Effective dose reduction using collimation function in digital panoramic radiography and possible clinical implications in dentistry

The primary aim was to evaluate the effective dose for a full size panoramic image and nine different panoramic protocols using collimation. The secondary aim was to estimate possible reduction of effective dose in clinical situations.

Effective dose, according to International Commission on Radiological Protection 2007 was determined for a full size panoramic image and nine different panoramic protocols applying collimation on an anthropomorphic Rando phantom, using metal-oxide semiconductor field-effect transistor dosemeters. The collimation protocols were chosen based on common diagnostic questions. 10 exposures were made for each protocol using a Planmeca ProMax® 2D (Helsinki, Finland). The mean effective doses were calculated according to clinical default exposure settings and compared for all protocols. A retrospective analysis of 252 referrals to a specialist clinic in dentomaxillofacial radiology assessed usability and dose reduction applying nine different collimation protocols, based on possible collimation of panoramic images. Dose reduction was calculated applying collimation feature in comparison to constant use of full size panoramic imaging. Referrals were categorized according to indication for radiographic examination.

Effective dose of a full size panoramic radiograph was 17.6 µSv at 8 mA and 66 kV. The dose reduction for the collimated images compared to a full size panoramic radiograph ranged from 4.5 to 86.9%. Potential total dose reduction in the studied sample was 35% if collimation feature had been applied. In four out of five of the referrals, collimation was possible and in 61% of the referrals the indication for radiographic examination was restricted to the dental alveolar region, reducing the dose by 40.3% compared with a full size panoramic image.

Since the effective dose may be reduced without losing diagnostic information in the area of interest, collimation feature of panoramic imaging should be routinely applied when the diagnostic task allows.