Preliminary investigation of 18F-FDG PET in radioactive encephalopathy

Objective: To investigate the diagnostic value of 18F-FDG PET (fluorine-18 2-fluoro-2-deoxy-D-glucose-positron emission tomography) in early stage of radioactive encephalopathy. Methods: Total 45 cases were assigned into two groups, 25 patients underwent head-neck radiotherapy, within those patients, 17 had nasopharyngeal neoplasms, 15 had neurologic manifestations and were diagnosed encephalopathy; 20 volunteers served as normal control. All cases were injected 18F-FDG intravenously and PET scan were performed 40 minutes later. Imaging were gathered and reconstructed into transaxial, coronal and sagittal sections. The radioactive uptake ratios of cerebrum to cerebellum were also quantified by semiquantification methods. Results: clear and symmetric brain structures were seen in all sections in healthy volunteers. In radiotherapy group, 14 out of 15 who diagnosed encephalopathy had significant nonsymmetric 18F-FDG distributions. 6 cases had hypometabolic area in temporal lobes, 3 cases in thalamus, 2 cases in cerebellum, 2 cases in parietal lobe, and 1 case in occipital lobe respectively. Conclusion: Radioactive encephalopathy is a common and serious complication of radiotherapy. It could be reversed completely with early diagnosis and treatment. PET, as a kind of functional and metabolic imaging method, could be used as an early and important monitoring aid in the radiotherapy of head and neck neoplasms