220 Chapter 9 Heterogeneity of patients with brain metastases Patients with BMs present a heterogeneous group of patients as illustrated by the diverse range of medical histories of patients. This heterogeneity was also reflected in both the cognitive functioning (Chapter 3 and 4) and the physiological MRI parameters (Chapter 6 and 7). For example, cognitive impairments and post-radiotherapy cognitive decline in the BMs population were not confined to one cognitive domain, but rather spanned the whole range of cognitive domains (Chapter 3 and 4). This heterogeneity poses a challenge for research, as we must devise methods to capture and comprehend all the variations. Capturing the cognitive heterogeneity Even though patients with BMs pose a vulnerable population, I have shown that a 90-minute comprehensive NCA is feasible in most patients willing to participate in research (Chapter 3). Besides its feasibility, this test battery was more adept to provide insights into the extent of cognitive impairment in patients with BMs before radiotherapy. As it remains important to accurately identify cognitive changes, an important avenue for future research is to establish a test battery that is sensitive to these changes, elaborate enough to identify changes across the various cognitive domains, yet as short and efficient as possible. Especially in the context of understanding cognitive changes by investigating a multitude of MRI biomarkers, like I did in Chapter 7, utilization of a standardized, yet elaborate cognitive test battery may prove to be the most appropriate approach. One can for example imagine that the Hopkins verbal learning test revised (HVLT-R), which provides measure on immediate recall, learning, delayed recall, recognition as well as response bias, may be a simple yet effective way to capture the multiple aspects of memory functioning with one cognitive test. Another possibility would be to use computerized/online cognitive testing, like the Amsterdam Cognition Scan.49 The Amsterdam Cognition Scan has the ability to capture multiple different variables, like response speed and accuracy, at the same time making it an efficient tool for cognitive testing in a heterogeneous patient population. Consistency in methodologies across studies would be beneficial as it would enable the validation of preliminary findings, like those in Chapter 7, within larger multi-center studies. While the International Cancer and Cognition Task Force ICCTF has made an important step in harmonizing the cognitive tests performed in cancer research and advices against the use of screening tests like the Mini-Mental State Examination (MMSE) or Montreal Cognitive Assessment (MOCA) in cancer research50, continuous evaluation is warranted. Even though not one cognitive test battery can do justice to the complex interplay of cognitive functions, I firmly believe a test battery aimed
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