Task Group 91
Radiation Risk Inference at Low-dose and Low-dose Rate Exposure for Radiological Protection Purposes

A Task Group under Committee 1

The detriment-adjusted nominal risk coefficients recommended by ICRP have been based, to a large extent, on data obtained from the atomic bomb survivors in Japan. Because their exposure was a single acute exposure, and because it was thought that the most plausible biological model for the dose response relationship should be linear quadratic (which implies a larger slope at high doses than a low doses), many international and national relevant bodies, such as UNSCEAR, BEIR and also ICRP have used over the years a Dose and Dose-Rate Effectiveness Factor (DDREF) for estimates of these coefficients at low doses. A value of 2 was used by ICRP for low-dose and low-dose rate exposures, which are typical in radiation protection. With more epidemiological information becoming available and with modern techniques of Bayesian analysis, UNSCEAR has recently re-evaluated all the available information using Bayesian techniques and has estimated risk coefficients that are similar to the ICRP estimates using high doses and a DDREF value of 2. However, in their 2006 report the BEIR committee (BEIR VII) also using a Bayesian approach recommended a DDREF of 1.5.

The Task Group will review the currently available information on the estimation of risk coefficients and recommend:

  1. Whether it is desirable to continue to estimate risk at low doses by assessing the slope of the dose response at high doses and then applying a DDREF reduction factor. The alternative is to adopt the UNSCEAR approach of inferring the risk coefficients at low doses by using all available information and techniques of Bayesian analysis for estimating the best expert judgment.
  2. Whether such coefficients are applicable to acute, protracted and prolonged exposure or need a particular correction.

The Task Group will develop a report for publication in the Annals of the ICRP that presents a review of the current science relevant to the estimation of risk at low doses and dose rates, and provides recommendations on how this risk should be estimated for radiological protection purposes.


Members of the Task Group have published a number of papers during the development of the work:

Haley, B., Paunesku, T., Grdina, D.J., Woloschak, G.E. (2015) Animal mortality risk increase following low-LET radiation exposure is not linear-quadratic with dose. PLOS One, 10(12). DOI 10.1371/journal.pone.0140989

Little M.P., et al. (2020) Lifetime mortality risk from cancer and circulatory disease predicted from the Japanese atomic bomb survivor Life Span Study data taking account of dose measurement error. Rad Res 194(3), 259-276

Rühm, W., Woloschak, G.E., Shore, R.E., et. al. (2015) Dose and dose-rate effects of ionizing radiation: a discussion in the light of radiological protection. Radiat Environ Biophys 54(4), 379–401. DOI 10.1007/s00411-015-0613-6

Rühm, W., Azizova, T., Bouffler, S., et. al. (2016) Dose-rate effects in radiation biology and radiation protection. Proceedings of the Third International Symposium on the System of Radiological Protection. Ann. ICRP 45(1S). DOI 10.1177/0146645316629336

Rühm, W., Eidemüller, M., Kaiser, J.C. (2017) Biologically based mechanistic models of radiation-related carcinogenesis applied to epidemiological data. Int J Radiat Biol 93(10), 1093-1117. DOI 10.1080/09553002.2017.1310405

Shore, R., Walsh, L., Azizova, T., Rühm, W. (2017): Risk of solid cancer in low dose-rate radiation epidemiological studies and the dose-rate effectiveness factor. Int J Radiat Biol 93(10), 1064-1078. DOI 10.1080/09553002.2017.1319090

Tran., V., Little, M.P. (2017) Dose and dose rate extrapolation factors for malignant and non-malignant health endpoints after exposure to gamma and neutron radiation. Radiat Environ Biophys 56(4), 299-328. DOI 10.1007/s00411-017-0707-4

Rühm, W., Azizova, T., Bouffler, S., et. al. (2018) Typical doses and dose rates in studies pertinent to radiation risk inference at low doses and low dose rates. Radiat Res 59(S2), ii1-ii10. DOI 10.1093/jrr/rrx093

Wakeford, R., Azizova, T., Dörr, W., Garnier-Laplace, J., Hauptmann, M., Ozasa, K., Rajaraman, P., Sakai, K., Salomaa, S., Sokolnikov, M., Stram, D., Sun, Q., Wojcik, A., Woloschak, G., Bouffler, S., Grosche, B., Kai, M., Little, MP., Shore, R. E., Walsh, L., Rühm, W. (2019) The Dose and dose-rate effectiveness factor (DDREF). Health Phys 116(1), 96-99. DOI 10.1097/HP.0000000000000958

Werner Rhm (Chair), Helmholtz Zentrum Mnchen, Germany
Tamara Azizova (Member), Southern Urals Biophysics Institute, USSR/Russian Federation
Simon Bouffler (Member), PHE, UNITED KINGDOM
Bernd Grosche (Member), ex Federal Office for Radiation Protection (BfS), Germany
Michiaki Kai (Member), Oita University of Nursing and Health Sciences, Japan
Mark P. Little (Member), National Institutes of Health, USA
Kotaro Ozasa (Member), Radiation Effects Research Foundation, Japan
Kazuo Sakai (Member), Tokyo Healthcare University, Japan
Roy E. Shore (Member), New York University School of Medicine, USA
Quanfu Sun (Member), National Institute for Radiological Protection, China
Linda Walsh (Member), University of Zurich, Switzerland
Gayle Woloschak (Member), Northwestern University, USA