NIMG-36: COMPREHENSIVE EVALUATION OF GLIOMA RECURRENCE WITH SIMULTANEOUS O-(2-18F-FLUOROETHYL)-L-TYROSINE (18F-FET) POSITRON EMISSION TOMOGRAPHY MAGNETIC RESONANCE IMAGING (PET MRI)

BACKGROUND: Simultaneous PET MRI offers opportunity to combine attributes of 18F-FET PET and MRI together during a single examination in the evaluation of post treatment glioma recurrence. The purpose of this study was to examine its potential in distinguishing glioma recurrence vs. radiation necrosis. METHODS: 27 patients with 36 suspicious brain lesions were evaluated with contrast enhanced 18F FET PET MRI using Biograph mMR acquired over 25 min immediately following tracer administration. Dynamic (20/27 patients: 5 data points), and static PET data ( 0 to 25 min) & MR images were analyzed using manually drawn ROI over the area of maximal contrast enhancement and/or FET uptake and migrating the same over corresponding other images to obtain various PET and MR parametric values for analysis. Statistical analysis was done for each parameter individually and in various combinations using Sigma Plot 13.0 and PASW 18. Positive histopathology and long term imaging/clinical follow up served as gold standard. RESULTS: 21 patients were classified as recurrence and 6 patients as radiation necrosis Individually, TBRmax, TBRmean, ADCmean, Cho: Cr ratios and normalized rCBVmean were significant in differentiating recurrence from radiation necrosis with an accuracy of 94.4% for TBRmax, 91% for TBRmean, 83.3% for ADCmean, 94.4% for Cho: Cr ratio and 86.1% for N rCBVmean respectively. TBRmax with Cho: Cr ratio yielded the highest accuracy of 97.2 % (AUC, 0.979± 0.03; sensitivity, 93.1%; specificity, 100%; P< 0.001). TTP & SUVmax of the lesion were found to be most significant parameters in distinguishing between recurrence & radiation necrosis with a p value of <0.05. SUVmax (p < 0.05) & slope to peak (p < 0.05) were most useful in differentiating low grade recurrence from radiation necrosis. CONCLUSION: Simultaneous FET PET MRI offers a quick and comprehensive method in differentiating glioma recurrence and treatment effect with high accuracy.