MRI based physiological parameters are biomarkers of tumor and non tumor tissue response following radiation to brain metastases

We sought to determine the utility of early relative blood volume (rCBV), relative blood flow (rCBF) and permeability (K2 trans) measurements as biomarkers of radiation response or progression for brain metastases and to characterize early normal tissue changes following stereotactic radiosurgery. Patients were imaged with dynamic susceptibility and dynamic contrast enhanced magnetic resonance imaging at baseline, 1 week and 1 month post-treatment. Tumors outcomes were stratified using volumetric data obtained from structural images. K2trans at 1 week and rCBV at 1 month were identified as predictors of tumor response and progressive disease respectively. Pre-treatment localized dose planning CT images with overlaid isodose distributions outside the tumor were evaluated within all tissue, and segmented gray and white matter. rCBV and rCBF ratio differences between baseline, 1 week and 1 month were compared. Subsequent analysis identified increases in rCBF and rCBV ratios occurring in a dose, tissue, and time specific manner.