ABSTRACT
This chapter considers a number of factors both physical and biological which can affect the way a cell responds to radiation, with particular emphasis on whether or it survives. Theories of cell inactivation developed naturally from the recognition of the stochastic nature of energy absorption in biological material. The best known is the so-called target theory. The dose delivered can clearly be expressed in terms of the number of inactivating events or “hits” per unit volume produced randomly through the irradiated material. Formal target theory has thus offered a framework in which to try and interpret the shapes of survival curves in biophysical terms. In certain restricted situations, the theory has allowed calculations of target volumes and molecular weights to be made. The general validity of the theory of dual radiation action has recently been questioned as a result of experiments with ultrasoft X-rays, which produce tracks much shorter than this interaction distance.
