On the general validity of linear summation of dose equivalents for mixed radiations

The current definition of dose equivalent for a mixture of radiations used in radiation protection implies some interaction between the radiations. This interaction cannot be derived from the existing biophysical models. A simple concept of interaction is introduced based on the postulate that in the chain of radiation inactivation events, there exists an intermediate stage where different initial lesions, produced by different radiations, become functionally indistinguishable. Hence, they are additive thereafter to produce the same end point observed. It can be shown that the definition of dose equivalent and the definition of average quality factors for mixed radiations can be derived from this concept. Furthermore, this simple concept can be shown to be consistent with many of the published experimental results in radiobiology using mixed radiations. The lesion additivity concept helps to provide both theoretical and experimental support for the otherwise arbitrary definitions of dose equivalent and average quality factor.