The excess risk for solid tumor formation in survivors of Nagasaki and Hiroshima bombings follows a dose response curve best described by a linear or linear-quadratic function. There is no statistically significant advantage to using the more complex linear-quadratic expression for estimating solid tumor risk. For leukemia data, however, a linear quadratic model is most appropriate.

Only the linear and linear-quadratic functions are currently recognized by major risk assessment and management agencies. The figure below summarizes all potential functions offered to explain low dose exposures and cancer risk.