At doses greater than what level does CNS syndrome typically occur leading to elevated fluid content of the brain?

CNS syndrome is associated with high doses of ionizing radiation, particularly when the exposure exceeds a certain threshold that leads to severe damage to the central nervous system. In clinical and radiobiological studies, a dose of 50 Gy is recognized as the level at which significant CNS effects manifest, including neurologic symptoms and increased intracranial pressure due to elevated fluid content in the brain. This occurrence is tied to the detrimental impact of radiation on brain tissue, leading to cell death, edema, and disruption of normal function.

At doses lower than this threshold, while there may be some effects on the brain and nervous system, they typically do not present as acute or severe CNS syndrome. Therefore, understanding that 50 Gy represents a critical dose for CNS effects solidifies it as the correct answer, highlighting the relationship between high radiation doses and severe neurological impairment.