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The reduction in radiation dose for intra-oral radiographs by the use of thin K-edge filters

Department of Dental Radiology, King's College School of Medicine and Dentistry, Denmark Hill, London SE5 9RS ^* Department of Medical Physics and Medical Engineering, King's College Hospital, Denmark Hill, London SE5 9RS, UK

The aim of this investigation was to reduce the radiation dose to patients undergoing intra-oral dental radiography by using thin K-edge filters in addition to the existing aluminium filter. The subject was a head phantom (a human skull embedded in tissue-equivalent material), which was exposed to X rays over a range of tube voltages (50–90 kVp) for each of the four filter systems. These were 2.7 mm aluminium alone (the existing total filtration) or with added 0.1 mm erbium, 0.1 mm yttrium or 0.05 mm niobium. The radiation dose was measured at four selected sites along the primary beam. These were the entrance skin dose, the exit skin dose and intra-orally both in front and behind the dental film packet. The exposure times and radiation doses required to produce an equivalent density (degree of blackening) on a radiograph of an upper molar tooth were determined. Within the usual diagnostic range of 60–80 kV the use of the thin K-edge filter resulted in a doubling of the exposure time (owing to the additional attenuation of the added filters). However, the skin dose and the total dose imparted to the patient were significantly reduced.

Key Words: Dental radiography • Filtration • Radiation dosage

Received for publication July 1, 1990. Revision received November 1, 1990.