The effect of fractionated irradiation on senescence induction of non-tumorigenic cells and CICs. After radiation treatment cells were fixed and stained for β-galactosidase activity. (A) Representative pictures of cells after fractionated radiation regimen and β-gal assay. White arrow: quiescent non-tumorigenic cells; red arrow: non-quiescent CICs; red star: quiescent CICs. (B) Bar graphs show quantification of senescent cells in T47D. Red bars: total population; blue bars: non-tumorigenic cells; green bars: CICs. Means (+/- SEM) of at least two independent experiments are shown.