18F-FACBC and 18F-FDG PET/MRI in the evaluation of 3 patients with primary central nervous system lymphoma: a pilot study

Abstract

Background: This PET/MRI study compared contrast-enhanced MRI, ¹⁸F-FACBC-, and ¹⁸F-FDG-PET in the detection of primary central nervous system lymphomas (PCNSL) in patients before and after high-dose methotrexate chemotherapy. Three immunocompetent PCNSL patients with diffuse large B-cell lymphoma received dynamic ¹⁸F-FACBC- and ¹⁸F-FDG-PET/MRI at baseline and response assessment. Lesion detection was defined by clinical evaluation of contrast enhanced T1 MRI (ce-MRI) and visual PET tracer uptake. SUVs and tumor-to-background ratios (TBRs) (for ¹⁸F-FACBC and ¹⁸F-FDG) and time-activity curves (for ¹⁸F-FACBC) were assessed.

Results: At baseline, seven ce-MRI detected lesions were also detected with ¹⁸F-FACBC with high SUVs and TBRs (SUV_max:mean, 4.73, TBR_max: mean, 9.32, SUV_peak: mean, 3.21, TBR_peak:mean: 6.30). High TBR values of ¹⁸F-FACBC detected lesions were attributed to low SUV_background. Baseline ¹⁸F-FDG detected six lesions with high SUVs (SUV_max: mean, 13.88). In response scans, two lesions were detected with ce-MRI, while only one was detected with ¹⁸F-FACBC. The lesion not detected with ¹⁸F-FACBC was a small atypical MRI detected lesion, which may indicate no residual disease, as this patient was still in complete remission 12 months after initial diagnosis. No lesions were detected with ¹⁸F-FDG in the response scans.

Conclusions: ¹⁸F-FACBC provided high tumor contrast, outperforming ¹⁸F-FDG in lesion detection at both baseline and in response assessment. ¹⁸F-FACBC may be a useful supplement to ce-MRI in PCNSL detection and response assessment, but further studies are required to validate these findings. Trial registration ClinicalTrials.gov. Registered 15th of June 2017 (Identifier: NCT03188354, https://clinicaltrials.gov/study/NCT03188354 ).

Keywords: 18F-FDG; MRI 18F-FACBC; PCNSL; PET.