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

Background This PET/MRI study compared contrast-enhanced MRI, 18 F-FACBC-, and 18 F-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 18 F-FACBC- and 18 F-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 18 F-FACBC and 18 F-FDG) and time-activity curves (for 18 F-FACBC) were assessed. Results At baseline, seven ce-MRI detected lesions were also detected with 18 F-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 18 F-FACBC detected lesions were attributed to low SUV background . Baseline 18 F-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 18 F-FACBC. The lesion not detected with 18 F-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 18 F-FDG in the response scans. Conclusions 18 F-FACBC provided high tumor contrast, outperforming 18 F-FDG in lesion detection at both baseline and in response assessment. 18 F-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 ).