Dosimetry of 3 CBCT devices for oral and maxillofacial radiology: CB Mercuray, NewTom 3G and i-CAT

TLDR

Cone‑beam CT offers a lower‑dose, lower‑cost alternative to conventional CT and is increasingly used in oral and maxillofacial radiology. This study compares the effective radiation dose of three large‑field‑of‑view CBCT units—CB Mercuray, NewTom 3G, and i‑CAT. Effective dose was measured in a tissue‑equivalent skull phantom using thermoluminescent dosimeters at 24 sites, with doses summed by ICRP weighting factors for 1990 and 2005 draft tissue weights, and expressed as multiples of panoramic radiography. The measured effective doses were 45–59 µSv for NewTom 3G, 135–193 µSv for i‑CAT, and 477–558 µSv for CB Mercuray—4 to 42 times higher than panoramic imaging, with dose reductions achievable by decreasing field size and mA/kV, and CBCT doses remaining several times higher than panoramic but an order of magnitude lower than conventional CT.

Abstract

Cone beam computed tomography (CBCT), which provides a lower dose, lower cost alternative to conventional CT, is being used with increasing frequency in the practice of oral and maxillofacial radiology. This study provides comparative measurements of effective dose for three commercially available, large (12'') field-of-view (FOV), CBCT units: CB Mercuray, NewTom 3G and i-CAT.Thermoluminescent dosemeters (TLDs) were placed at 24 sites throughout the layers of the head and neck of a tissue-equivalent human skull RANDO phantom. Depending on availability, the 12'' FOV and smaller FOV scanning modes were used with similar phantom positioning geometry for each CBCT unit. Radiation weighted doses to individual organs were summed using 1990 (E(1990)) and proposed 2005 (E(2005 draft)) ICRP tissue weighting factors to calculate two measures of whole-body effective dose. Dose as a multiple of a representative panoramic radiography dose was also calculated.For repeated runs dosimetry was generally reproducible within 2.5%. Calculated doses in microSv [corrected] (E(1990), E(2005 draft)) were NewTom3G (45, 59), i-CAT (135, 193) and CB Mercuray (477, 558). These are 4 to 42 times greater than comparable panoramic examination doses (6.3 microSv [corrected] 13.3 mSv). Reductions in dose were seen with reduction in field size and mA and kV technique factors.CBCT dose varies substantially depending on the device, FOV and selected technique factors. Effective dose detriment is several to many times higher than conventional panoramic imaging and an order of magnitude or more less than reported doses for conventional CT.