Malignant gliomas are generally considered to be among the most radioresistant tumors, and are often not accessible to locoregional treatments such as surgery or radiotherapy. With the development of aggressive therapeutic trials, an increasing number of patients are presenting after treatment with symptoms and signs that may be secondary to residual or recurrent tumor, or solely due to radiation-induced changes. However, computed tomography (CT) and magnetic resonance imaging (MRI) offer imperfect discrimination of tumor viability and radionecrosis; indeed, radiation necrosis and treated tumors have similar imaging characteristics. A CT guided biopsy of enhancing areas in the tumor bed may also be unreliable. Functional imaging with SPECT has been used to assess tumor viability and necrosis and has proved to be effective in differentiating recurrent glioma from radiation-induced changes.