Specific radiosensitivity of brain structures (areas or regions) and cognitive impairment after focal or whole brain radiotherapy: A review

Delayed neurocognitive impairment is observed following encephalic radiotherapy, including brain parts (areas), leading to a substantial deterioration of the quality of life. These delayed radiotherapy side effects are variable in terms of intensity of symptoms and time of occurrence, characterized by minor-to-severe cognitive deficits, such as attention or memory disorders and/or dysexecutive syndrome. However, the precise mechanisms leading to these cognitive disorders remain mostly unknown. Various tissue alterations have been reported after brain radiotherapy, in specific brain structures as the hippocampus, the cerebral white matter or the cerebral cortex. Sparing these structures during brain radiotherapy may be a potential approach to limit the development of late cognitive impairment; however, few dose constraints have been published regarding brain areas (regions) involved in cognitive functions. The main purposes of this literature review are to report the pathophysiological process leading to the radiation-induced cognitive impairment, to describe the tolerance and radiological modifications induced by radiation of specific healthy cerebral tissues, to better understand their radiosensitivity and to describe potential improvements.