P05.02.A 18F-FACBC PET/MRI in diagnostic assessment of gliomas

Abstract

Abstract Background and Theory MRI and histopathological tissue sampling are routinely done as part of the diagnostic work-up of patients with glioma. MRI provides anatomical images with high resolution and excellent soft-tissue contrast. But this modality has limitations in identifying tumor grade, true tumor extension and differentiate viable tumor tissue from treatment induced changes. PET can provide quantitative information of cellular activity and metabolism, and may therefore have additional value compared to MRI alone. Objective The aim of this study was to find the sensitivity of [18F]FACBC PET in gliomas, and evaluate if PET imaging with this tracer can improve differentiation between low-and high-grade gliomas. Methods Patients with suspicion of primary (n=19) or recurrent gliomas (n=8) were recruited to this study from St. Olavs hospital, Trondheim University Hospital, Trondheim, and from the University Hospital of North Norway, Tromsø. PET acquisitions (30-45 min post injection) using the amino acid radiotracer [18F]FACBC (3 MBq/kg) were performed simultaneously to MRI acquisitions (T1 with and without contrast, FLAIR, and UTE for attenuation correction. The sensitivity of [18F]FACBC PET in glioma detection was assessed using histopathology as reference. Tumor-to-background ratios (TBRs) were compared to tumor subtype and grade to assess the diagnostic value of this tracer for glioma diagnostics. Results Histopathology revealed 2 WHO grade 1 gliomas (pilocytic astrocytoma n=1, pilocytic astrocytoma/ganglioglioma n=1), 7 WHO grade 2 gliomas(astrocytoma n=4, oligodendroglioma n=3), 7 WHO grade 3 gliomas(astrocytoma n=5, oligodendroglioma n=2) and 12 WHO grade 4 tumors(astrocytoma n=1, glioblastoma n=11). [18F]FACBC PET provided a sensitivity of 74.1% in the detection of gliomas. PET uptake was observed in all grade 4 tumors, 5/7 grade 3 tumors, 2/7 grade 2 tumors, and all grade 1 tumors. TBRpeak was high with a median value of 9.4 (range: 2.1-34.9) in PET positive tumors. Only tumors with a TBRpeak > 2.0 were detected with [18F]FACBC PET. TBRpeak was highest for grade 1 gliomas with a median value of 20.6, and increased significantly from grade 2 to grade 4 tumors with median values of 1.7 (grade 2), 6.2 (grade 3) and 12.4 (grade 4) (Kruskal-Wallis, p=0.001). Conclusion [18F]FACBC PET demonstrated high uptake in the majority of gliomas, and there was a clear tendency to higher uptake in the higher grade tumors. [18F]FACBC PET may be useful in the differentiation between glioms grades and subtypes. A future study using the same patient data will be performed to evaluate the assessment of [18F]FACBC PET in neurosurgical treatment planning. Image-localized biopsies from different regions of each tumor will be correlated to fused PET/MRI images to evaluate if [18F]FACBC PET can be used to guide surgical resection and to improve accuracy in histopathological tissue sampling.