Risks from low levels of radiation are generally assessed with the Linear No Threshold (LNT) theory. This theory states that the risks of cancer are in direct proportion to the amount of exposure, even for very small exposures. This methodology of risk assessment is supported by a series of reports called the BEIR reports: Biological Effects of Ionizing Radiation. BEIR I through BEIR VII....
Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), through a combination of time-lapse live imaging and mathematical modelling of a special line of human breast cells, have found evidence to suggest that for low dose levels of ionizing radiation, cancer risks may not be directly proportional to dose. This contradicts the standard model for predicting biological damage from ionizing radiation – the linear-no-threshold hypothesis or LNT – which holds that risk is directly proportional to dose at all levels of irradiation.
The research is analogous to pointing out that: BEIR says that if 100 aspirins taken at once is lethal, and 100 men each take one aspirin apiece--one of those men is going to die. That would be a linear response to low dosage aspirin consumption.
Now where does this leave the Japanese Government's decision to the evacuation of the entire population of an exclusion zone, when: Fourteen elderly Japanese died during the evacuation, as a direct result of their bus trips, problems with IVs and hydration, etc..
More to the point, was their decision driven by the outlandish rantings of anti-nuclear campaigners - if so, both groups should acknowledge direct responsibility for those deaths.