RESUMO
PURPOSE: To assess the utility of 18F-fluoroethyl-L-tyrosine (FET) positron emission tomography/magnetic resonance imaging (PET/MRI) in distinguishing recurrence from radionecrosis. MATERIALS AND METHODS: Thirty-two patients (25 males, 7 females) of glioma who had already undergone surgery/chemoradiotherapy and had enhancing brain lesions suspicious of recurrence were evaluated using integrated 18F-FET PET/MRI, and followed up with histopathology or clinical follow-up and/or MRI/PET/MRI imaging. Manually drawn regions of interest over areas of maximal enhancement or FET uptake were used to calculate tumor to background ratios [TBRmax, TBRmean], choline: creatine ratio [Cho: Cr ratio], normalized relative cerebral blood volume [N rCBVmean] and apparent diffusion coefficient [ADCmean]. Correlations were evaluated using Pearson's coefficient. Accuracy of each parameter was calculated using independent t-test and receiver operator curve (ROC) analysis while utility of all four parameters together using multivariate analysis of variance (MANOVA) for differentiating recurrence vs. radionecrosis was evaluated. Positive histopathology and imaging/clinical follow up served as the gold standard. RESULTS: Twenty-four of the 32 patients were diagnosed with recurrent disease and 8 with radiation necrosis. Significant correlations were observed between TBRmaxand N rCBVmean (ρ =0.503; P = 0.003), TBRmean, and N rCBVmean (ρ =0.414; P = 0.018), TBRmaxand ADCmean (ρ = -0.52; P = 0.002), and TBRmeanand ADCmean(ρ = -0.518; P = 0.002). TBRmax, TBRmean, ADCmean, Cho: Cr ratios, and N rCBVmeanwere significant in differentiating recurrence from radiation necrosis with an accuracy of 94.1%, 88.2%, 80.4%, 96.4%, and 89.9%, respectively. MANOVA indicated that combination of all parameters demonstrated better evaluation of recurrence vs. necrosis than any single parameter. The diagnostic accuracy, sensitivity, and specificity using all MRI parameters were 93.75%, 96%, and 85.7%, and using all FET PET/MRI parameters was 96.87%, 100%, and 85.7%, respectively. CONCLUSIONS: Synergetic effect of multiple MR parameters evaluated together in addition to FET PET uptake highlights the fact that integrated 18F-FET PET/MRI might have the potential to impact management of patients with glioma by timely and conclusive recognition of true recurrence from radiation necrosis.
