Assessing neurocognitive dysfunction in cranial radiotherapy: Can cognitive event-related potentials help?

Cognitive changes are common sequelae of cancer and cancer treatment, particularly in patients receiving cranial radiotherapy (RT). These effects are typically assessed by subjective clinical examination or using objective neuropsychological tests. Biologically based neurophysiological methods have been increasingly applied to the study of cognitive processing in neuropsychiatric and neurological disorders and as objective measures of cognitive status for patients with dementia. These methods detect the activation of neural circuits that directly mediate cognitive function in the human brain and include metabolic and electrophysiology based techniques. Neuroimaging procedures such as 18FDG PET and more recently fMRI, which detect metabolic activation associated with cognitive processing, provide excellent spatial resolution and can be directly correlated with neuroradiological findings associated with cranial RT neurotoxicity. Clinical electrophysiology procedures such as cognitive event-related potentials (ERP), which detect the neuronal electrical activity associated with cognitive processing, offer excellent temporal resolution at low cost. Cognitive ERP techniques are already being used to assess severity and progression of cognitive dysfunction in patients with vascular and degenerative dementias, but have been largely overlooked in studies of radiation-related cognitive impairments. We review these various electrophysiological methods in the context of their relevance to assessing cranial RT effects on cognitive function, and provide recommendations for a neurophysiological approach to supplement current neuropsychological tests for RT cognitive impairments. This technology is well suited for clinical assessment of neurocognitive sequelae of cancer and should provide new insights into the mechanism of RT-related cognitive dysfunction.