Comparisons of Cellular Radiation Response Using Absolute Rather Than Relative Parameters

One important goal of radiobiology is to describe the response to radiation damage in quantitative terms. Because the dose response is nonlinear, this typically involves the comparison of several dose-dependent parameters. Past attempts at simplifying this process have often involved manipulations of these dose-dependent parameters to derive a single comparative number. Unfortunately, the advantages of a single comparative number, often a ratio or even a ratio of ratios, can be outweighed by the loss of significant biological information. Examples are given in four areas of research: (1) definition of radiation response at clinically relevant radiation doses, (2) modification of radiation sensitivity by oxygen, (3) effects of combined radiation modifiers (e.g., sensitizers and protectors), and (4) comparisons of radiation modifiers in different dose/response regions. In each area, to define and compare dose response, we propose the use of consistent, simple, and absolute radiation response parameters: the inverse dose (or dose) required to produce a given effect. The use of absolute sensitivity (or resistance) avoids the use of many other parameters, ratios, and definitions and permits a uniform and unambiguous description of "radiation response."