A Limited Survey of Radiation Exposure from Dental X-ray Units

Abstract

The Department of Public Health of the City of Philadelphia, as a part of its expanding program in radiation hazard control, instituted in 1956 a study of radiation exposure from various medical x-ray units. Of the x-ray machines commonly used for medical diagnosis, dental units were chosen for initial investigation because of their number and wide use and because the training of personnel in the measurement of their radiation characteristics is relatively easy. The purpose of the limited survey described below was to estimate how much radiation dentists, their assistants, and their patients are receiving and to provide a basis for consideration of practical methods for reducing unnecessary radiation exposure. Methods Measurements made on 56 dental x-ray units are included in the present study. Thirteen dental units were in city clinics and institutions, one was in a private hospital, and the remaining 42 were in the offices of dentists engaged in private practice. All calibrations and radiation surveys were performed under the operating conditions normally employed by the dentist in charge. In most instances, information concerning the tube potential and the total filtration was either lacking or was considered unreliable. The following measurements were made: 1. The exposure dose rate in roentgens per minute was measured in air with Victoreen 25-r ionization chambers placed at the tip of the cone normally used. 2. The “quality” of the radiation was determined by measuring the half-value layer (h.v.l.) in aluminum. Calibrated aluminum filters, 6 inches square, were used for transmission measurements. The distance between the filters and the ionization chamber was about 11 cm. 3. The size of the primary x-ray beam at the tip of the cone was determined by exposing x-ray film at that position. 4. The scattered and leakage radiation field in the vicinity of the x-ray tube head, with the primary beam directed toward the floor, was investigated with an ionization rate meter. For these measurements, a cube of maple wood, 13 cm. on each side, was positioned at the tip of the cone to serve as a “phantom” head. The approximate exposure dose rate at 1 meter from the cone tip and in a direction perpendicular to the primary beam axis was interpolated from the plotted data. 5. In order to estimate the exposure received by the dentists and their assistants, each was supplied with radiation monitoring film badges obtained from a commercial film badge service. The badges were worn about the chest for either one or two weeks. Each person monitored was asked to keep a record of the total milliampere-seconds of x-ray exposure made while in the vicinity of the x-ray machine. In some cases, the study was repeated. 6. In order to obtain an index of the radiation exposure to the patient, each dentist was asked for the exposure time he normally used for making periapical molar roentgenograms of adult patients.