Cell survival at low oxygen tension and dose build-up in argon

Mammalian cells were exposed to 250 kVp X-irradiation in air, argon and nitrogen to determine whether cells irradiated when severely hypoxic have survival curves with lower extrapolation numbers (n) than their aerobic counterparts. Cells irradiated suspended in liquid showed no significant differences between values of 'n' irrespective of the gas used, neither was the sensitivity of cells irradiated in argon any greater than that of cells irradiated in nitrogen. In contrast, cells attached to glass dishes irradiated with the medium withdrawn were apparently much more sensitive in argon than in nitrogen. It has been demonstrated that the lower survival of cells irradiated in argon could have been caused by the greater photoelectric absorption in argon compared with nitrogen. When the dosimetric discrepancy was removed either by absorption of photoelectrons in liquid or by use of high energy radiations, there was no evidence that severe hypoxia during irradiation could lead to reduced values of 'n'.