Towards a new dose and dose-rate effectiveness factor (DDREF)? Some comments

The aim of this article is to offer a broader, mechanism-based, analytical tool than that used by (Rühm et al 2016 Ann. ICRP 45 262-79) for the interpretation of cancer induction relationships. The article explains the limitations of this broader analytical tool and the implications of its use in view of the publications by Leuraud et al 2015 (Lancet Haematol. 2 e276-81) and Richardson et al 2015 (Br. Med. J. 351 h5359). The publication by Rühm et al 2016 (Ann. ICRP 45 262-79), which is clearly work in progress, reviews the current status of the dose and dose-rate effectiveness factor (DDREF) as recommended by the ICRP. It also considers the issues which might influence a reassessment of both the value of the DDREF as well as its application in radiological protection. In this article, the problem is approached from a different perspective and starts by commenting on the limited scientific data used by Rühm et al 2016 (Ann. ICRP 45 262-79) to develop their analysis which ultimately leads them to use a linear-quadratic dose effect relationship to fit solid cancer mortality data from the Japanese life span study of atomic bomb survivors. The approach taken here includes more data on the induction of DNA double strand breaks and, using experimental data taken from the literature, directly relates the breaks to cell killing, chromosomal aberrations and somatic mutations. The relationships are expanded to describe the induction of cancer as arising from radiation induced cytological damage coupled to cell killing since the cancer mutated cell has to survive to express its malignant nature. Equations are derived for the induction of cancer after both acute and chronic exposure to sparsely ionising radiation. The equations are fitted to the induction of cancer in mice to illustrate a dose effect relationship over the total dose range. The 'DDREF' derived from the two equations varies with dose and the DDREF concept is called into question. Although the equation for acute exposure can be used to analyse atomic bomb survivor data, the fitting is dominated by the quadratic dose component. Thus, little useful information can be derived about the linear dose component which is important for the derivation of low dose rate risk. The ICRP are advised to derive the risk at low dose rates from epidemiological studies of, for example, worker populations, together with information from cellular radiation biological research.