E3261. CT Colonography Radiation Dose Trends in the United States
  1. Ezra Margono; Boston Medical Center
  2. Kevin Chang; Boston Medical Center
Colorectal cancer is the second leading cause of cancer death in the United States, and although the overall incidence and mortality are decreasing, there has been an increase in incidence and mortality among in those under than 50 years. Both the American Cancer Society (ACS) and the US Preventive Services Task Force (USPSTF) recommend screening for average average-risk individuals from age 45-75 in patients with a life expectancy of greater than 10 years. Although the ACS and USPSTF recommended CT colonography (CTC) as an option for colorectal cancer screening, the Centers for Medicare and Medicaid Services does not reimburse for screening CTC and cited radiation risk as a concern; specifically, insufficient evidence of risk in the Medicare-aged population (65 years). Average CTC doses have decreased from 10.2 mSv in 2004 to 9.1 mSv in 2007 and 7.6 mSv in 2011 based on worldwide survey data for diagnostic CTC protocols. Screening CTC doses decreased from 5.6 mSv in 2007 to 4.4 mSv in 2011. Since then, advances in iterative and deep learning CT reconstruction algorithms have reduced dose. However, to our knowledge, no recent CTC dose data has been published to evaluate if these advances have decreased dose reduction in CTC. The objective of this study is to investigate the CTC radiation dose trend in the American College of Radiology Dose Index Registry (ACR DIR), which solicits voluntary dose indices from facilities in the US.

Materials and Methods:
Deidentified, aggregated noncontrast CTC dose data, including CTDIvol, DLP, age, location, and hospital type, were obtained from the ACR DIR between 2012 and 2022. The effective dose was estimated by multiplying the DLP by 0.015 conversion coefficient (<em>k</em>) for the abdomen/pelvis. A linear regression model was used to calculate the dose trend over time.

Initial results demonstrate that 51,573 examinations met the criteria between 2012 and 2022. The average CTDIvol (STdev) was 16.1 mGy (14.7) in 2012 and 14.6 mGy (14.1) in 2022. This equates to an effective dose of 11.0 mSv and 10.2 mSv, respectively. Linear regression model between dose and year showed a slope of -0.1296 mGy/year (<em>R</em><sup>2</sup> = 0.0049; <em>P</em> < 0.0001), demonstrating a small decrease in dose over time.Further subgroup analysis will be performed, including evaluating trends and differences in location, type of practice, deidentified CT manufacturer, and age.

Although there is a minimal downward trend in CTC screening doses, the average doses in the ACR DIR for noncontrast CTC are higher than those published in 2011 for screening and daily practice/diagnostic protocols. The ACR DIR data are likely more reflective of the doses used in general practice in the US because the 2011 survey data were obtained only from institutions that had published CTC research as identified on PubMed. Therefore, practices in the US should be further encouraged to reduce doses by updating CT protocols to incorporate newer dose reduction algorithms.