The Relative Biological Effectiveness of 22-Mevp X-Rays, Cobalt-60 Gamma Rays, and 200-Kvcp X-Rays: III. Determined by Acute Lethality in Rats

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Abstract
Deter-minations of relative biological effectiveness RBE of 200-kvcp X-rays (1.4 mm Cu HVL), Co60 [gamma] -rays, and 22-Mevp X-rays from a betatron were made by using survival of Sprague-Dawley rats as the criterion of effect, and estimating the absorbed dose to the soft tissue of the animals. Six simultaneous experiments were carried out at a dose rate of 40 rads/min. The RBE for Co60 [gamma]-rays versus 200-kvcp X-rays was 0.86; for 22-Mevp X-rays versus 200-kvcp X-rays, 0.85; and for 22-Mevp X-rays versus Co60 -rays, 1.00. The quantitative result can be varied (by means of the absorbed dose estimate) if critical tissues of different composition, or soft tissue surrounded by bone, are chosen.