Effective dose and equivalent dose:
It is important to distinguish between two types of absorbed doses, depending on the type of radiation involved. When the entire body is exposed, as is the case with sources external to the body, exposure is measured in terms of the ‘effective dose’ – the global dose absorbed by the body. By contrast, when the exposure is limited to a specific organ (as it occurs in therapy or, say, an accident), the relevant dose is the ‘equivalent dose’, which is calculated by taking the amount of energy absorbed locally and the nature of the radiation into account.
Léonard de Vinci : Homme de Vitruve