(Thursday, 8/2/2018) 10:00 AM - 12:00 PM
Room: Room 202
Purpose: To purpose of the study is to derive gender-specific dose length product (DLP)–to-effective dose (ED) conversion factors for adult computed tomography (CT) examinations based on patient dosimetry data.
Methods: A radiation dose index monitoring (RDIM) system collected DLP; Volumetric Computed Tomography Dose Index (CTDIvol); Size Specific Dose Estimates (SSDE); Patient Water Equivalent Diameter (WED) and Scan Region for 1,423,708 adult CT examinations performed on fifty-two (52) CT scanners from 2014 through 2017. The RDIM generated Monte Carlo estimates of organ dose with subsequent approximation of ED via International Commission on Radiation Protection (ICRP) Report No. 103 tissue-weighting factors and methodology. Calculations segregate conversion factors according to target region (head; chest; abdomen and pelvis). The project also calculates ED via k-factor methodology described in American Association of Medical Physicist (AAPM) Report No 96.
Results: Calculated DLP-to-ED conversion factors for male adult abdomen, chest, head and pelvis examinations are 0.015 mSv/mGy-cm, 0.017 mSv/mGy-cm, 0.0024 mSv/mGy-cm and 0.013 mSv/mGy-cm, respectively. Conversion factors For female adult abdomen, chest, head and pelvis examinations are 0.017 mSv/mGy-cm, 0.023 mSv/mGy-cm, 0.0027 mSv/mGy-cm and 0.013 mSv/mGy-cm respectively.
Conclusion: For male examinations, DLP-to-ED conversion factors align well with existing k-factors. The calculated male abdomen conversion factor (0.015 mSv/mGy-cm) is identical to the abdomen k-factor cited in literature. Likewise, DLP-to-ED conversion factors for male examinations of the chest, head and pelvis agree with published values – 0.017 v. 0.014, 0.024 v. 0.021, and 0.013 v. 0.015 respectively. For female examinations, the calculated chest conversion factor of 0.023 mSv /mGy-cm is more than 50% higher than the gender-agnostic value of 0.014 mSv /mGy-cm. Lesser degrees of variation exist for abdomen (0.017 v. 0.015), head (0.0027 v. 0.0021) and pelvis (0.013 v. 0.015). Gender-agnostic DLP-to-ED conversion factors underestimate dose in female CT examinations of the chest.
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