Classical radiation biology dogma, bystander effects and paradigm shifts

A classical dogma of radiation biology asserts that all effects of radiation on cells are due to it's direct, immediate actions. But evidence accumulated over the last 50 years shows that radiation also has, indirect 'non-target' actions including 'bystander' effects in which effects of radiation on cells or media are transported to cells or tissues that were not 'hit' by the radiation, leading to changes in their function. This important but heretical recognition of radiation actions has been referred to, probably incorrectly, as a 'paradigm shift.' What these signals are and how they induce changes is not well understood. Also not clear is how, or if, bystander effects might affect risk estimates for exposure to low doses of radiation. These issues are reviewed and explored in this series of papers.