Child and Adult Effective Dose Reduction From Intraoral Rectangular Collimators

Objectives: While the National Commission on Radiation Protection (NCRP) strongly recommends rectangular collimation for intraoral radiographic imaging, different devices have been shown to provide significantly different levels of dose reduction. The application of ALARA (As Low As Reasonably Achievable) requires that the effectiveness of different exposure reduction options be understood. Reduction in effective dose (E) by substituting rectangular collimation for round was measured using 4 rectangular collimator modalities.
Methods: Simulated 18 projection adult and 12 projection child full mouth series (FMX) were exposed using a 6 cm diameter Focus™ circular collimator (Circular), a Focus™ factory unit specific rectangular PID (Factory-RC), a Rinn® universal rectangular collimator (Universal-RC), a Tru-Align™ universal rectangular device (Enhanced-RC), and a Jad/Rad™ rectangular beam restricting alignment ring (Ring-RC) for both adult and child anthropomorphic phantoms. Dosimetry was acquired using optically stimulated luminescence (OSL) dosimeters placed at 24 anatomical sites in the head/neck region. All exposures were made with a Focus™ Intraoral X-ray unit using 70 kVp and total mAs of 37.4 (adult) and 18.9 (child). Tabulated results are reported below.
Results: Tabulated results are reported below.
Conclusions: Reduction in beam area reduced dose in both child and adult phantoms but was particularly effective for the child. Only the Factory-RC met NCRP standards for maximum collimator dimensions for both long and short dimensions. Rectangular collimation has been proven to reduce dose when compared to circular. However, rectangular dimensions and total area are critical to effective dose reduction. Compliance with NCRP guidelines for maximum field dimensions led to 48% effective dose reduction in the child and 38% in the adult.