Evaluating Physiological MRI Parameters in Patients with Brain Metastases Undergoing Stereotactic Radiosurgery—A Preliminary Analysis and Case Report

Abstract

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 effects on neurocognitive functioning. 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. The results showed improvement in OEF, CBF and CMRO2 within brain tissue that recovered from edema (all p ≤ 0.04), while CVR remained impacted. We observed a global post-radiotherapy increase in CBF in healthy-appearing brain tissue (p = 0.02). A repeated measures correlation analysis showed larger reductions within regions exposed to higher radiotherapy doses in CBF (rrm = −0.286, p < 0.001), CMRO2 (rrm = −0.254, p < 0.001), and CVR (rrm = −0.346, p < 0.001), but not in OEF (rrm = −0.004, p = 0.954). Case analyses illustrated the impact of brain metastases progression on the post-radiotherapy changes in both physiological MRI measures and cognitive performance. Our preliminary findings suggest no radiotherapy effects on physiological parameters occurred in healthy-appearing brain tissue within 3-months post-radiotherapy. Nevertheless, as radiotherapy can have late side effects, larger patient samples allowing meaningful grouping of patients and longer follow-ups are needed.

CO2 as an engine for neurofluid flow: Exploring the coupling between vascular reactivity, brain clearance, and changes in tissue properties

“…24 Although in this case the intracranial volume will be the same, the brain compliance will decrease, making it more difficult to quickly accommodate transient volume changes from CBV dynamics. It is also important to note that patients with a higher tumor and edema load demonstrated reduced baseline perfusion (see previous research focusing on a subset of the same patient cohort 16 , 25 ) and negative BOLD responses in associated regions ( Figure 4 ). This effect can arise because of flow redistribution, also known as “vascular steal”, which occurs in regions where the CVR response is impaired.…”

“…In a previous study focusing on a subset of the same patient cohort, no significant change in CVR was found between preradiotherapy and postradiotherapy. 16 Consequently, the focus of the study was primarily on changes related to edema. However, changes in total tumor mass will also influence mechanical properties and could have implications for CVR and CSF flow.…”

“…Data were retrospectively selected from the ongoing Assessing and Predicting Radiation Influence on Cognitive Outcome using the cerebrovascular stress Test (APRICOT) study. 16 The cohort consists of adult patients (age ≥ 18 years) with either radiographic and/or histologic proof of brain metastases that were referred to the radiotherapy department of the UMC Utrecht (UMCU) for radiotherapy treatment. Patients were scanned prior to and approximately 3 months after radiotherapy.…”