Comparison of the effects of various cyclotron-produced fast neutrons on the reproductive capacity of cultured human kidney (T-1) cells

The Inherent Cellular Sensitivity to 62·5 MeV(p→Be+)Neutrons of Human Cells Differing in Photon Sensitivity

The inherent sensitivity of 20 human cell lines to the 62.5 MeV(p----Be+) clinical neutron beam at Clatterbridge, UK, has been assessed and compared to their sensitivity to 4 MeV photons. The survival curves of the cell lines following neutron irradiation were curvilinear, and the inherent neutron sensitivity varied by 4.5 fold (0.1 survival level) between the extreme values, in the cell lines studied. There was a strong correlation between the sensitivity of these human cells to photon and neutron irradiation. It was concluded that should these in vitro patterns occur in the clinic, the 4-fold variation in RBE and inherent sensitivity to neutrons could result in overall lower local control rates following fast neutron therapy than might be anticipated. It suggests the need for the development of predictive assays as a potential means of selecting tumours most appropriate for neutron therapy.

Gamma rays: further evidence for lack of a threshold dose for lethality to human cells

In experiments designed to measure human cell survival sith +/- 2 percent accuracy it was found that low doses (21 to 87 rad) of gamma-rays inactivated the colony-forming ability of cultured human cells with a probability of 0.00226 +/- 0.00012 per rad. There appears to be no threshold for the lethality of radiation to human cells in vitro.