Ruben Pauwels1,2, Reinhilde Jacobs3, Ria Bogaerts4, Hilde Bosmans5, Soontra Panmekiate6. 1. Department of Radiology, Faculty of Dentistry, Chulalongkorn University, 34 Henri-Dunant Rd, Patumwan, 10330, Bangkok, Thailand. ruben.pauwels@med.kuleuven.be. 2. OMFS-IMPATH Research Group, Department of Imaging and Pathology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium. ruben.pauwels@med.kuleuven.be. 3. OMFS-IMPATH Research Group, Department of Imaging and Pathology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium. 4. Laboratory of Experimental Radiotherapy, Department of Oncology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium. 5. Medical Physics & Quality Assessment, Department of Imaging and Pathology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium. 6. Department of Radiology, Faculty of Dentistry, Chulalongkorn University, 34 Henri-Dunant Rd, Patumwan, 10330, Bangkok, Thailand.
Abstract
OBJECTIVES: To estimate the possible reduction of tube output as a function of head size in dental cone-beam computed tomography (CBCT). METHODS: A 16 cm PMMA phantom, containing a central and six peripheral columns filled with PMMA, was used to represent an average adult male head. The phantom was scanned using CBCT, with 0-6 peripheral columns having been removed in order to simulate varying head sizes. For five kV settings (70-90 kV), the mAs required to reach a predetermined image noise level was determined, and corresponding radiation doses were derived. Results were expressed as a function of head size, age, and gender, based on growth reference charts. RESULTS: The use of 90 kV consistently resulted in the largest relative dose reduction. A potential mAs reduction ranging from 7 % to 50 % was seen for the different simulated head sizes, showing an exponential relation between head size and mAs. An optimized exposure protocol based on head circumference or age/gender is proposed. CONCLUSIONS: A considerable dose reduction, through reduction of the mAs rather than the kV, is possible for small-sized patients in CBCT, including children and females. Size-specific exposure protocols should be clinically implemented. KEY POINTS: • Fixed exposure settings in CBCT results in overexposure for smaller patients • For children, considerable dose reduction is possible without compromising image quality • A reduction in mAs is more dose-efficient than a kV reduction • An optimized exposure protocol was proposed based on phantom measurements • This protocol should be validated in a clinical setting.
OBJECTIVES: To estimate the possible reduction of tube output as a function of head size in dental cone-beam computed tomography (CBCT). METHODS: A 16 cm PMMA phantom, containing a central and six peripheral columns filled with PMMA, was used to represent an average adult male head. The phantom was scanned using CBCT, with 0-6 peripheral columns having been removed in order to simulate varying head sizes. For five kV settings (70-90 kV), the mAs required to reach a predetermined image noise level was determined, and corresponding radiation doses were derived. Results were expressed as a function of head size, age, and gender, based on growth reference charts. RESULTS: The use of 90 kV consistently resulted in the largest relative dose reduction. A potential mAs reduction ranging from 7 % to 50 % was seen for the different simulated head sizes, showing an exponential relation between head size and mAs. An optimized exposure protocol based on head circumference or age/gender is proposed. CONCLUSIONS: A considerable dose reduction, through reduction of the mAs rather than the kV, is possible for small-sized patients in CBCT, including children and females. Size-specific exposure protocols should be clinically implemented. KEY POINTS: • Fixed exposure settings in CBCT results in overexposure for smaller patients • For children, considerable dose reduction is possible without compromising image quality • A reduction in mAs is more dose-efficient than a kV reduction • An optimized exposure protocol was proposed based on phantom measurements • This protocol should be validated in a clinical setting.
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