Health effects of ionizing radiation exposure in the brain: MELODI perspectives on potential implications of emerging evidence for radiation protection.

There is a growing body of epidemiological evidence for elevated risks of a variety of multifactorial diseases such as cancer, neurodegenerative diseases (e.g., Parkinson's disease and dementia) and cerebrovascular diseases (e.g., stroke) following radiation exposure of the brain. Implications of available scientific evidence for radiation protection need to be assessed, e.g., in terms of radiation effect classification (tissue reactions vs stochastic effects), dose and dose-rate effectiveness, target identification (at levels of cells, tissues and organs inside/outside the brain) for dose monitoring and risk management, radiation weighting approach for the mixed radiation field, and individual differences in radiation responses (e.g., with sex, age, populations, genetics, epigenetics, comorbidity, co-exposure). On the other hand, whole brain irradiation has clinically been tested to treat neurodegenerative diseases, particularly Alzheimer's disease. Action of radiation seems to represent a double-edged sword (i.e., detrimental to the healthy brain vs therapeutic to the diseased brain) not only for cancer, but also for non-cancer diseases. Justification of radiation exposure and optimization of radiation protection would therefore be of critical importance. This paper gives a brief overview of emerging evidence for radiation effects in the brain, and considers its potential implications for radiation protection.