A metric unit of the amount of radiation absorbed by biological material.
One sievert (Sv) equals 1 joule (J) of energy absorbed per kilogram of matter (1 J/kg) and is adjusted for the type of biological material that is affected. For human tissues, 1 Sv equals 1 gray (Gy). There are 1000 millisieverts (mSv) in 1 sievert (Sv).
Radiation therapy doses may be described by the number of millisieverts (mSv) to be delivered during each treatment.