NIMG-39. UTILITY OF PHYSIOLOGIC MR METRICS IN DISTINGUISHING TRUE-PROGRESSION FROM PSEUDOPROGRESSION IN GLIOBLASTOMAS STRATIFIED BY MGMT PROMOTER METHYLATION

Abstract

Abstract BACKGROUND Methylation of O6-methyl-guanine-methyl transferase MGMT gene promoter is associated with favorable prognosis in glioblastoma (GBM) patients treated with surgery and chemoradiation therapy (CRT). OBJECTIVE To investigate potential of diffusion and perfusion MR imaging in distinguishing TP from PsP in GBM patients stratified by MGMT status. METHODS A cohort of 92 patients demonstrating new/increasing enhancing lesions within six months of completion of CRT underwent 3T MR imaging. Median values of mean diffusivity (MD), fractional anisotropy (FA), anisotropy coefficients [linear(CL), planar (CP), and spherical (CS)] and maximum relative cerebral blood volume (rCBVmax) were computed from enhancing lesions. Patients were classified as TP (n=65) and PsP (n=27) based on histopathology or follow-up MRI scans. Mann-Whitney, independent-sample T-tests and receiver operating characteristic (ROC) curve analyses were performed to distinguish TP from PsP. Of 92 patients, MGMT status was available from 60 patients [MGMT-methylated (n=23) and MGMT-unmethylated (n=37)]. Statistical analyses were also performed in distinguishing TP (n=15) and PsP (n=8) from MGMT-methylated and MGMT-unmethylated subgroups (TP=28; PsP=9). A p-value of 0.05 was considered significant. RESULTS Significantly higher rCBVmax and FA and a trend towards higher CP were observed in TP compared to PsP. Among these parameters, rCBVmax had the best sensitivity=62%, specificity=68% and accuracy=67% in distinguishing TP from PsP. ROC analysis revealed sensitivity=54%, specificity=78% and accuracy=68% after combination of these parameters. In MGMT methylated patients, only rCBVmax was significantly higher in TP than in PsP with sensitivity=79%, specificity=67% and accuracy=74% at a threshold rCBVmax value of 2.23. In MGMT unmethylated group, a trend towards higher rCBVmax was observed in TP than in PsP with sensitivity=67%, specificity=77%, accuracy=69%, threshold value=2.89. CONCLUSION Physiologic imaging parameters demonstrate variable diagnostic values for detecting PsP in GBM patients stratified by MGMT status. The best parameter in distinguishing TP from PsP was rCBVmax in patients demonstrating MGMT promoter methylation.