Fig. 2

Linear-quadratic regression analysis of clonogenic survival data obtained from eight human pancreatic cancer cell lines and immortalized human pancreatic ductal epithelial cells. Cells were subjected to colony formation assays upon irradiation at 0-10 Gy. After irradiation, cells were incubated for 14 days, the numbers of colonies with more than 50 cells were counted, and the surviving fractions were calculated. Results of 3–4 independent experiments are depicted in a Trellis plot of the log-transformed survival fraction versus radiation dose with fitted regression curves superimposed (a). Estimated coefficients along with the \(\hat {\alpha }/\hat {\beta }\) ratios for the LQ model (b, c)