The SI unit of radiation absorbed dose is

Ref Robbins 9/e p428 Gray is a unit that expresses the energy absorbed by the target tissue per unit mass Radiation UNITS Roentgen: Is the measurement of energy produced by Gamma or X-Ray radiation in a cubic centimeter of air. It is abbreted with the capital "R". One milliroentgen, abbreted "mR" is one-thousandth of a roentgen. One microroentgen, abbreted "uR" is one-millionth of a roentgen. RAD: Radiation Absorbed Dose. Original measuring unit for expressing the absorption of all types of ionizing radiation (alpha, beta, gamma, neutrons, etc) into any medium. One rad is equivalent to the absorption of 100 ergs of energy per gram of absorbing tissue. System International (SI) Units The System International (S.I. unit) units for radiation measurements are "gray" (Gy) and "sive" (Sv) for absorbed dose and equivalent dose respectively. The conversion from one system to another is simple: 1 Sv = 100 rem 1 rem = .01 Sv 1 mSv = 100 mR (mrem) 1 mR = .01 mSv 1 Gy = 100 rad 1 rad = .01 Gy 1mGy = 100 mrad 1 mrad = .01 mGy