Differences in radiation sensitivity in subpopulations of mammalian multicellular systems

A partial review of a new and existing data on the radiation sensitivity of complex cellular systems of mammals is reported. The experimental evidence suggests that a unique sensitivity can always be associated with each subpopulation in a complex system, provided that such a subpopulation can be adequately identified and monitored. The analysis of the survival curves of normal tissues confirms the variations in radiation sensitivity between different renewing tissues. In particular, the hemopoietic system is most responsive to radiation and, at the same time, represents a good example of how the radiation sensitivity of an overall population can be resolved for subpopulations of varying degrees of commitment to proliferate and differentiate. Moreover, variations in radiation response depending on the redistribution of cells along the cycle phases have been taken into consideration, mainly by analyzing the results in different tissues of fractionation experiments at relatively high and low doses. These phenomena are discussed for both normal and malignant systems