(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: get slice and volume average absorbed dose indexes inside and outside field of view (FOV) when an uniform cylindrical polymethyl methacrylate (PMMA) phantom (UCphantom) is scanned by dental and maxillofacial cone beam computed tomography (dental CBCT) with standard-scan mode (full-fan X-ray collimation, full-scan (360 degree angle range) mode and UCphantom centering at dental CBCT`s isocenter).
Methods: doses inside UCphantom are measured by thermoluminicence detectors (TLD). These distributions are fitted to empirical quadratic equation models. As a result, slice and volume average absorbed dose inside and outside FOV are predicted by limited measured absorbed doses. These are validated by relative deviations to detailed experimental datasets.
Results: at phantom diameter orientation conform to piecewise quadratic equation with division being FOV diameter. Those at Z direction inside FOV height limits conform to direct quadratic equation. As an inference, inside FOV volume, slice average absorbed dose is the summation of 1/2 UCphantom central and 1/2 FOV edge absorbed dose; volume average absorbed dose is the summation of 2/3 central and 1/3 FOV top (or bottom) slice average absorbed dose. Outside FOV volume, the same ways applied but with the replacement of FOV edge and UCphantom edge absorbed dose during slice average absorbed dose calculation. In UCphantom volume bounded by FOV height, slice and volume average absorbed dose are the mass weighted summation of those being inside and outside FOV volume. They consist standard-scan mode cone beam computed tomography dose index (CBCT) series with less than 5% relative deviations for two representatives of dental CBCT equipments.
Conclusion: CBCT dose estimations at standard-scan mode bounded by FOV range can be effectively inferred by cone beam dose indexe (CBDI) series. They are slice average absorbed dose indexes as ?CBDI?_s^In, ?CBDI?_s^Out and ?CBDI?_s^PHAN, and volume average absorbed dose indexes as ?CBDI?_v^In, ?CBDI?_v^Out and ?CBDI?_v^PHAN.
Funding Support, Disclosures, and Conflict of Interest: National Natural Science Foundation of China
Keywords
Cone-beam CT, Dose, Dosimetry Protocols
Taxonomy
IM- Cone Beam CT: Radiation dosimetry & risk
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