The 2007 modification by the International Commission on Radiation Protection of the calculation of effective dose from ionizing radiation has renewed interest in the concept of As Low As Reasonably Achievable exposure, and the technical approaches for reducing doses. This intraoral imaging study compared effective doses from circular and rectangular collimator modalities. A total of 18-image adult and 12-image child full mouth series were exposed using a 6 cm diameter circular collimator, a universal rectangular collimator, and an enhanced rectangular device for both adult and child phantoms. Rectangular collimation significantly reduced doses for adult exposures. In the child sample, only the universal rectangular collimator achieved significant dose reduction. While dose differences were attributed to both the size of the rectangular field and the use of thyroid shielding, the results indicated that the universal rectangular collimator used alone was more effective at reducing thyroid exposure than a thyroid shield used with circular collimation.
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