Fig. 5.

The effect of dose-fractionation on predicted excess relative cancer risk (ERR): as the same total radiation dose is split into fractions (one fraction per day, with gaps on weekends), thereby protracting it over a longer time, cancer risk predicted by the model increases. This occurs because cell repopulation during prolonged exposure partially compensates for cell killing by radiation. The doses refer to a given organ, such as the lungs or female breast, and not to whole body exposures. The following parameter values were used: b = 0.25 y⁻¹, X = 10.0 y × Gy⁻¹, Y = 0.5 Gy⁻¹, δ = 0.01 y⁻¹, Z = 10.0 cells/niche, α = 0.3 Gy⁻¹, β = 0.0 Gy⁻², λ = 0.35 day⁻¹, T _x = 30 y, T _y = 0.0 y, and L = 10 y