Narrow interval dual time point 18F-FDG PET/CT: A practical approach for distinguishing radiation necrosis from tumor recurrence in brain metastasis
Abstract
Introduction: Brain metastases are routinely treated by radiation therapy, surgery, or a combination of both. Patients with tumor recurrence (TR) or radiation necrosis (RN) can present similarly both clinically and on brain magnetic resonance imaging (MRI). In such patients, [18F]-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) scans are often used to aid in the differentiation between these 2 diagnoses. Prior studies have demonstrated higher sensitivity and specificity of FDG-PET for tumor evaluation by using dual time point imaging, also known as dual phase imaging, in various organs. Our study demonstrates the efficacy of a narrow interval dual phase imaging with FDG-PET in distinguishing TR from RN by using the interval of 30 minutes for first scan and 90 minutes for second scan after tracer injection.
Methods: 35 consecutive patients (22 female, 13 male) with various cancer subtypes, lesion size > 1.0 cm3, and suspected recurrence on brain magnetic resonance imaging (MRI) underwent narrow interval dual phase FDG-PET/CT (30 and 90 min after tracer injection). Clinical outcome was determined via sequential MRIs or pathology reports. Maximum standard uptake value (SUVmax) of lesion (L), gray matter (GM), and white matter (WM) was measured on early (1) and delayed (2) imaging. Analyzed variables include % change, late phase, and early phase for L uptake, L/GM uptake, and L/WM uptake. Statistical analysis (P < .01), receiver operator characteristic (ROC) curve and area under curve (AUC) cutoff values were obtained.
Results: Change in L/GM ratio of > −2% was 95% sensitive, 91% specific, and 93% accurate (P < .001, AUC = 0.99) in distinguishing TR from RN. Change in SUVmax of lesion alone was the second-best indicator (P < .001, AUC = 0.94) with an ROC cutoff > 30.5% yielding 86% sensitivity, 83% specificity, and 84% accuracy. Other variables (L alone or L/GM ratios in early or late phase, all L/WM ratios) were significantly less accurate.
Conclusion: Utilizing narrow interval dual phase FDG-PET/CT in patients with brain metastasis treated with radiation therapy provides a practical approach to distinguish TR from RN. Narrow time interval allows for better patient comfort, greater efficiency of PET/CT scanner, and lower disruption of workflow.