Genetically Significant Dose to the United States Population from Diagnostic Medical Roentgenology, 1964

Abstract

Genetically significant dose (GSD) is an index of radiation received by the genetic pool, which determines the progeny of a given population. The annual GSD is obtained by weighting the individual gonad doses received during x-ray examinations by the number of individuals examined and by the relative contribution of those persons to the expected number of future children to be produced by the population. It is expected that this dose, if received by every member of the population, would result in the same total genetic effect to the population as the doses which are in fact received by individuals within the population (1). Expressed symbolically (2): where: Di = the average gonad dose for a specified type of examination for a patient in age-sex class (i); ni = the number of persons in age-sex class (i) who had the specified type of examination during a year; Pi = the expected number of future children to an individual in age-sex class (i) Ni = the number of persons in age-sex class (i) in the total population. In order to calculate genetically significant dose, average gonad doses for each type of examination shown in Table I were calculated separately for males and females in each of the age groups: under 15 years, 15 to 29 years, 30 to 44 years, 45 to 49 years (females) and 45 to 64 years (males). Data on the number of persons in each of these age-sex groups who had the specified type of examination were tabulated from reports of examinations in the x-ray exposure study (3). The expected numbers of future children were derived by assuming the continued operation of observed age-specific birth rates by age of mother and by age of father and of age-specific mortality rates reported for the United States in 1964. These rates were then applied to the estimated number of persons examined in each age-sex group in order to estimate the future progeny expected for such persons. Each gonad dose was multiplied by the number of persons who had the stated examination and by the expected future children to an individual in that group, and these values were summed over all age-sex-examination groups. The expected number of future children for the total population was derived in manner analogous to the calculation for persons who were examined, and this number was divided into the summed product described above. While GSD is not a measure of the biological effects of radiation, it is a convenient means for comparing the genetic impact of various sources of radiation. More importantly, it provides a means of evaluating the effects of the factors involved in the level of exposure resulting from medical roentgenology. The data presented here are based on a national study of the x-ray experience of the United States population, conducted by the National Center for Radiological Health, Public Health Service.