NIMG-29. ADVANCED MRI BIOMARKERS PREDICT EARLY RESPONSE TO TUMOR TREATING FIELDS IN GLIOBLASTOMA

Abstract

Abstract BACKGROUND Tumor-treating fields (TTFields) is a novel US FDA-approved antimitotic treatment modality for patients with newly diagnosed and recurrent glioblastoma, shown to improve both OS and PFS (Stupp et al 2015). Yet, how to best monitor response to TTfields remains unclear. Conventional (anatomic) MRI is unreliable, often showing initial early radiographic progression followed by tumor regression and clinical benefit, thereby delaying confirmation of response. To address this limitation, we evaluate the utility of quantitative (physiologic) MRI biomarkers. METHODS Patients with newly diagnosed or recurrent IDH wildtype glioblastoma who underwent MRI with DSC-MRI perfusion imaging at 1-2, 3-4 and 5-6 months after TTField treatment were retrospectively identified for this study. Delta T1 (dT1) images were created from standardized (calibrated) pre- and post-contrast T1-weighted images, from which an enhancing lesion volume was objectively determined. Standardized and leakage-corrected relative cerebral blood volume (sRCBV) images were created from the DSC-MRI data. Together, dT1 and sRCBV were used to generate class maps of fractional tumor burden (FTB), which identify highly-vascular and avascular (treatment effect) regions within contrast-enhancement. Kaplan-Meier survival analysis was performed to determine if positive versus negative changes in these metrics, at each time-point relative to pre-treatment values, are predictive of survival. RESULTS 20 patients with newly diagnosed (n=17) or recurrent (n=4) IDH wildtype glioblastoma with a mean TTField compliance of 74.9% were identified. At 1-2 months no metric predicted a survival difference, consistent with the known 4-week delay in tumor stabilization following TTField therapy. At months 3-4 and 5-6 decreasing dT1-determined enhancing volumes showed a survival benefit (p=0.0081, p=0.03). Likewise, a decreasing percentage of highly-vascular tissue, determined from FTB class maps, demonstrated a survival benefit (p=0.0013). CONCLUSIONS Quantitative MRI metrics, including dT1-derived enhancing volumes and FTB/sRCBV-defined regions of high vascularity, demonstrate an ability to provide early indicators of response to TTField treatment.