High Quality Content by WIKIPEDIA articles! The roentgen equivalent in man (or mammal:579) (abbreviated rem; symbol rem, or often but incorrectly R) is a deprecated CGS unit of equivalent dose, effective dose, and committed dose. Quantities measured in rem are designed to represent the stochastic biological effects of ionizing radiation, primarily radiation-induced cancer. These quantities are a complex weighted average of absorbed dose, which is a clear physical quantity measured in rads. There is no universally applicable conversion constant from rad to rem.