risk side of the bene t–risk equation?

Abstract. expected increase in biological eVectiveness of these The potential radiation hazards associated with routine screening lower-energy X-rays is that they set in motion slower mammography, in terms of breast cancer induction, are discussed secondary electrons, with correspondingly higher in the context of the potential bene ts. The very low energy LET (Brenner and Amols 1989, Kellerer 2002).X-rays used in screening mammography (26–30 kVp) are In this regard, Frankenberg et al. (2002) reportedexpected to be more hazardous, per unit dose, than high-energy data on in vitro oncogenic transformations frequenciesX- or c-rays, such as those to which A-bomb survivors (from which radiation risk estimates are derived) were exposed. Based induced by 29-kVp X-rays relative to ‘conventional’ on in vitro studies using oncogenic transformation and chromo- 200-kVp X-rays suggesting that the low-energy X-rays some aberration end-points, as well as theoretical estimates, it used in screening mammography are considerably seems likely that low doses of low-energy X-rays produce an more biologically eVective. This conclusion echoesincreased risk per unit dose (compared with high energy photons) some earlier calculations on this subject (Brenner andof about a factor of 2. Because of the low doses involved in Amols 1989) and a variety of earlier experimentalscreening mammography, the bene t–risk ratio for older women would still be expected to be large, though for younger women data for chromosome aberration induction (see below). the increase in the estimated radiation risk suggests a somewhat An increase in the relative biological eVectiveness later age than currently recommended—by about 5–10 years — (RBE) of low-energy mammographic X-rays com-at which to commence routine breast screening