Radiosensitivity of Selected Sub-lines of a Tumour-cell Population Tested in the Presence or Absence of Oxygen

Abstract
The radiosensitivity of two sub-lines, one hyperdiploid (ELD), the other hypertetraploid (ELT), derived from the same original ascites-tumour cell population, was compared, using two different criteria of radiation injury. Determinations were made in diffusion chambers of either the size of the total cellular content, or the proportion of viable to non-viable cells according to their eosin stainability, at intervals after exposure to single doses of x-rays, in an oxygen or nitrogen atmosphere, covering the range 300–4000 r. After irradiation in a nitrogen atmosphere, the hyperdiploid was found to be more sensitive than the hypertetraploid sub-line. In oxygen, however, no such difference in sensitivity was demonstrated, though the sensitivity of both sub-lines was increased, implying a different oxygen-enhancement for cells of different chromosome content. The authors discuss whether this difference of enhancement could be due to differences between the sub-lines associated with the doubling of the genera, or whether it could indicate that the radiation injury in oxygen is qualitatively as well as quantitatively different from that produced in nitrogen. It is suggested that the presence of oxygen might mask a sensitivity difference demonstrable by radiation exposure under anaerobic conditions.