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Do we need 3D tube current modulation information for accurate organ dosimetry in chest CT? Protocols dose
Xochitl Lopez-Rendon1, Guozhi Zhang2, Walter Coudyzer2
1Department of Imaging and Pathology, Division of Medical Physics & Quality Assessment, KU Leuven, Herestraat 49, Leuven, 3000, Belgium. xochitl.lopezrendon@uzleuven.be.
Objectives:
To compare the lung and breast dose associated with three chest protocols: standard, organ-based tube current modulation (OBTCM) and fast-speed scanning; and to estimate the error associated with organ dose when modelling the longitudinal (z-) TCM versus the 3D-TCM in Monte Carlo simulations (MC) for these three protocols.
Method:
Five adult and three paediatric cadavers with different BMI were scanned. The CTDIvol of the OBTCM and the fast-speed protocols were matched to the patient-specific CTDIvol of the standard protocol. Lung and breast doses were estimated using MC with both z- and 3D-TCM simulated and compared between protocols.
Results:
The fast-speed scanning protocol delivered the highest doses. A slight reduction for breast dose (up to 5.1%) was observed for two of the three female cadavers with the OBTCM in comparison to the standard. For both adult and paediatric, the implementation of the z-TCM data only for organ dose estimation resulted in 10.0% accuracy for the standard and fast-speed protocols, while relative dose differences were up to 15.3% for the OBTCM protocol.
Conclusion:
At identical CTDIvol values, the standard protocol delivered the lowest overall doses. Only for the OBTCM protocol is the 3D-TCM needed if an accurate (<10.0%) organ dosimetry is desired.
Key Points:
• The z-TCM information is sufficient for accurate dosimetry for standard protocols. • The z-TCM information is sufficient for accurate dosimetry for fast-speed scanning protocols. • For organ-based TCM schemes, the 3D-TCM information is necessary for accurate dosimetry. • At identical CTDI vol , the fast-speed scanning protocol delivered the highest doses. • Lung dose was higher in XCare than standard protocol at identical CTDI vol .
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