Typical doses and dose rates in studies pertinent to radiation risk inference at low doses and low dose rates

Abstract

In order to quantify radiation risks at exposure scenarios relevant for radiation protection, often extrapolation of data obtained at high doses and high dose rates down to low doses and low dose rates is needed. Task Group TG91 on ‘Radiation Risk Inference at Low-dose and Low-dose Rate Exposure for Radiological Protection Purposes’ of the International Commission on Radiological Protection is currently reviewing the relevant cellular, animal and human studies that could be used for that purpose. This paper provides an overview of dose rates and doses typically used or present in those studies, and compares them with doses and dose rates typical of those received by the A-bomb survivors in Japan.

Biological effectiveness of very high gamma dose rate and its implication for radiological protection

“…Exemplary HDR values were 0.3 Gy/min (Grosovsky and Little 1985), 0.3 Gy/min (Ueno et al 1982), 0.4 Gy/min (Manesh et al 2014), 0.5 Gy/min (Furuno-Fukushi et al 1988), 0.5 Gy/min (Lorenz et al 1994), 0.5 Gy/min (Nakamura and Okada 1981), 0.70-0.79 Gy/min (Russell et al 1958), and 0.83 Gy/min (Evans et al 1990). These values are much lower than the tens of Gy/min following the atomic bomb detonations in Hiroshima and Nagasaki (Ruhm et al 2018). The results presented in this report suggest that the biological effectiveness of gamma radiation increases when the dose rate reaches ca 8 Gy/min.…”

“…With respect to stochastic effects, the sparing effect of reducing the dose rate below the HDR range is far less clear. This problem is now in the focus of interest, because of discussions regarding the validity of the DDREF (Ruhm et al 2016 , 2018 ). Because epidemiological studies on cohorts exposed to low dose rate radiation are not able to provide a clear answer (Hoel 2018 ), studies have been carried out with animals and in vitro cell systems.…”

“…The dose rate at which the Hiroshima and Nagasaki survivors were exposed to largely exceeded the value of 1 Gy/min. The mix of gamma radiation and neutrons can be divided into five dose components: prompt primary gamma radiation (dose rate between 1.2 × 10 4 and 4.2 × 10 6 Gy/min), prompt neutron radiation (dose rate between 2.4 × 10 3 and 1.4 × 10 6 Gy/min), prompt secondary gamma radiation (dose rate between 10 and 410 Gy/min), delayed gamma radiation (dose rate ca 50 Gy/min), and delayed neutron radiation (dose rate ca 0.1 Gy/min) (Ruhm et al 2018 ). The major contributors to the total absorbed dose were the prompt secondary gamma radiation and the delayed gamma radiation component, where the dose rate was in the order of tens of Gy/min.…”

High CT doses return to the agenda

“…One might argue that the exposure of the atomic bomb survivors is not really relevant here, because cumulated exposure from CT scans is due to low-energy X-rays and might be distributed over several single exposures, while the atomic bomb survivors were exposed to high-energy gamma radiation (plus some contributions from neutrons) and within a single very short period. Indeed, the mean energy of gamma radiation that was present at the bombings of Hiroshima and Nagasaki was of the order of several MeV (Rühm et al 2018a) which is much higher than typical energies of diagnostic X-ray examinations. A recent report of the National Council on Radiation Protection and Measurements (NCRP) has reviewed the biological effectiveness of low-energy photons for evaluating human cancer risk and found that radiation used in X-ray diagnostics might be a factor of about 1.5 more effective than 1.25 MeV gamma radiation emitted by the decay of 60 Co (NCRP 2017).…”

Life-Shortening Effect of Chronic Low-Dose-Rate Irradiation in Calorie-Restricted Mice

“…The accidents at nuclear power plants in Chernobyl and Fukushima resulted in chronic low-dose-rate radiation exposure for a large number of people, although the exposures in Fukushima were much lower than those in Chernobyl (1,2). These incidents motivated essential research to better understand the health effects of such exposure and to develop strategies for alleviating the possible long-term radiation effects.…”