• Stuart L Cohen, Jason J Wang, Nicholas Chan, William O'Connell, Rakesh Shah, Pina Sanelli, and Suhail Raoof.
• Imaging Clinical Effectiveness and Outcomes Research (ICEOR), Department of Radiology, Northwell Health and the Center for Health Innovations and Outcomes Research (CHIOR), Feinstein Institutes for Medical Research and Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, Manhasset NY; Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, Lenox Hill Hospital/ Northwell Health, New York, NY. Electronic address: slcohen@northwell.edu.
• Chest. 2019 Dec 1; 156 (6): 1214-1222.

BackgroundEffective dose (ED) is used to understand radiation-related cancer risk of CT scans. Currently, ED for low-dose CT (LDCT) lung cancer screening (LCS) is estimated by multiplying the CT scan-reported dose-length product (DLP) by a DLP-to-ED conversion factor (k-factor) for general chest CT imaging, which does not account for sex. The purpose of this study was to calculate sex-specific k-factors for LDCT LCS.MethodsThis retrospective study evaluated consecutive LCS patients across a large health system from 2016 to 2017. Patient and CT scan-related data were obtained from the radiology information system, the picture archiving and communication system, and a radiation dose index-monitoring system. Each patient's ED was determined by patient-specific Monte-Carlo simulation using Cristy phantoms and divided by study DLP to determine the k-factor. The k-factors were compared vs the standard of 0.014 mSv·mGy⁻1·cm⁻1 for a chest CT scan by using a one-sample Student t test. Bivariate and multivariable analyses were performed for k-factors based on patient and CT scan factors.ResultsA total of 1,890 patients were included in the study. The mean k-factor for all patients was 0.0179 mSv·mGy⁻1·cm⁻1, which was 22% greater than the standard value of 0.014 mSv·mGy⁻1·cm⁻1 for a chest CT scan previously applied to LDCT imaging (P < .001). The mean k-factor in women (0.0213 mSv·mGy⁻1·cm⁻1) was 43% greater than in men (0.0149 mSv·mGy⁻1·cm⁻1) in the multivariable model (P < .001).ConclusionsThe overall k-factor for LCS is higher than the previously used value for chest CT imaging; when stratified according to sex, it was 43% greater in women than in men. Sex- and LCS-specific k-factors should be used to estimate effective radiation dose in LCS programs.Copyright © 2019 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.

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