P15.15.B DIFFUSE ADULT-TYPE GLIOMA INFILTRATION DEFINED ON FET-PET

Abstract

Abstract BACKGROUND O-(2-[18F]fluoroethyl)-L-tyrosine (FET)-PET is a valuable tool in glioma imaging used to the definition of biopsy site, monitoring of treatment response and differentiation of treatment-related changes from glioma progression The physiological uptake within reactive astrogliosis may limits FET-PET ability to precisely define glioma extent. For the implementation of FET-PET into clinical trials, a methodological PET standardization is urgently needed to enable more precise and reproducible FET PET quantification. The primary aim of our study was to define a glioma infiltration using threshold based method between astrogliosis and tumoral tissue in FET-PET. RESULTS Astrogliosis presented similar uptake to grade 2 glioma samples. Standard threshold method (1,6x uptake in contralateral brain) in PET aquisiton 40-60 minutes post injection is effective but the accuracy decrease outside contrast enhancement within FLAIR to 56% sensitivity and 41% specificity. Adding second aquisition increased sensitivity within FLAIR to 71%. Finally, using tumor-to-plexus ratio, it is possible to differentiate astrogliosis and grade 2, and achieve sensitivity of 73% and specificty of 84% within FLAIR or 90% sensitivity with 61% specificity. ROC curves are significantly different related to method used with best results specific to new strategy. CONCLUSION Determining glioma extent using standard threshold method in PET or FLAIR is limited. Improving is possible with dual aquisition and/or different tumor to background ratio. This may largely improve delineation of glioma for surgery or radiotherapy.