Fig. 4

Discovery of a linear quadratic response of lung tissue to whole thoracic irradiation. The LQ-model was applied to fit the in-vivo lung tolerance data, i.e., the degree of fibrosis development determined by FIs after single vs. fractionated irradiation. The negative log10 transformed FI values are plotted as a function of the total prescribed doses. The LQ parameters were derived as: α = 0.048 Gy⁻¹, β = 0.010 Gy⁻², α/β = 4.800 Gy for single fraction; α = 0.015 Gy⁻¹, β = 0.0038 Gy⁻², α/β = 3.947 Gy for five fractions. Single fraction photon doses are shown as solid circles and 5 fractionated as solid squares