Thallium-avid cerebral radiation necrosis

Thallium imaging has been proposed as a noninvasive method to distinguish recurrent tumor from cerebral radiation necrosis in patients who have undergone radiation therapy. Previous reports have supported the intuitive hypothesis that metabolically active tumor tissue would accumulate Tl-201 to a much higher degree than nonviable necrotic tissue. A case of biopsy-proven cerebral radiation necrosis is presented demonstrating a degree of Tl-201 avidity previously thought to be diagnostic of recurrent tumor. Based on this finding, it is concluded that a high degree of Tl-201 uptake does not exclude the diagnosis of cerebral radiation necrosis.