Patient exposure to ionizing radiation in dental radiography.

Abstract

The use of ionizing radiations and exposure of the individual are increasing. As larger segments of the population are being exposed, two important requirements become apparent. The first is that exposures to various radiations be accurately evaluated; the second, that all possible means be taken to reduce exposures in necessary medical and dental procedures. In dental radiography, patient exposure may be reduced by the use of faster films, increased focal skin distance, and more penetrating radiation. The effects of these factors have been considered by various authors. Trout, Kelley and Cathey (1) and Seeman and Cleare (2) have shown that with increased filtration substantial reduction in the dosage to the skin and the first few millimeters of underlying tissue is possible without affecting the diagnostic value of the resulting roentgenograms. The use of such filtration results in a roentgen beam having greater penetration and thereby reduces the ratio of skin to bone dosage. This reduction in skin dose is due to the increase in the ratio of radiation incident upon the skin to that which is useful in producing the x-ray image. The quality of the beam may be further improved by raising the operating potential from the usual 60 or 65 kvp to the range between 85 and 100 kvp. Increase of the focal skin distance from 8 to 16 inches will further favorably increase the ratio of radiation incident on the skin to that which is useful in producing a radiographic image. For example, if the film is so placed that the beam has traversed 4 cm. before striking it, the increase in radiation reaching it will be 19 per cent. The employment of ultra-speed film in those cases which will allow its use can further reduce exposure of all tissues irradiated by a factor of four (3). The object of the investigation to be reported here was to determine the dose delivered to the apical areas during dental radiography, under certain operating conditions. The conditions chosen were the usual operating voltages, i.e., 60 and 65 kvp, added filtration of 0 and 1.0 mm. aluminum, and an 8-inch focal skin distance. The inherent filtration of the machine which was used is 1.2 mm. aluminum (including tube wall, oil, and cone). Method In order to simulate actual anatomical and geometrical conditions as closely as possible, a phantom head was constructed of Lucite, in sections projected from those given in Eycleshymer and Schoemaker (4). This was done so that all air cavities in the head and neck would be preserved in their relationship to each other and to solid tissue. This phantom, in a typical experimental set-up, is shown in Figure 1. To accommodate the ionization chamber, six holes were drilled in one side of the head and two holes in the neck. These holes were so cut and shaped that, when the ionization chamber was inserted, essentially no air cavity was present.