Distinguishing recurrent tumor and radiation necrosis with positron emission tomography versus stereotactic biopsy

With the recent approval of reimbursement for positron emission tomography (PET), it has become important to clarify the utility of this diagnostic study. We evaluated the utility of PET to distinguish radiation necrosis from recurrent tumor in a retrospective review of patients with primary glial neoplasms. Fifteen patients had preoperative contrast-enhanced MRI and PET images followed by stereotactic biopsy or craniotomy and histological confirmation. The sensitivity of PET was 43% (6/14) and the specificity was 100% (1/1). We examined the sensitivity of PET as a function of volumetric contrast enhancement on MRI. Eighty percent of true-positive PET studies occurred with volume enhancement greater than 10 cm(3). Seventy-five percent of false negatives occurred with volume enhancement less than 6 cm(3). Given the clinical significance of distinguishing tumor progression from radiation necrosis, we believe that PET is insufficient to resolve radiation necrosis versus tumor progression.