Radiation necrosis of central nervous system studied by PET

The hypothesis being tested is that radiation necrosis can be separated from regrowth of tumor by comparative studies using tracers which reflect different physiological functions. Nine patients treated for CNS tumors were referred because fo onset of neurologic deterioration and were studied by Rb-82 and 18-FDG using the Donner 280-crystal PET. Ten to 15 mCi of Rb-82 was injected i.v. and three PET sections 1 cm thick collected. Next, 8 to 12 mCi of FDG was injected and dynamic PET was performed at a level of high suspicion. Usually five transverse sections spanning the region of suspected pathology are acquired. Patients with active FDG and Rb accumulation in suspicious anatomical areas were diagnosed as tumor recurrence. Regions of Rb accumulation but no FDG accumulation received a tentative diagnosis of early radiation necrosis. Regions with no tracer accumulation represent either effective treatment or radiation necrosis. Three patients with diagnosis of radiation necrosis without regrowth of tumor have been confirmed by biopsy; four patients with recurrent tumor were correctly diagnosed and the remaining patients are being followed serially and have not yet had a confirmation procedure performed. The criteria for regrowth of tumor appears to be sound, however, lack of tracer uptake cannot be specific for radiation necrosis unless there is a progression in sequential studies. These PET studies have been of substantial aid to the neurosurgeons in planning treatment of brain tumor patients