Dose and dose-rate effects of ionizing radiation: a discussion in the light of radiological protection

Abstract

The biological effects on humans of low-dose and low-dose-rate exposures to ionizing radiation have always been of major interest. The most recent concept as suggested by the International Commission on Radiological Protection (ICRP) is to extrapolate existing epidemiological data at high doses and dose rates down to low doses and low dose rates relevant to radiological protection, using the so-called dose and dose-rate effectiveness factor (DDREF). The present paper summarizes what was presented and discussed by experts from ICRP and Japan at a dedicated workshop on this topic held in May 2015 in Kyoto, Japan. This paper describes the historical development of the DDREF concept in light of emerging scientific evidence on dose and dose-rate effects, summarizes the conclusions recently drawn by a number of international organizations (e.g., BEIR VII, ICRP, SSK, UNSCEAR, and WHO), mentions current scientific efforts to obtain more data on low-dose and low-dose-rate effects at molecular, cellular, animal and human levels, and discusses future options that could be useful to improve and optimize the DDREF concept for the purpose of radiological protection.

Biological Effectiveness of Ionizing Radiation: Acute vs. Protracted Exposures

“…[52][53][54][55][56], as discussed in [29,50,51,53,57]. This may pertain also to some reports cited in [2,25]. Similar biases might have been active in some studies correlating radiation exposure and minisatellite mutations in the offspring of exposed parents [58,59].…”

“…Conscious or subconscious dose-dependent behavioral changes have probably contributed to the dose-effect correlations found in epidemiological studies: one additional X-ray, endoscopy or blood count can lead to a cancer diagnosis thus influencing statistics. The same mechanism can cause in future an increase in the registered cancer incidence in the high natural background radiation areas (Guarapari, Brazil; Kerala, India; Ramsar, Iran; Yangjiang, China), where no cancer increase has been detected so far [2,[45][46][47][48]; although singular reports on enhanced cancer risk in such areas have already appeared [45,49].…”

“…Several studies were cited in [2] directly [22][23][24] or through the review [25] in support of the no-threshold concept and lowering ISSN: 2471-4879 of the recommended DDREF value down to 1. Some of these papers are discussed below.…”

“…In the author's opinion, the dose-effect relationships with non-neoplastic diseases [30][31][32][33][34] call in question such relationships with cancer, reported e.g. in the studies [23,24,[35][36][37][38][39][40][41][42][43] including those cited in [2,25] in support of the DDREF lowering. Although there may be some risk of cardiovascular disease at high dose and dose-rate exposures [16], existing data are insufficient to confirm a cause-effect relationship between radiation and cardiovascular diseases at doses below 1-2 Gy, while plausible biological mechanisms are unknown [44].…”

“…To adjust the risk estimates at acute exposures to low dose and continuous (low dose rate) exposures, a dose and dose rate effectiveness factor (DDREF) is used [1]. This letter refers to the discussion around re-evaluation of the DDREF value equal to 2, currently recommended by the International Commission on Radiological Protection (ICRP) [2]. The topics of the threshold, hormesis and DDREF are interrelated with the linear no-threshold theory (LNT).…”