VARIATIONS OF THE RELATIVE SUPERFICIAL AND DEEP BIOLOGICAL EFFECTIVENESS OF RADIATIONS OF DIFFERENT ENERGY

The introduction of high energy radiations has given rise to the complex problem of the evaluation of the relative biological effectiveness of radiatnons of different wave lengths. The lethality on the 30th day was investigated in rats irradiated with radiations of different wave lengths (200 kev x rays and 1.2 Mev gamma rays of Co/sup 60/), in air and during immersion in water (10 cm below the surface). The following results were observed the percent lethality decreases considerably with 200 kev x rays when irradiation in water is substituted for irradiation in air, whereas the decrease is much less notable with Co/sup 60/ gamma rays. This suggests that the biological effectiveness of 200 kev radiations varies considerably according to whether it is measured at the surface or not. The relative biological effectiveness of Co/sup 60/, under the same conditions, also varies, but to a much lesser extent. This different behavior of the relative biological effectiveness of 200 kev radiations and Co/ sup 60/ could be explained by the different phenomena caused by the interaction of radiations and matter superficially and deeply. It seems certain that, of the various factors ln the variability of the relative biological effectiveness, the depth atmore » which the biological reagent considered is situated must be kept in mind. This may prove signiflcant in radiotherapy. (auth)« less