Equivalent Dose

The equivalent absorbed radiation dose, usually shortened to equivalent dose, or formerly dose equivalent, is a computed average measure of the radiation absorbed by a fixed mass of biological tissue, that attempts to account for the different biological damage potential of different types of ionizing radiation. It is therefore a less fundamental quantity than the total radiation energy absorbed per mass (the absorbed dose), but is a more significant quantity for assessing the health risk of radiation exposure. It is adequate for assessing risk due to external radiation fields that penetrate uniformly through the whole body, but needs further corrections when the field is applied only to part(s) of the body or when it is due to an internal source. A further quantity called effective dose can be calculated if the fractionation of radiation to different parts of the body is known, to take into account the varying sensitivity of different organs to radiation. Another quantity called committed dose is used when the radiation source has entered the body.

Equivalent dose is dimensionally a quantity of energy per unit of mass, and is measured in sieverts or rems.