neeeneee ae ee 326 RADIATION STANDARDS, INCLUDING FALLOUT The 1957 hearings introduced the argument concerning proportionality or linearity in dose-effect relationships and of the existence of a threshold for radiation effects. Dr. Brues’ testimony in 1959 carried forward the argument and presented data from studies done on man, notably those of Dr. Alice Stewart, of Oxford University, those done on small experimental animals,especially those of Dr. R. H. Mole, of England, and of Dr. Arthur Upton, of the Oak Ridge National Laboratory. This subcommittee has been belabored over the years with evidence and arguments for and against the presence of a threshold and proportionality. The paper submitted in the 1959 hearings by Dr. Brues, “Critique of the Linear Theory of Carcinogenesis,” summarizes succinctly the viewpoint of many. Have data been developed during the past 3 years from human sources which may shed more light on the area of somatic effects, especially proportionality and threshold? I wish I could say today that I am able to present data which would ease the lot of this sub- committee and of all committees and persons concerned with the longrange effects of ionizing radiation delivered at low-dose rate over long periodsof time. During the past 3 years no data have accumulated, which could strengthen convictions concerning the presence or absence of proportionality and threshold. We must again state as was stated in the 1959 summary of the hearings— and here again, it was pointed out, no experiments aimed at observing these biological effects have ever been conducted at radiation levels very close to natural background. As before, all conclusions based on experimental or clinical data use data obtained at higher radiation levels. Let us now review some of the recent developments in the field. The work of Dr. Alice Stewart in England, and discussed in 1959, suggested that children who received whole body radiation in the range of 1 to 10 roentgens before birth, while the mother was receiving X-rays to the abdomen for pelvic measurements, and so forth, had about. twice the incidence of cancer or leukemia than did children whose mothers were presumed to have received no abdominal irradiation during pregnancy. Specifically, Stewart’s group found a higher frequency (13.7 percent) of diagnostic X-ray abdominal exposures in mothers of children dying from cancer than in mothers of control children (7.2 percent). Four similar retrospective studies have been carried out in this country. One of these is in line with the observations of Stewart and others. Three other studies do not bear out these observations. Of prime importance in retrospective studies is the choice of the control group. This has varied for the most part, in all of these studies done retrospectively, nor do they differentiate clearly between the apparent increased incidence of leukemia and (a) the effects of ionizing radiation and (b) the effect of the medical conditions which prompted the original abdominal X-ray examination of the mother, or of other diseases of the mother occurring during the pregnancy. An extensive and important prospective study of the incidence of leukemia in children irradiated in utero during the course of abdominal or pelvic X-ray examination of the mother was published by Court Brown, Doll & Hill, in 1960. set eRepeneee