Figure 1. Photon irradiation of CAL33 cells in the aluminium hypoxic chamber.

Culture flasks were arranged in three levels, separated by lead plates (thickness 1.31 cm; distance 6.5 cm). Thus, irradiation doses were reduced by half (D₁, D_1/2, D_1/4), respectively, as confirmed by dosimetric measurements. Cells were irradiated with three different doses in one irradiation experiment. Hypoxia was established by repeated aspiration of air and influx of 95% N₂, 5% CO₂.