The quality of ionising radiations emitted by radionuclides incorporated into mammalian cells

Survival data, from the literature, for 125I, 77Br, 3H and 131I have been re-analysed to extract cross sections for inactivation, by the slowing down charged particle fluence. When comparison is made with results similarly expressed for external irradiation with heavy particle and photon beams, the qualities of the low-energy emitters 125I, 77Br and 3H are found to approach those for heavy particles. An explanation for the damage mechanism is sought in a recently developed model for radiation action. Results are consistent with the interpretation that electron damage is caused predominantly at the end of the tracks, and the actual incorporation simply ensures the slowing down fluence of low-energy tracks interacts preferentially in the vicinity of radiosensitive sites. The absolute biological effectiveness of these radiations can be expressed quantitatively in terms of the model parameters. (author)