Biopsy validation of 18F-DOPA PET and biodistribution in gliomas for neurosurgical planning and radiotherapy target delineation: results of a prospective pilot study

Background. Delineation of glioma extent for surgical or radiotherapy planning is routinely based on MRI. There is increasing awareness that contrast enhancement on T1-weighted images (Ti-CE) may not reflect the entire extent of disease. The amino acid tracer F-18-DOPA (3,4-dihydroxy-6-[18F] fluoro-L-phenylalanine) has a high tumor-to-background signal and high sensitivity for glioma imaging. This study compares F-18-DOPA PET against conventional MRI for neurosurgical biopsy targeting, resection planning, and radiotherapy target volume delineation. Methods. Conventional MR and F-18-DOPA PET/CT images were acquired in 10 patients with suspected malignant brain tumors. One to 3 biopsy locations per patient were chosen in regions of concordant and discordant F-18-DOPA uptake and MR contrast enhancement. Histopathology was reviewed on 23 biopsies. F-18-DOPA PET was quantified using standardized uptake values (SUV) and tumor-to-normal hemispheric tissue (T/N) ratios. Results. Pathologic review confirmed glioma in 22 of 23 biopsy specimens. Thirteen of 16 high-grade biopsy specimens were obtained from regions of elevated F-18-DOPA uptake, while T1-CE was present in only 6 of those 16 samples. Optimal F-18-DOPA PET thresholds corresponding to high-grade disease based on histopathology were calculated as T/N > 2.0. In every patient, F-18-DOPA uptake regions with T/N > 2.0 extended beyond Ti-CE up to a maximum of 3.5 cm. SUV was found to correlate with grade and cellularity. Conclusions. F-18-DOPA PET SUVmax more accurately identify regions of higher-grade/higher-density disease in patients with astrocytomas and will have utility in guiding stereotactic biopsy selection. Using SUV-based thresholds to define high-grade portions of disease may be valuable in delineating radiotherapy boost volumes.