207 Summary parameters is dependent on the vascular status of the underlying tissue. Metrics related to CVR exhibited potential to identify vascular risk in tissue prior to visible perfusion deficits on ASL MRI. Chapter 7 evaluated the impact of radiotherapy on both metabolic and vascular reserve in patients with BMs by assessing CBF, oxygen extraction fraction (OEF), cerebral metabolic rate of oxygen (CMRO2), and CVR before and three months after radiotherapy in nine APRICOT-patients. Whole-brain CBF increased after radiotherapy, potentially reflecting restorative mechanisms against radiationinduced brain inflammation. Ongoing vascular damage was observed alongside metabolic recuperation in regions with resolved edema. Regional analysis revealed that CBF, CMRO2, and CVR deteriorated in a dose-dependent manner, with larger deteriorations in regions exposed to higher doses. However, notable patient and dose region heterogeneity was observed, especially at low doses. Case analysis suggests some of the heterogeneity may be linked to tumor response. Though caution must be taken due to the study’s preliminary nature and case-analysis, results suggest no substantial radiotherapy-induced brain damage within the three months after treatment, but instead highlight the parameters’ possible susceptibility to identify both restoration of or ongoing metabolic or vascular damage following radiotherapy. 8
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