ABSTRACT
The conventional method of calculating absorbed dose delivered internally is known as the
medical internal radiation dosimetry (MIRD) scheme (Loevinger et al. 1991). The body is
considered as a set of source organs that have a significant uptake of the radiopharmaceutical,
and a set of target organs that are irradiated by the source organs. It is important to note that
the MIRD definition of target organs is very different from that used in external-beam radio-
therapy (see Section 29.2). For unsealed source therapy, the target organs are any organs (or
tissues) of interest for which the absorbed dose is to be estimated and hence can include normal
tissues (e.g. those at risk) as well as tumours.
