Actually, it has been shown in the last 10 years that the cellular response to ionizing radiation deviates from the "linear quadratic" (a strange term indeed) model at very low doses. There is a dose threshold below which it is actually more damaging than previously predicted. The theory goes that at very small doses the cell's repair mechanisms aren't triggered. There's a fairly recent review article by the guys who discovered the phenomenon here: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd= Retrieve&db=pubmed&dopt=Abstract&list_uids=1498249 0&query_hl=1&itool=pubmed_docsum Bear in mind that this is IONIZING radiation, so it is a totally different animal, but it is important to note that extrapolation/interpolation doesn't always give you the right answer. So personally, I would view cancer incidence data from low doses as very suspect at this point.