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Dose Measurement Methodology for Dental Cone-Beam CT

N Ford

P Deman1, P Atwal2, C Duzenli2, Y Thakur3, N Ford1*, (1) University of British Columbia, Vancouver, BC,(2) British Columbia Cancer Agency, Vancouver, BC, (3) Vancouver General Hospital, Vancouver, BC

SU-E-I-10 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Dental Cone Beam CT (CBCT) was introduced to perform 3D high resolution imaging at lower dose than multi-slice CT (MSCT). No consensus has been found to measure the dose delivered by this equipment, unlike the CTDI measurement used for the narrow beam MSCT. The goal of this study is to determine the suitability of the dosimetry methods published in AAPM Report 111 for dental equipment.

Methods: A protocol derived from one proposed by Dixon et al. was applied to dose measurements of MSCT, dental CBCT (small and large fields of view) and a dental panoramic system. The CTDI protocol was also performed on the MSCT to compare both methods under different scanning conditions. Experiments were executed to characterize the dose distribution using a thimble ionization chamber (dose free-in-air, dose in a CTDI phantom) and gafchromic film (beam profiles, dose in an anthropomorphic phantom). Experiments were performed on the CBCT with a CTDI head phantom alone and with the head phantom placed on a body phantom to measure the importance of scattered radiation due to the chest.

Results: The dose measured in the centre of the phantom and field of view from the large field of view dental CBCT (11.4 mGy/100mAs) is 2 times lower than that of MSCT (20.7 mGy/100mAs) for the same FOV, but approximately 20 times higher than for a panoramic system (0.6 mGy/100mA.s). The impact of scattered radiation due to the chest phantom measured with the Dixon et al. method was not significant. The dose distributions measured with the PMMA phantom and the anthropomorphic phantom were similar.

Conclusion: Although the dose delivered by the dental CBCT was reduced by a factor of 2 compared to MSCT for the same field of view, it is approximately 20 times higher than the dose delivered by the panoramic system.

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