Estimation of effective doses from MDCT and CBCT imaging of extremities

Little research has been published on the radiation burden of cone beam computed tomography (CBCT) in comparison with multi-row detector computed tomography (MDCT) for extremity imaging. This manuscript reports effective doses produced by standard and reduced dose imaging protocols for a 128-slice MDCT unit and a dedicated extremity imaging device using CBCT technology. Anthropomorphic phantoms with x-ray attenuation characteristics simulating adult hand-wrist, foot-ankle, and knee areas were modified to receive optically stimulated luminescent dosimeters (OSL). Standard and lower kVp reduced dose (Lite) exposures were compared. Effective doses for four age groups (five years old to adult) were calculated following 2007 recommendations of the ICRP. Standard CBCT imaging protocols produced effective doses (1.3-21.1 μSv) that were on the order of daily US ubiquitous background radiation doses. CBCT doses were on average 90% less than comparable MDCT views of the same anatomy (9.1-204 μSv). Child doses were significantly greater than adult doses (p = 0.0001). CBCT doses could be further reduced by 36%-51% with Lite exposure protocols. These protocols can be recommended for children and in cases where increased image noise will not interfere with the diagnostic task.