The "Synergistic" Action of Mixed Irradiation with High-LET and Low-LET Radiation

Abstract

The combined modalities of various agents such as radiation, chemicals and physical agents are often used, and exposure to mixture of agents sometimes occurs in nature. However, it is not clear whether these combined effects are synergistic, partly because definition of the term {open_quotes}synergism{close_quotes} is confusing, as pointed out by Streffer and Mueller. It is, of course, desirable that the definition should be simple and widely applicable to all agents. Yet the underlying mechanisms of the effects of different agents are probably different, and the mechanisms of combined effects are different and more complicated than those of a single agent. It is therefore important to define synergism taking each underlying mechanism into consideration. From this viewpoint, the definitions of synergism which have been used to date are examined with respect to the effect of a mixture of different types of radiation on cells, and they are shown to be inappropriate and misleading. This is probably attributable to simply treating the resulting phenomena (cell survival in most cases) without adequately taking into consideration the knowledge of underlying biological mechanisms in defining the synergism that may occur with irradiation. This commentary discusses the inappropriateness of current definitions and proposes a new definitionmore » in terms of biological mechanisms as a counterproposal. 16 refs., 6 figs.« less