172 Chapter 7 ABSTRACT Background Brain metastases occur in ten to thirty percent of the adult cancer population. Treatment consists of different (palliative) options, including stereotactic radiosurgery (SRS). Sensitive MRI biomarkers are needed to better understand radiotherapy-related effects on cerebral physiology and the subsequent effect on neurocognitive functioning. Methods In the current study, we used physiological imaging techniques to assess cerebral blood flow (CBF), oxygen extraction fraction (OEF), cerebral metabolic rate of oxygen (CMRO2) and cerebrovascular reactivity (CVR) before and three months after SRS in nine patients with brain metastases. Results Results showed improvement in OEF, CBF and CMRO2 within brain tissue that recovered from edema (all p ≤ .04), while CVR remained impacted. We observed a global post-radiotherapy increase in CBF in healthy-appearing brain tissue (p = .02). Repeated-measures correlation analysis showed larger reductions within regions exposed to higher radiotherapy doses in CBF (rrm = -.286, p < .001), CMRO2 (rrm = -.254, p < .001), and CVR (rrm = -.346, p < .001), but not OEF (rrm = -.004, p = .954). Case analyses illustrated the impact of brain metastases progression on the post-radiotherapy changes in both physiological MRI measures and cognitive performance. Conclusion Our preliminary findings suggest no radiotherapy effects on physiological parameters occurred in healthy-appearing brain tissue within 3-months postradiotherapy. Nevertheless, as radiotherapy can have late side effects, larger patient samples allowing meaningful grouping of patients and longer follow-up are needed.
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