Cellular response to ionizing radiations: a study of the roles of physics and biology

A study of the complementary roles of physics and biology in determining the response of cellular systems to ionizing radiations has been conducted. Upon exposure to radiation, a cell responds in a binary (yes/no) manner in terms of its proliferative ability (survival). The relationship between the survival probability and absorbed dose may then be examined in terms of relevant physical and biological parameters. The approach to these studies was to vary the physics and biology independently and observe separately their influences upon the measured effect. Unique to these studies was the use of heterogeneous tumor systems. These are solid tumors found to consist of genetically related but identifiably distinct populations of cells. The two heterogeneous systems studied, a murine system consisting of four subpopulations and a human tumor system with two subpopulations, were exposed to graded doses of 14 MeV neutrons or x-rays and their effectiveness in inducing cell lethality compared. A further examination of the radiation effect involved a study at the chemical level, measuring the ability of oxygen to potentiate the damage produced by photon irradiation. To summarize, the physics, biology and the environment have all been varied, and the systematics of the responses studied. The data were analyzed within the formalisms of the dual theory of radiation action, the repair-misrepair model, and the repair saturation model of cell killing. The change in survival curve shape and the increased effectiveness in cell killing for higher Linear Energy Transfer (LET) radiations (neutrons vs. x-rays) are discussed in relation to explanations in terms of either physical or biochemical processes