189 Physiological MRI Biomarkers & Cognition after SRS for Brain Metastases Figure 8. Visual comparison of MRI-related and cognitive changes in three subjects with different radiotherapy responses. Subject 006 had new brain metastases, subject 007 brain metastases shrinkage and subject 024 had a mixed response whereby some brain metastases grew and some shrunk. Pre- and post-radiotherapy MRI maps are shown separately for pre-radiotherapy (T0) and three months post-radiotherapy (T1). Additionally, the delivered radiotherapy dose and difference scores (T1-T0) for the MRI maps are shown alongside the cognitive changes that were observed across the cognitive domains. Hereby grey indicates stable performance, green improvement, red decline and yellow mixed response. As patient 24 did not perform the CVR assessment post-radiotherapy, no difference maps for CVR are available. DISCUSSION In this study, we employed state-of-the-art physiological imaging techniques to comprehensively evaluate properties linked to both the metabolic and vascular reserve in patients with brain metastases before and three months after SRS. Our findings revealed a significant improvement in metabolic measures (OEF and CMRO2) within brain tissue that recovered from edema three months post-radiotherapy, while the vascular reserve remained impacted. Additionally, we observed a global post-radiotherapy increase in CBF in healthy-appearing brain tissue. No dose-related changes in any of the MRI metrics were detected when regions were categorized into low, medium, and high delivered dose. Correlation analyses highlighted larger reductions in CBF, CMRO2, and CVR within regions exposed to higher radiotherapy doses, but also indicated considerable variability both among patients and across dose regions. Case analyses suggested that part of this heterogeneity may be attributed to brain metastases progression following SRS. Collectively, our findings 7
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