Effective doses of NewTom VGi variable volume dental CBCT unit

Objectives: Use of variable fields of view (FOV) to limit CBCT image volumes to specific regions of interest (ROI) is a potential means of reducing risk from CBCT imaging. The effectiveness of this approach was evaluated using the NewTom VGi unit by measuring effective dose for a variety of FOVs and ROIs.

Methods: Dosimetry of 6x6cm to 15x15cm FOVs at various resolutions were evaluated using Optical Stimulated Luminescent dosimeters (Landauer NanoDot) placed at 24 locations within and on a RANDO phantom (Ludlow et al 2008). Effective dose was derived using the 2007 ICRP calculation. Exposure settings were optimized for image quality and patient size by the automatic exposure control function of the unit. Data were evaluated with ANOVA.

Results: Significant increases in dose were related to increasing FOV (p=0.015). Significant increases in dose were also related to increasing resolution (p=0.048).

Table: Effective Dose by FOV size and resolution

FOV size and resolution	15x15cm standard resolution	12x15cm standard resolution	8x12cm standard resolution	8x8cm standard resolution	8x12cm high resolution	8x8cm high resolution
Effective Dose in µSv	99	86	69	51	235	172

Table: Effective Dose by location and jaw for 6x6cm high resolution FOV

location	posterior	anterior	posterior	anterior
Jaw	mandible	mandible	maxilla	maxilla
Effective Dose in µSv	160	117	109	109

Conclusions: Use of variable FOVs and standard resolution reduced dose in every instance in comparison with larger FOVs of the same region or higher resolution.

This research was supported by ImageWorks, Elmsford, NY and NIDCR grant 1R21DE022160-01