The Influence of Wavelength on the Biological Effectiveness of Radiation

Abstract

At the request of the Joint Committee on Radiotherapy the following experiments have been undertaken as a contribution to the study of “the wavelength factor in radiotherapy.” Investigations of the influence of wavelength in determining the biological effectiveness of radiation have given results of a conflicting nature. The extreme claims of a highly selective action of certain wavelengths, made by Moppett17 for X radiation and Reiter20 for ultra-short wireless waves, have now been discredited. But differences of opinion still exist as to the relative effectiveness of soft and hard X radiation and of γ radiation. Packard19 in reviewing the evidence bearing on this problem, has critically analysed the experimental procedures of some workers who claim that the degree of biological response is determined by the quality of radiation used. Variable results by different workers may depend upon:— (a) Differences in the physiological condition of the test material, with concomitant alterations in radio-sensitivity. (b) Differences in the penetration of hard and soft radiation, which implies unequal absorption by unsuitable test objects. (c) Inaccuracies of the physical and biological measurements involved. Anyone acquainted with the literature on this subject will be aware that, even if we consider only those investigations in which these conditions appear to have been fulfilled, there does not emerge from the experimental results, taken together, any clear generalisation as to the relative effectiveness of different qualities of radiation on the various types of organisms and tissues which have been used as test objects.