Masoumeh Parsi1, Mehdi Sohrabi2, Fereidoun Mianji3, Reza Paydar4. 1. Health Physics and Dosimetry Research Laboratory, Department of Energy Engineering and Physics, Amirkabir University of Technology, Tehran, Iran. 2. Health Physics and Dosimetry Research Laboratory, Department of Energy Engineering and Physics, Amirkabir University of Technology, Tehran, Iran. Electronic address: dr_msohrabi@yahoo.com. 3. Nuclear Science and Technology Research Institute, Tehran, Iran. 4. Radiation Sciences Department, Faculty of Allied Medicine, Iran University of Medical Sciences, Tehran, Iran.
Abstract
PURPOSE: A new quality-control-based (QC-based) method is introduced to obtain correction factors to be applied to displayed patient dose indices (CTDIVol and DLP) on CT scanner consoles to verify improvement of dose surveys for diagnostic reference levels (DRLs) determination. METHOD: An available data-base of QC documents and reports of 57 CT scanners in Tehran, Iran was used to estimate CTDIVol, DLP and relevant correction factors for three CT examination types including head, chest and abdomen/pelvis. The correction factor is the ratio of QC-based estimated dose to displayed dose. A dose survey was performed by applying on-site "data collection method" and correction factors obtained in order to select CT scanners in three modes for determination of CT DRLs by inclusion of: (a) all CT scanners before displayed dose indices were corrected (57), (b) only CT scanners calibrated by QC experts (41) and (c) all CT scanners after displayed dose indices were corrected (57). RESULTS: For the 41 CT scanners, correction factors of three examination types obtained in this study are within the acceptance tolerance of IAEA HHS-19. The correction factors range from 0.45 to 1.7 (average of 3 examinations) which is due to the change in the calibrated value of CTDIVol over extended time. The DRL differences in three modes are within ±1.0% for CTDIVol and ±12.4% for DLP. CONCLUSIONS: The "QC-based correction method" applied to mode (c) has improved the DRLs obtained by other two modes. This method is a strong alternative to "direct dose measurement" with simplicity and cost effectiveness.
PURPOSE: A new quality-control-based (QC-based) method is introduced to obtain correction factors to be applied to displayed patient dose indices (CTDIVol and DLP) on CT scanner consoles to verify improvement of dose surveys for diagnostic reference levels (DRLs) determination. METHOD: An available data-base of QC documents and reports of 57 CT scanners in Tehran, Iran was used to estimate CTDIVol, DLP and relevant correction factors for three CT examination types including head, chest and abdomen/pelvis. The correction factor is the ratio of QC-based estimated dose to displayed dose. A dose survey was performed by applying on-site "data collection method" and correction factors obtained in order to select CT scanners in three modes for determination of CT DRLs by inclusion of: (a) all CT scanners before displayed dose indices were corrected (57), (b) only CT scanners calibrated by QC experts (41) and (c) all CT scanners after displayed dose indices were corrected (57). RESULTS: For the 41 CT scanners, correction factors of three examination types obtained in this study are within the acceptance tolerance of IAEA HHS-19. The correction factors range from 0.45 to 1.7 (average of 3 examinations) which is due to the change in the calibrated value of CTDIVol over extended time. The DRL differences in three modes are within ±1.0% for CTDIVol and ±12.4% for DLP. CONCLUSIONS: The "QC-based correction method" applied to mode (c) has improved the DRLs obtained by other two modes. This method is a strong alternative to "direct dose measurement" with simplicity and cost effectiveness.