(18)F-FACBC PET/MRI in the evaluation of human brain metastases: a case report

BACKGROUND: Patients with metastatic cancer to the brain have a poor prognosis. In clinical practice, MRI is used to delineate, diagnose and plan treatment of brain metastases. However, MRI alone is limited in detecting micro-metastases, delineating lesions and discriminating progression from pseudo-progression. Combined PET/MRI utilises superior soft tissue images from MRI and metabolic data from PET to evaluate tumour structure and function. The amino acid PET tracer (18)F-FACBC has shown promising results in discriminating high- and low-grade gliomas, but there are currently no reports on its use on brain metastases. This is the first study to evaluate the use of (18)F-FACBC on brain metastases. CASE PRESENTATION: A middle-aged female patient with brain metastases was evaluated using hybrid PET/MRI with (18)F-FACBC before and after stereotactic radiotherapy, and at suspicion of recurrence. Static/dynamic PET and contrast-enhanced T1 MRI data were acquired and analysed. This case report includes the analysis of four (18)F-FACBC PET/MRI examinations, investigating their utility in evaluating functional and structural metastasis properties. CONCLUSION: Analysis showed high tumour-to-background ratios in brain metastases compared to other amino acid PET tracers, including high uptake in a very small cerebellar metastasis, suggesting that (18)F-FACBC PET can provide early detection of otherwise overlooked metastases. Further studies to determine a threshold for (18)F-FACBC brain tumour boundaries and explore its utility in clinical practice should be performed.