Database of Radiogenic Cancer in Experimental Animals Exposed to Low Doses of Ionizing Radiation

Abstract

For decades, there have been debates regarding the nature of the relationship between exposure to low doses of ionizing radiation and cancer risk. Under the linear no-threshold hypothesis, which serves as a theoretical basis for current radiation protection standards, the risk of cancer at low levels of exposure is presumed to be directly proportional to dose. Opponents of this hypothesis claim that there are threshold doses for radiation carcinogenesis, or even a reduction in cancer risk at low doses (a phenomenon referred to as “radiation hormesis”). Epidemiological, animal, molecular, and cellular studies were conducted to resolve this controversy, although each of these study types has its strengths and limitations. Although the results of animal experiments are not directly applicable to humans, data can substantially add to our knowledge on the form of relationship between radiation dose and cancer risk in a wide range of doses. Laboratory animals are a homogeneous population with little biological variability; animal experiments are conducted under controlled conditions with good estimates of radiation doses. In order to address the question of whether or not the dose-response curve for radiation carcinogens is linear at low doses, a comprehensive database of animal carcinogenesis experiments was assembled involving exposure to different types of ionizing gradation. The database includes virtually all publicly accessible data on the induction of radiogenic cancer in laboratory mammals. This review provides a descriptive overview of the experiments included in the database, along with a qualitative assessment of the shape of the dose-response relationship for radiation carcinogenesis at low doses in experimental animals.

Acknowledgments

Support for project was provided by Électricité de France, the Department of Energy (USA), the Central Research Institute of Electric Power Industry (CREIPI, Japan), COGEMA Resources, Inc. (now AREVA, Canada), MDS Nordion, the Canadian Nuclear Society, and the CANDU Owners Group to the International Centre for Low Dose Radiation Research at the University of Ottawa. Additional support was provided by Health Canada to the McLaughlin Centre for Population Health Risk Assessment at the University of Ottawa. D. Krewski is the NSERC/SSHRC/McLaughlin Chair in Population Health Risk Assessment at the University of Ottawa. We are grateful to Benaceur Assif, Dianne Murray, Jacques Deslauriers, and Russell Renaud for their assistance in the preparation of the database described in this article.