A cybernetic model for radiation reactions in living cells

A model for radiation reactions in living cells is described. It assumes three different states of the cell. State A is a cell which can grow up to a macrocolony; in state B and C the cell is not able to do so. In state B an 'essential molecule' of the cell has been damaged reparably, in state C irreparably. The sensitivity of the cell is assumed to increase with absorbed dose and to be reduced by recovery reactions in the cell. This can be explained, for example, by indirect radiation reactions with molecules competing with the essential molecule. These competing molecules can be replenished by the cell using an internal energy reservoir. Methods for the experimental determination of all parameters appearing in this model are described. Experiments with stationary diploid yeast cells, irradiated with x-rays, show that the time-constants of recovery and repair are of the same order of magnitude but are dependent on the time interval between or after irradiations, and are dependent on absorbed dose. We expect that this model can be applied also to radiation reactions in other types of cells, and to other ionizing radiations.