Median lethal dose definition
median lethal dose (LD 50) the quantity of an agent that will kill 50 per cent of the test subjects; in radiology, the amount of radiation that will kill, within a specified period, 50 per cent of individuals in a large group or population.ee also median effective dose. erythema dose that amount of radiation that, when applied to the skin, causes erythema (temporary reddening). fatal dose lethal dose.