INTRAORAL RADIOGRAPHS—A COMPARISON OF DOSE REDUCTION WITH COLLIMATION AND THYROID SHIELDING

Abstract

<h3>BACKGROUND</h3> The National Commission on Radiation Protection has reinforced its recommendation for the use of rectangular collimation for intraoral radiography in the most recent Report No. 177. In response to growing concern for the risks associated with dental diagnostic imaging, adoption of the concept of ALARA (as low as reasonably achievable) has inspired multiple modifications in collimator design approaches for reducing patient dose. <h3>OBJECTIVE(S)</h3> This intraoral study compared effective dose (E) using circular and rectangular collimator (RC) modalities. <h3>STUDY DESIGN</h3> Simulated 18-projection adult and 12-projection child full mouth series were exposed using a 6-cm-diameter circular collimator, a factory rectangular position-indicating device (PID) (Focus-RC), and 5 alternative universal RC modalities—JadRad-RC, Rinn-RC, Durr-RC, DexShield-RC, and TruAlign-RC—for both adult and child phantoms. Dosimetry was acquired using optically stimulated luminescence dosimeters placed at 24 anatomic sites in the head/neck region. Exposures were made with a Focus Instrumentarium Intraoral source using 70 kVp and total of 5.34 mA (adult) and 2.7 mA (child). <h3>RESULTS</h3> Adult E was lowest for Focus-RC (54 µSv), which also produced the greatest exposure area reduction (51%) compared with the circular collimator, followed by JadRad-RC (61 µSv), Rinn-RC (68 µSv), Durr-RC (69 µSv), DEXShield-RC (79 µSv), TruAlign-RC (79 µSv), and circular (90 µSv). Child E followed a similar trend: Focus-RC (44 µSv), JadRad-RC (49 µSv), Rinn-RC (53 µSv), Durr-RC (53 µSv), DEXShield-RC (60 µSv), TruAlign-RC (79µSv), and circular (92 µSv). Thyroid dose was reduced by as much as 59% using added shielding with circular techniques. RC with thyroid shielding reduced dose to the thyroid by as much as 87%. <h3>DISCUSSION/CONCLUSIONS</h3> Focus-RC techniques yielded the greatest dose reduction compared with alternative rectangular techniques and circular collimation. However, collimator dimensions, in addition to shape, should be considered as a significant factor in affecting patient effective dose. Rectangular collimation alone yielded a greater reduction in thyroid dose than did circular collimation with thyroid shielding.