An approach towards a unified theory of damage to mammalian cells by ionising radiation for absolute dosimetry

A semi-theoretical model is proposed for quantifying the dominant damage effects of ionising radiation on mammalian cells in vitro with the object of developing a unified theory of radiation action for application in fundamental dosimetry. By comparison with experimental survival fractions reported for 60Co gamma rays, fission neutrons and alpha particle irradiation of mammalian cells, it is demonstrated that the model can cope adequately with dose rate and repair effects. Useful biophysical information can be extracted, for example, on the mean number of double-stranded DNA segments at risk (∼14) upon traversal of the cell nucleus by a single radiation; the time it takes in the cell cycle for damage to become 'fixed' (3-4h); the mean time for a double strand break to repair and the mean lifetime of chemically reactive species. Some unusual predictions are made which are amenable to experimental test. From the information obtained the feasibility of designing the response of dosimetry instrumentation for measurement of absolute biological effectiveness is discussed. (author)