A, Representative images and bar graphs showing that calcitriol treatment (vehicle or 0.1, 1, 10, and 100 nM) decreased the spheroid forming abilities of TICs in a dose dependent manner (n = 3; ** P < 0.01 and *** P < 0.001 as compared to the control). B, Calcitriol treatment (at 1 nM) in primary culture reduced the spheroid formation in secondary culture (n = 3; *** P < 0.001 as compared to white bar and + P < 0.001 as compared to dotted bar). C, Analysis of combined treatment of TICs with calcitriol (10 nM) and 2 Gy of ionizing radiation (n = 3; P < 0.05). Values represent mean ± SEM.