RADIATION STANDARDS, INCLUDING FALLOUT 329 range—with our three malignancies—we have a probability of about 1.34 times 10%. Now let us make the usual worst assumption; namely, that the relationship at all dose levels is linear and that there is no threshold and let us extrapolate points at the lower body contents; namely, at 0.01 to 0.1 microcurie and at 0.001 to 0.01 microcurie. It can be seen that we would needat least 140 cases with 36 years’ irradiation in order to just see one tumor above the natural incidence. We have 102 persons in this group. We would need at least 1,500 cases to see one tumorat 0.001-0.01 microcurie. We have only 36 cases in this group. From the number of persons available for study in the United States by the three groups it may be possible to add one more point at the 0.01 to 0.1 microcurie range. There are probably not enough persons available in the world who carry a body burden of radium at the 0.001 to 0.01 microcurie range to make possible a determination of this point on our dose-malignant effects chart. However, these studies may lend confidence in the permissible body burden for radium at the occupationallevel. They may at some time in the future makeit possible to add another point on the chart at one order of magnitude below the occupational level of 0.1 microcurie. These studies represent the largest body of data on the long-term effects of bone-seeking radioelements in man. The number of persons available for study who carry a significant body burden of radium—thatis, between 0.001 and 0.1 microcurie—is so small in relation to the numbernecessary to see one tumor above the natural incidence—making the most pessimistic assumptions concerning radiation tumorigenesis—that it would seem impossible to derive from these studies meaningful estimates of the risk of tumor induction in the human from the other bone-seeking radioelements, notably Sr”, at levels of Sr® present today in our skeletons and anticipated from future weaponstests. What other human data exist which might aid in our understanding of radiation-induced neoplasia? Several studies have been carried out and others are now underway on the relationship of irradiation of the mediastinal structures in childhood and the subsequent clevelopment of leukemia and other tumors. Some investigators have found an increased incidence of leukemia in children given radiation to the thymic area whereas others have not. Of prime importance, but infinite difficulty, is the selection of a satisfactory control group. The studies of Simpson and Hempelmann and others would indicate an increased incidence of both leukemia and other malignancies in 2,393 such treated children. Most of the other excess malignancies were of the thyroid gland and occurred in children given 200 roentgens or more. Unfortunately, this study cannot as yet, differentiate between the association of leukemia and either thymic enlargement or exposure to X-rays. Other studies fail to demonstrate an increased incidence of leukemia in these irradiated children, although several studies showed an increasedincidence of thyroid neoplasia. These data, while suggestive of heightened radiosensitivity of the thyroid for tumor induction in early life, are at present inadequate for the purposes of either establishing the presence or absence of a threshold or linearity of response. Moreover, the comparison of fallout raclioiodineirradiation of the thyroid of children with the response noted in these clinical studies cannot be made. In the case of radio- ih lakes ed aS orese oye are crc eee neha ag BEEFe geht aetbthctetababeheheheh gta cAnaaad anesraeigRE