Further Problems in X-Ray Protection

Abstract

The danger of excessive exposure to radiation in the operation of diagnostic roentgen equipment has been pointed out by a number of observers (Braestrup, 1; Bell, 2; Quimby, 3; Taylor, 4; the International X-ray and Radium Protection Commission, 5; the National Bureau of Standards, 6; White, Cowie and de Lorimier, 7). Most of these reports have been concerned with the radiation hazards associated with roentgenoscopy. It is the purpose of this communication, the first of a series of three, to describe the exposure conditions which are more or less typical of photofluorography. Recommendations for the adequate protection of personnel operating photofluorographic units will be included in the third paper of the series. The radiation hazards associated with the operation of photofluorographic equipment are particularly severe. The volume of work is often large, sometimes reaching 400 to 800 exposures daily. Furthermore, the quantity of radiation per exposure is considerably greater than that in standard chest roentgenography. Finally, the equipment is often portable and installation is of temporary character, circumstances which are conducive to faulty protective measures. Equipment The investigations reported in this paper were conducted with one of the photofluorographic units being used by the Tuberculosis Control Division of the U. S. Public Health Service. The unit included a 200-ma. x-ray machine equipped with a rotating anode tube, with a housing constructed of steel and lined with lead; a lead cone extending from the anode housing limited the primary x-ray beam. Portable V-shaped floor screens containing 1/16-inch sheet lead shielded the operator and positioners. The arrangement of the photofluorograph and protective screens is shown schematically in Figure 1. Measurements of the quantity of radiation received at various locations about the photofluorographic enclosure were made with a Victoreen ionization instrument employing both 0.25-r and 25-r ionization chambers. Calibration and leakage were checked prior to and during usage, and in most cases a sufficient number of exposures to give at least a half-scale reading were made. It is recognized that there is some question as to the reliability of the readings made with these ionization chambers when radiation of relatively long wave length, such as is customarily employed in diagnostic radiology, is being measured. White et al. (7) have investigated this point and have found no serious error in the Victoreen chamber (i.e., no error greater than 10 per cent) in the normal range of x-ray-tube voltages employed in diagnostic radiography. Measurements with 35-mm. and 14 × 17-inch Technics To compare the quantity of radiation required for 35-mm. chest photofluorography with that required for ordinary 14 × 17-in. celluloid films, measurements were made by suspending ionization chambers over the chest anteriorly and posteriorly, with the patient standing in the usual position.