ORRISK completed a study for The National Institute for Occupational Safety and Health (NIOSH) to re-evaluate dose and dose-rate effectiveness factors (DDREFs) for low-LET radiation (photons and electrons) that are incorporated in cancer risk models in the Interactive RadioEpidemiological Program (IREP). The objective of this study was to develop recommendations that provide unbiased representations of the current state of knowledge of DDREFs for low-LET radiation. 

This study evaluated the scientific basis for developing DDREFs and proposed probability distributions of DDREFs for solid cancers in IREP. More generally, our intent was to develop a probability distribution of a DDREF for solid cancers that could be used in any cancer risk assessments that account for uncertainty. We also evaluated the adequacy of the LQ dose-response model for all leukemias (excluding CLL) and specific types of leukemia in IREP and application of the LQ model to chronic as well as acute exposures. This study involved a comprehensive review of microdosimetric, radiobiological, and epidemiological data on low-dose and low-dose-rate extrapolations of cancer risks associated with exposure to low-LET radiation. 

As part of this study, data on radiation dose-responses in cells and laboratory animals that might be relevant to estimating DDREFs for cancer in humans were evaluated. These include:

  • Genetic and cytogenetic data
  • Cancer induction in animals
  • Life shortening in animals

Radioepidemiological data on several types of solid cancers and leukemias in humans can be used to estimate DDREFs. In this study, we evaluated data on dose-responses for all solid cancers as a group (incidence and mortality), female breast cancer (incidence and mortality), thyroid cancer (incidence), lung cancer (incidence and mortality), skin cancers (incidence), and leukemias (incidence and mortality).

Dependence of Cancer Risk on Dose and Dose Rate of Low-LET Radiation         [6 MB (394 pages)]

Dose and Dose Rate Effectiveness Factor