Implementation of 6-[18F]FDOPA PET/CT for management of brain tumors growth and post-irradiation changes: Preliminary results from Azerbaijan

Objectives: The aim of this study is to identify earlier, reliable and effective imaging techniques for detection of recurrences after radiotherapy of patients with brain tumors, thereby enhancing the quality of patients' life. Fortunately, identifying recurrent tumour from abnormal but benign tissue (inflammation/physiological radiotherapy changes) is possible with the use of amino-acid radiopharmaceutical imaging-3,4-dihydroxy-6-18F-fluoro-L-phenylalanine (18F-DOPA) PET-CT which was previously used for the differential diagnosis of movement disorders like Parkinson disease. We have used 18F-DOPA to examine the PET/CT scan for the diagnosis of brain tumors and the selection of treatment methods after radiotherapy. Methods: 24 brain 18F-FDOPA PET/CT with MRI studies were analysed for staging or follow up of brain tumours. Diagnosis of tumour was confirmed histologically by surgical resection/biopsy. Gold standard was considered biopsy when possible or imaging at follow up. Static PET acquisitions were post-reconstructed between the 10th and 20th minute after injection of 18F-FDOPA. Quantitative PET parameters (SUVmax, SUVmean, tumor/striatum ratio (T/S), and tumour/normal brain ratio (T/N) and MRI features (maximal diameters, tumour enhancement, presence of necrosis, cerebral perfusion [CBV, CBF]) were recorded. Volume of tumour was assessed based on areas of maximal visual uptake on PET or enhancement/signal change in the tumour on MRI. Separate ROIs of the specific features (enhancing, non-enhancing and necrotic part) of the tumours and of the normal appearing white matter (NAWM) were drawn on PET. Within these ROIs, SUVmax were recorded. The confidence factor i.e. the presence of viable tumour was assessed by both modalities on a 5 point scale. Results: Tumour lesional size varied between 5 mm and 80 mm. 19 lesions (79%) showed intense tracer uptake and 3 showed necrotic core/component. The mean SUVmax was 3.2 for LGG and 3.9 for HGG. Also mean tumor uptake/normal brain and tumor uptake/striatum were calculated for LGG and HGG (2.6 vs 2.1 and 1.5 vs 1.3). In 18 patients there were concordant on both imaging modalities. Conclusions: This study presents the comparison of a voxel based analysis of 18F-DOPA PET/CT and MRI in glioma patients. The mismatch between 18F-DOPA and MRI parameters indirectly confirms the hypothesis of different biological parameters identified by 18F-DOPA and MRI.