IMG-125. Differentiating tumor progression from pseudoprogression in glioma patients using MR elastography

BACKGROUND Glioma pseudoprogression (psPD) following chemoradiation remains a clinical conundrum as MRI cannot distinguish psPD from true PD. Magnetic resonance elastography (MRE), a noninvasive imaging technique that probes the tumor biomechanical environment, can help characterize elements of tumor heterogeneity and malignant progression. We hypothesize that psPD and true PD will have different biomechanical properties allowing MRE to distinguish between these processes. METHODS Adult patients with high-grade glioma who developed increased contrast uptake on post-contrast T1 within 3 months of completing chemoradiation were recruited from Mass General Brigham and Dana-Farber Cancer Institute. Patients underwent up to 3 longitudinal MRE scans 1-2 months apart. The MRE acquisition used a multi-slice Ristretto sequence synchronized to a vibrational head transducer. The shear modulus was extracted from the MRE data to quantify tissue stiffness. Regions of interest (ROIs) of contrast enhancement (CE) and T2-FLAIR hyperintensity were segmented by a deep-learning tool and verified by a neuro-oncologist. RESULTS Four patients (three with newly diagnosed glioblastoma and one with high-grade glioma not elsewhere classified) completed the longitudinal monitoring study to date. Following chemoradiation, all received adjuvant temozolomide. The median time between completion of chemoradiation and the first MRE was 68 days. In two patients with suspected psPD, stiffness increased in the CE ROI and was stable in the T2-FLAIR ROI. In two patients with PD, stiffness decreased in the CE ROI. CONCLUSIONS Tissue biomechanical properties may help distinguish psPD from true PD as gliosis due to psPD may lead to increased stiffness whereas progressive tumor may lead to decreased stiffness within the CE core because of development of focal micronecrosis. Additional patients are being enrolled to further evaluate the added value of MRE in differentiating psPD from PD.