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

Determinations of the relative biological effectiveness of 200-kvep x rays (l.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 Co/sup 60/ gamma rays versus 200-kvcp x rays was found to be 0.86; for 22-Mewp x rays versus 200-kvcp x rays, 0.85; and for 22-Mewp x rays versus Co 0 gamma rays, 1.00. It is pointed out, however, that the quantitative result can be varied by means of the absorbed dose estimates if critical ttssues of different composition, or soft tissue surrounded by bone, are chosen. (auth)