Modeling DDREF to understand the risks associated with radiation exposure

Humans are exposed to radiation every day, but the risks associated with this are not fully understood. It is known that ionizing radiation can cause cancer and that the dose and dose rate impact the effect radiation has on human health. To study these effects, data from epidemiological and animal studies are analyzed. The most extensive and commonly used epidemiological study is from atomic bomb survivors in Hiroshima and Nagasaki. All subjects of this study experienced acute exposures, in contrast to the chronic exposure the general population is subjected to every day from sources such as the soil and space. Because of this difference and a lack of statistical power from low dose exposures, the dose and dose rate effectiveness factor (DDREF) is used to extrapolate the risk associated with high dose and dose rate exposures to the risk of low dose and low dose rate exposures. Different research institutions worldwide have worked to quantify the DDREF and estimates range from values below 1 (indicating that acute exposures are safer than chronic exposures) to values closer to 5 (indicating that acute exposures are 5 times more harmful than chronic exposures). Based off of data on dicentric formation, a linear quadratic equation is typically used to fit data. Recently, our lab analyzed life span studies of almost 30,000 mice exposed to various radiation treatment conditions and found that DDREF estimates that extrapolate protracted risks from acute risks are not accurate. Instead, it is best to fit a linear-linear model to data sets with both acute and protracted data. We are currently working to improve our DDREF estimates by using mortality due to cancer. Cancer is the main risk associated with radiation exposure and by narrowing in on more direct causes of death we will better understand new ways to increase human health. This work will improve estimates of risk and influence government policies for the proper level of caution to be taken for protection the general population from radiation exposures.