AN ANALYSIS OF THE EQUIVALENT DOSE CALCULATION FOR THE REMAINDER TISSUES

In the 1990 Recommendations of the International Commission on Radiolo gical Protection, the risk-weighted quantity ''effective dose equivale nt'' was replaced by a similar quantity, ''effective dose.'' Among oth er alterations, the selection of the organs and tissues contributing t o the risk-weighted quantity and their respective weighting factors we re changed, including a modified definition of the so-called ''remaind er.'' Close consideration of this latter definition shows that it caus es certain ambiguities and unexpected effects which are dealt with in the following. For several geometries of external photon irradiation, the numerical differences of two possible methods of evaluating the re mainder dose from the doses to ten single organs, namely as arithmetic mean or as mass weighted average, are assessed. It is shown that devi ation from these averaging procedures, as prescribed for those cases w here a remainder organ receives a higher dose than an organ with a spe cified weighting factor, causes discontinuities in the energy dependen ce of the remainder dose and, consequently, also non-additivity of thi s quantity. These problems are discussed, and it is shown that, althou gh the numerical consequences for the calculation of the effective dos e are small, this unsatisfactory situation needs clarification. One ap proach might be to abolish some of the ICRP guidance relating to the a ppropriate tissue weighting factors for the remainder tissues and orga ns and to make other guidance more precise.