Methionine positron emission tomography of recurrent metastatic brain tumor and radiation necrosis after stereotactic radiosurgery: is a differential diagnosis possible?

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Abstract
Object. In this study the authors examined how to differentiate radiation necrosis from recurrent metastatic brain tumor following stereotactic radiosurgery by using positron emission tomography (PET) with l-[methyl-11C]methionine (MET). Methods. In 21 adult patients with suspected recurrent metastatic brain tumor or radiation injury, MET-PET scans were obtained. These patients had previously undergone stereotactic radiosurgery and subsequent contrast-enhanced magnetic resonance (MR) examinations before nuclear medicine imaging. Positron emission tomography images were obtained as a static scan of 10 minutes performed 20 minutes after injection of 370 MBq of MET. On MET-PET scans, the portion of the tumor with the highest accumulation of MET was selected as the region of interest (ROI), and the ratio of tumor tissue to normal tissue (T/N) was defined as the mean counts of radioisotope per pixel in the tumor divided by the mean counts per pixel in normal gray matter. The standardized uptake value (SUV) was...