6 RADIATION STANDARDS, INCLUDING FALLOUT ing the fraction of the drug that will be absorbed, can specify the dose to taken which will result in the amountin the body of the patient to produce the desired effect. You see that two kinds of doses are involved here: the dose received by the patient, and the dose actually absorbed by the patient. For convenience, the physician prescribes the dose to be received, although it is the dose absorbed that is important. The situation with radiation is similar to that with drugs. One can and frequently does measure the radiation dose to which a person is exposed. The roentgen is such a unit of exposure dose. Here, as in my analogy, the interest is in the amount of the dose absorbed in the person’s body. With sufficient knowledge of the radiation, one can calculate or estimate the absorbed dose of radiation in various tissues from the exposure dose. (c) The rad: The rad is the unit in which absorbed doses of any kind of radiation are expressed. In most situations the exposure of a person to 1 roentgen of X or y radiation produces an absorbed dose of about 1 rad. (z) The rem: For reasons not clearly understood, smaller absorbed doses of someradiations, e.g., a particles are required to produce the same biological effect as a given absorbed dose of X-rays. In radiation protection as in pharmacology, the important thing is not the exposure dose, or even the absorbed dose, but the effect produced. This and the fact that different types of radiations appear to have quite different biological effectiveness have given rise to the unit of radiation dose, the rem, defined as that dose of any radiation which produces the same biological effect as 1 rad of X-rays. Senator Anperson. When you mention the X-ray, could you express some of these in terms of an ordinary X-ray that a person would have when he had a lung picture made by an X-ray or something of that nature ¢ Could you tell us how many rems that would be? Dr. Wurpepte. I believe a representative figure for good practice in radiology is that a 14 by 17 chest X-ray involves an exposure to the patient of about five-tenths* of a rem. Since the roentgen is about equal to one rad, and the bilogical effectiveness of X-rays is the reference—in other words, relative to X-rays—then the exposure to the patient’s chest will be aboutfive-tenths of a rem. Senator Anperson. Does that continue with each X-ray? Supposing the patient is having a chest X-ray once a month; is this repetitive? Dr. Wurrrte. Yes, certainly to a first approximation of our understandimg. I am not sure whether you are going to get recovery from this. In other words, if you go the other direction and say instead of giving him one a monthfor 20 years I give him the same exposure all on the same day, then the biological effectiveness of a large dose in a short time is much greater than that from the same dose spread over months or years. Is that the point? Senator Anperson. No. I went out to the Southwest for tuberculosis treatment and had an X-ray picture of my chest once a month for ® years. People worry about what is going to happen when these tests are made in the Pacific area. Am I going to get more radiation from the highaltitude test that is going to be madeor that was made 1A better estimate for modern practice is five-hundredths (0.05) of a rem. eo tyte . Bg ee ey en ae Bab ap Te a ae Sy at PRURRARRSSERBEISYaSheARERRESFRRRES e