The overall dose length product-(DLP) to-effective dose conversion factor (k-factor) for lung cancer screening is higher than the value previously used for chest computed tomography (CT), according to a study published in CHEST.

Furthermore, when stratified by gender, the k-factor was 43% greater in women compared with men, indicating the need for lung cancer screening and gender-specific k-factors when estimating effective radiation dose.

Currently the effective dose used to understand the radiation-related cancer risk of low-dose computed tomography (LDCT) lung cancer screening is estimated by a general chest CT that does not account for gender. This retrospective study was designed to determine accurate gender-specific k-factors for LDCT lung cancer screening by evaluating consecutive patients aged 55 to 80 years across a multihospital integrated healthcare network from 2016 through 2017. CT-related and patient data were obtained from the radiation dose index monitoring system, the radiology information system, and the picture archiving and communication system.

Individual patient effective doses were determined using Cristy phantoms for patient-specific Monte-Carlo simulations, and k-factors were determined by dividing each patient’s effective dose by study DLP. The average overall k-factor for men and women was compared with the standard of 0.014 mSv·mGy⁻¹·cm⁻¹ for chest CT with one-sample t-test. Multivariable linear regression and bivariate analyses for k-factor were performed based on CT and patient factors.

A total of 1890 studies were included, with 1013 men (53.6%) and 877 women (46.4%). The mean k-factor for all participants was 0.0179 mSv·mGy⁻¹·cm⁻¹, which is 22% greater than the standard value of 0.014 mSv·mGy⁻¹·cm⁻¹ (P <.001) for chest CT previously applied to LDCT. The mean k-factor in women was 34% greater than the standard (0.0213) compared with 6% greater than the standard (0.0149) in men (P <.001). On multivariable analysis after adjustments for technical and patient factors, k-factors for women were 43% higher than for men, indicating that instead of an estimated dose of 1.35 mSv regardless of gender, the dose should be 1.44 mSv for men and 2.06 mSv for women.

Despite limitations such as the data being extracted from a single healthcare system and dependence on Cristy phantoms, the investigators concluded that “this study does reflect real-world experience with a large sample size over a span of multiple years that has practical implications for guiding patient management.”

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“As we learn more about lung cancer screening, certain populations may benefit from decreased screening frequency and reduced age inclusion criteria,” the researchers wrote. “As such there may be more personalized recommendations related to lung cancer screening criteria based on predicted mortality benefits. These criteria may take into account many factors including gender, race, predicted surgical success (symptoms, pulmonary function tests, emphysema, etc) and comorbidities that may affect patients’ life expectancies.”

Reference

Cohen SL, Wang JJ, Chan N, et al. Lung cancer screening CT: Gender-specific conversion factors to estimate effective radiation dose from dose length product [published online August 14, 2019]. CHEST. doi:10.1016/j.chest.2019.07.024