Reducing transmitted radiation in dental radiography.

A significant amount of radiation escapes the rear of an image receptor in conventional dental radiographic procedures despite the placement of a lead-containing backing at the rear of the film pack. The purpose of this investigation was to place additional layers of lead on the film pack in an attempt to reduce transmitted radiation to tissues behind the film. Reduction of dose to tissues behind the film causes a reduction in scatter radiation to critical organs such as the thyroid gland and salivary glands. A thermoluminescent lithium fluoride dosimetry system (TLD) was used and calibrated in both the beam of interest and tissue of interest. A tissue-equivalent anthropomorphic phantom was used for dose determination. Successive layers of lead foils were added to the image receptor, and dose was determined for each additional lead foil in the tissues behind the image receptor. Two sets of exposure conditions were used, namely: 70 kVp, 10 mA, and 0.6 s, and 90 kVp, 10 mA, and 0.6 s. The beam-film-patient orientation used was for a first molar bitewing radiographic projection. Four lead layers (three additional foils equalling 3.92 x 10(-3) mm of lead) on the conventional film package resulted in a significant dose reduction. Four layers of lead resulted in a dose less than one-third that of the conventionally shielded package.