The Role of PET in Differentiation of Recurrent Brain Tumor from Radiation Injury

Objectives: 1) Clarify efficacy and usefulness of FDG-PET for differentiating recurrent tumor from radiation necrosis 2) Compare FDG-PET with alternative modalities and techniques for this purpose3) Discuss the mechanism by which glucose metabolism take place in brain tumor and radiation injuries. Abstract (summary): The incidence of primary intracranial tumors is 7-19 cases per 100,000 people annually. There is an extensive diversity of pathologic subtypes, with gliomas accounting for 45% of all brain tumors. The general strategy for treating brain tumors is surgical resection of solitary lesions in combination with radiation therapy with or without chemotherapy. However, radiation may cause damage to vascular endothelial cells and oligodendrocytes leading to necrosis, axonal swelling, and reactive gliosis. This complication is the major dose-limiting complication of radiotherapy arising months to years after treatment. The consequent clinical manifestations include personality changes, dementia, memory deficits, seizures, and motor impairments. Unfortunately, these symptoms are similar to the recurrence of the brain tumor. Distinguishing between recurrence and radionecrosis is essential in directing therapy. The gold standard method is the biopsy of the lesion which is invasive and can cause severe complications. Other tools like computed tomography (CT) and standard magnetic resonance imaging (MRI) have not been able to reliably distinguish recurrent tumors from radiation-induced changes because both lesions demonstrate increased volume of enhancement, edema, and mass effect. Thus, there is a need for a more reliable clinical tool to overcome this lack of specificity. The use of functional fluorodeoxyglucose-positron emission tomography (FDG-PET) to distinguish recurrent tumor from radionecrosis appeared to be promising. It is known that tumor cells change glucose metabolism due to an increased dependence on anaerobic glycolysis. It was also known that successful radiation treatment resulted in a decreased FDG uptake over time and that tumor necrosis had not FDG uptake. Thus, it was hypothesized that evaluation of glucose consumption can differentiate recurrent tumor from radiation-induced changes. To further clarify this critical function, we aimed to discuss different aspects of PET in differentiation of recurrent brain tumor from radiation injury.