Absorbed V Equivalent V Effective Dose

The ABSORBED DOSE is defined as the mean energy e imparted by ionizing radiation to matter of mass m in a finite volume V by:

\begin{align} D = \left ( \frac{d \epsilon}{dm} \right ) \end{align}

The SI unit of absorbed dose is $J \over kg$ and its special name is the Gray (Gy).

The EQUIVALENT DOSE HT is defined as:

\begin{equation} H_{T} = W_{R} D_{T,R} \end{equation}


  • $D_{T,R}$ is the absorbed dose delivered by radiation type R averaged over a tissue or organ T;
  • $W_{R}$ is the radiation weighting factor for radiation type R.
  • SI unit of equivalent dose is $J \over kg$ and its special name is the sievert (Sv).

The EFFECTIVE DOSE E is defined as the summation of tissue equivalent doses, each multiplied by the appropriate tissue weighting factor wT, to indicate the combination of different doses to several different tissues

\begin{align} E= \sum W_{T} H_{T} \end{align}

Absorbed dose is a measure of the actual energy deposited in an irradiated mass, while the Equivalent dose adds a measure of biological impact of the radiation type. The Effective dose is an aggregation of per tissue/organ estimates of the Equivalent dose weighted for the sensitivity of the organs involved, giving an estimate of the impact of absorbed dose on an organism.

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