Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos Plus DS panoramic unit

Objectives: This study provides effective dose measurements for two extraoral direct digital imaging devices, the NewTom 9000(TM) cone beam CT (CBCT) unit and the Orthophos Plus DS panoramic unit. Methods: Thermo luminescent dosemeters were placed at 20 sites throughout the layers of the head and neck of a tissue-equivalent RANDO phantom. Variations in phantom orientation and beam collimation were used to create three different CBCT examination techniques: a combined maxillary and mandibular scan (Max/Man), a maxillary scan and a mandibular scan. Ten exposures for each technique were used to ensure a reliable measure of radiation from the dosemeters. Average tissue-absorbed dose, weighted equivalent dose and effective dose were calculated for each major anatomical site. Effective doses of individual organs were summed with salivary gland exposures (E-SAL) and without salivary gland exposures (E-ICRP60) to calculate two measures of whole-body effective dose. Results: The effective doses for CBCT were: Max/Man scan, E-ICRP60 = 36.3 muSv, E-SAL = 77.9 muSv; maxillary scan, E-ICRP60 = 19.9 muSv, E-SAL = 41.5 muSv; and mandibular scan, E-ICRP60 = 34.7 muSv, E-SAL = 74.7 muSv. Effective doses for the panoramic examination were E-ICRP60 = 6.2 muSv and E-SAL = 22.0 muSv. Conclusion: When viewed in the context of potential diagnostic yield, the E-ICRP60 of 36.3 muSv for the NewTom compares favourably with published effective doses for conventional CT (314 muSv) and film tomography (2 - 9 muSv per image). CBCT examinations resulted in doses that were 3 - 7 (E-ICRP60) and 2-4 (E-SAL) times the panoramic doses observed in this study.