Quality Factor, Concepts and Issues

Abstract

Abstract Three issues in quality factor assignment arise from Report 40 of the ICRU. These include the validity of the observation of high RBE values for high-LET radiation at low doses, the question of reference radiation, X or ? rays, and the 'effective' quality factor in the body compared with the nominal value of Q. On the first item, high values of RBE at low doses are becoming generally accepted, see a recent report from the NCRP. On the second, a survey of past recommendations of both ICRP and NCRP indicate that both organisations have, for protection purposes, always set all low-LET radiations equal to 1 and accepted the differences (of 2-3 times) between them. However, for radiobiological purposes high energy ? rays are to be preferred as the reference radiation. Third, the 'effective quality factor' or radiation weighting factor, WR, for a variety of whole body exposure circumstances can be estimated from HE = WR S wTDT where the effective dose equivalent is the summation of tissue weighting factors wT, times the absorbed dose DT for the organ, multiplied by an average 'radiation weighting factor' WR. WR values can be calculated for a variety of exposure circumstances and are always less than Q. Maximum values, for fission neutrons for example, are not greatly less however. These issues are under further consideration by the ICRP.