The National Commission on Radiation Protection and Measurements has reinforced its
recommendation for the use of rectangular collimation for intraoral radiography in
its Report No. 177 published in 2019. This study compared effective dose (E) using
circular and rectangular collimator (RC) modalities.
The authors exposed 18 projections for adult and 12 projections for child full-mouth
series using an original equipment 6 centimeter diameter circular collimator (circular),
original equipment rectangular positioning indicator device (Focus-RC), and 5 universal
RC modalities (JadRad-RC, Rinn-RC, Durr-RC, DEXshield-RC, and TruAlign-RC) for adult
and child phantoms. The authors acquired dosimetry using optically stimulated luminescence
dosimeters. Exposures were made with a Focus (Instrumentarium) intraoral source using
70 peak kilovoltage and total milliamperes of 5.34 (adult) and 2.7 (child).
Adult E was lowest for Focus-RC (54 microsieverts), which also produced the greatest
exposure area reduction (51%) compared with circular, followed by JadRad-RC (55 μSv),
Durr-RC (58 μSv), Rinn-RC (62 μSv), DEXshield-RC (70 μSv), TruAlign-RC (85 μSv), and
circular (86 μSv). Child E followed a similar trend: Focus-RC (44 μSv), JadRad-RC
(44 μSv), Durr-RC (45 μSv), Rinn-RC (48 μSv), DEXshield-RC (53 μSv), TruAlign-RC (85
μSv), and circular (89 μSv). When used with thyroid shielding, circular collimation
thyroid dose was reduced by as much as 59%.
Focus-RC techniques yielded the greatest dose reduction compared with alternative
RC and circular. In addition to shape, collimator dimensions should be considered
as significant factors affecting patient E. RC alone yielded a greater reduction in
thyroid dose than did circular with thyroid shielding.
This study’s findings underscore the updated recommendations of the National Commission
on Radiation Protection and Measurements Report No.177, which emphasized the benefits
and important practical considerations of RC with intraoral imaging.