PNNL

Abstract

The conventional paradigm in radiation biology has been that DNA is the primary target for energy deposition following exposure to ionizing radiation. However, studies focusing on the non-target effects of radiation, i.e. effects occurring in cells not directly exposed to radiation, imply that the target of exposure is larger than what has traditionally been assumed and could have significant implications for radiation health risks. We have conducted an extensive study of the low-LET bystander effect including multiple cell lines and endpoints and various radiation sources and exposure scenarios. In no instance do we see evidence of a low-LET induced bystander effect. However, direct comparison for alpha particle exposure showed a statistically significant media transfer bystander effect for high-LET but not for low-LET radiation. From our results it is evident that there are many confounding factors mitigating bystander responses as reported in the literature and for the cell lines we studied that there is a LET dependence for the observed responses. Our observations reflect the inherent variability in biological systems and the difficulties in extrapolating from in vitro models to radiation risks in humans.