The relevance of dose for low-energy beta emitters

Abstract

Specific issues in risk assessment for low-energy beta emitters include specification of theradiation weighting factor, values of relative biological effectiveness for specific or accuraterisk estimates, non-uniformities of dose within tissues and cells, and use of standard tissueweighting factors for non-uniform situations. Unusual features of low-energy beta emittersinclude: increased average ionisation density on subcellular (and cellular) scales; shortranges of the beta electrons; non-uniformity of the absorbed dose over subcellular, cellular,and tissue dimensions; reduced hit frequencies; nuclear transmutations; different chemicalforms, influencing biokinetics and dose distributions; and large isotopic massdifferences, particularly in the case of tritium and hydrogen. Many of these features arenot included explicitly in conventional radiation protection dosimetry, althoughthey may be partly included in experimental determinations of relative biologicaleffectiveness. Theoretical and experimental studies have shown low-energy electrons to beparticularly efficient in producing double-strand breaks in DNA, including complexdouble-strand breaks. Hence, on fundamental grounds, tritium beta particles should beexpected to have greater biological effectiveness per unit absorbed dose than 60Co gamma-rays or orthovoltage x-rays. For practical purposes, and in view of the paucity ofepidemiological estimates of risk from low-energy electrons, consideration should begiven to applying a raised relative biological effectiveness, say of value 2, to alllow-energy internal emitters, including beta particles and soft x-ray emissions.