Radiation induced cancer risk reduction as a function of dose protraction: interspecies comparison

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Ionizing radiation (IR) causes damage to living organisms. The health effects of IR for different total doses and dose rates at which IR was delivered have to be defined by statistical analyses based on whole organism endpoints such as an increase in the risk for development of cancer or an increased risk of life shortening. The factor by which a total dose could be increased, if protracted, for the same final biological effect, is known as dose and dose-rate effectiveness factor (DDREF). The cumulative protracted radiation received by the entire population of USA is very large and falls under regulatory policies that are government defined. These policies rely on the work of national and international agencies evaluating potential dangers of IR using the DDREF value as one of the key input factors for consideration of protracted IR exposures. Ultimately, government regulated limits for occupational and public IR exposures (mostly protracted) and recommendations for X-ray based medical diagnostic procedures (mostly low total doses) all depend on currently accepted DDREF value. Using computational tools and animal data on acute and protracted exposures we found that the DDREF estimate used at this time is inappropriate (Haley et al. 2015) but that dose-rate effectiveness factor (DREF) can be evaluated using extensive animal data. In this project we propose to use interspecies comparisons to refine (1) external beam DREF values and (2) radionuclide dose/quality/route of administration dose rate effectiveness factors (DREF) for specific types of radiation induced cancers (and life shortening from internal emitters). This is especially important in light of the fact that several international bodies are looking to change values for DDREF– a letter from ICRP sent specifically to our group supporting the importance of this work is attached to the application.