Comparative Effectiveness of Several X-Ray Qualities for Acute Lethality in Mice and Rabbits

Early studies of the relative effectiveness of different qualities of ionizing radiation, reviewed by Packard (1), were chiefly concerned with the effect of X-rays of therapeutic quality on small biological test objects. A more recent review by Zirkle (2) has summarized biological studies that have used a broad range of radiation qualities in an effort to correlate response to the energy transfer involved. Acute radiation death in mammals has not been widely employed as a criterion of relative effectiveness of X-rays in the therapeutic range. Potter (3) demonstrated a relationship between exit dose and lethality in rats with 100and 400-kvp X-rays wherein equal effect was noted when the exit doses were similar for compared qualities. A like relationship was observed by Ellinger et al. (4) for the exit dose and LDso in mice exposed to 140and 200-kvp X-rays. The implication that nonuniformity of depth dose can account for variation in effectiveness of X-rays has not been well established. Thus, the present study examines the relationship of acute lethality and depth-dose distribution in mice and rabbits exposed to X-rays ranging from 80 to 250 kvp.