of these patients due to the difficulty to distinguish this complication from local tumour recurrence. MRI alone have a variable specificity and sensibility as well as PET-CT imaging. We aimed to investigate the diagnostic performance of dual-phase [18F]-FDG PET-MRI to distinguish cerebral radionecrosis from local tumor recurrence after cranial radiotherapy. Materials and Methods: A retrospective analysis was conducted on patients who underwent dual-phase [18F]-FDG PET-MRI between May 2021 and September 2022. Inclusion criteria encompassed patients with inconclusive MRI findings post-radiotherapy and history of cerebral radiotherapy for primary or metastatic brain lesions. Lesions are assessed qualitatively and semi-quantitatively, with sensitivity and specificity calculations. The gold standard to assess radionecrosis was histopathology or a composite criteria at three months. The ethics committee approved the study (N° 2023-034 9th march 2023). Results: The study evaluated 24 lesions in 23 patients. Qualitative analysis yielded 85.7% sensitivity and 75% specificity. Semi-quantitative analysis, based on contralateral background noise, achieved 100% sensitivity and 50% specificity. Moreover, using contralateral frontal lobe background noise resulted higher performances with 92% sensitivity and 63% specificity. Stratification by lesion type demonstrated a 100% sensitivity and specificity rates for metastatic lesions. Conclusions: This study demonstrated the potential of dual-phase [18F]-FDG PET-MRI to distinguish cerebral radionecrosis from local recurrence. The method showed promising diagnostic performance, particularly in semi-quantitative data for metastatic lesions. This study sheded light on the importance of combined PET and MRI data and presented perspectives for a better post-therapeutic differential diagnosis.