Radiation Dose Comparison of CBCT and CT Extremity Scans


Amanda Smith BSc1, Maria Cavadas BSc1, Shahed Khan MPhil2, Veronique Sauret-Jackson MSc PhD1 1Cavendish Imaging Ltd, 2Radiation Consultancy Services Ltd.

“Could CBCT provide a sufficient alternate to Conventional CT?”

In current clinical practice Cone Beam CT [CBCT] is prolifically used for dental and maxillofacial conditions, however research shows that CBCT could be advantageous over CT for scanning extremities.

Conventional CT uses a fan beam and the X-ray tube rotates around the patient several times in order to obtain the scan acquisition1. CBCT however, uses a cone-shaped beam and different kV and mAs settings in order to obtain the scan from a single rotation. This delivers a lower radiation dose.

Patient positioning for a CBCT wrist examination with the NewTom 5G


The Dose Length Product [DLP] readings and the corresponding scan length were recorded retrospectively for extremities imaged with the NewTom 5G and the GE VCT. The DLP/Scan Length ratio was used to standardise the DLP readings and give a ‘dose score’ for comparison.

Dose Score Comparison (mGy)



Fig 3 and 4 show an example of the visual appearance for a knee axial slice and corresponding DLP readings. The analysis of dose for each area of interest revealed that the CBCT scores were 65-92% lower than the scores from conventional CT.

Fig 3 CBCT Axial Knee

Fig 4 CT Axial Knee


When comparing doses between CBCT and conventional CT scanners using the DLP/Scan Length as the score, findings suggest that the radiation dose to the patient undergoing an extremity CT scan is significantly higher than that delivered to the patient undergoing CBCT.

Dose Score Comparison (mGy)