The Lethal Dose of Total-Body X-Ray Irradiation in Swine

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Abstract
The Development of the atomic bomb has stimulated great interest in the study of ionizing radiation injury to living tissue. A large field experiment, designed to determine both physical and biological effects of the release of atomic energy, was successfully carried out by Joint Task Force One in Operation Crossroads in the summer of 1946 (1, 2). It is desirable to produce comparable ionizing radiation lesions in laboratory experiments not only to allow correlation with and better understanding of the data obtained at Bikini, but also to serve as a basis for future studies of ionizing radiation injuries. Previous work has largely concerned smaller forms. Some interest lies in studying larger animals, such as swine, not only from the standpoint of greater tissue masses and the increasing significance of depth dosage, but also because of a possible doser relation to the radiosensitivity of man. Groups of swine were given known amounts of total body irradiation with hard x-rays emanating from an industrial x-ray tube under as nearly identical conditions as possible. This report concerns the first phase of the laboratory studies, namely, the amount of radiation administered to the whole body (to each lateral aspect in succession) necessary to kill, during a period of 30 days, 50 per cent of the animals exposed (LD 50/30). Subsequent reports will describe the pathologic and hematologic findings. Materials and Methods The x-ray generator used was a 1,000-kv., 3-ma. General Electric Industrial x-ray unit which produced both a transmitted and an angular beam. Due to the limited area covered by the transmitted beam, it was blocked off with lead plates, and the animals were exposed to radiations from the angular beam only (Fig. 1). At a given elevation the angular beam produced radiations of similar quality and quantity in an arc of 360° around the tube. In order to obtain maximum efficiency and to avoid large differences in doses in different parts of the horizontal area occupied by the animals during the test, only that portion of the angular beam was used that fell between 95 and 135° from the vertical (Figs. 1 and 2).

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