A limited survey of radiation exposure from medical fluoroscopes.

Abstract

With the co-operation of the University of Pennsylvania and dentists and physicians of Philadelphia, the Department of Public Health of the City of Philadelphia instituted in 1956 a study of radiation exposure from medical x-ray units. A survey of dental x-ray units has previously been reported (1). The present paper is concerned with the radiation characteristics of fluoroscopes surveyed in the Philadelphia area and some of the problems involved in controlling unnecessary radiation exposure from their use. Method of Survey Measurements made on 81 fluoroscopes are included in the present study. Twenty-two units were owned by 8 hospitals4 and 4 city clinics, and the remaining 59 were in the offices of physicians engaged in private practice. The distribution of the units according to ownership is presented in Table I. They are listed according to type and manufacturer in Table II. Sixty-seven fluoroscopes were located within the city limits of Philadelphia. The other 14 were in eastern Pennsylvania and southern New Jersey. Twenty of the fluoroscopes, owned by hospitals and radiologists, were inspected at the request of the owners. The others, all in Philadelphia, were chosen at random from a list registered by physicians with the Commonwealth of Pennsylvania Department of Health. A survey and questionnaire form was used to record systematically four categories of information for each fluoroscope: (a) data from the physician concerning age, manner of use, and average work load; (b) physical inspection; (c) radiation characteristics; (d) radiation exposure to the physician. Measurement Technic The technics used to measure the radiation characteristics of the fluoroscopes were adapted with modifications for field use from methods developed and described by Hale et al. (2). Measurements were made with the field size of the primary x-ray beam ad just ed to 10 × 10 cm. at the panel surface or table top. Tube potential and current settings were those normally used by the physician. Exposure Dose Rate and Half-Value-Layer Measurements: The “quality” of the radiation was determined by measuring the half-value layer (h.v.l.) in aluminum by an inferential method (2, 3). The design of aluminum caps,5 varying in thickness, which were machined to fit over the sensitive volume of the Victoreen 25-r condenser ionization chamber,6 is shown in Figure 1. The ratio of the chamber reading with cap on to the reading with cap off was calibrated as a function of the h.v.l. (Fig. 2). The calibration curves were obtained by the method previously described (2). It can be seen in Figure 2 that the h.v.l. calibration curve for aluminum caps is independent of tube potential. Most of the h.v.l. determinations were made with caps 2 mm. and 3 mm. thick; the 3-mm. thickness was found to be most satisfactory. A second 25-r chamber was always used as a monitor to avoid uncertainty in measurements due to electrical instability.