Aabed Meer, Presenter: Nothing to Disclose

Pat Auveek Basu MD, Abstract Co-Author: Nothing to Disclose

Laurence Baker, Abstract Co-Author: Nothing to Disclose

Scott W. Atlas MD, Abstract Co-Author: Nothing to Disclose

To analyze the distribution as well as amount of ionizing radiation delivered by CT scans and estimate the cancer risk from these examinations, focusing on the well-characterized patient group most frequently imaged.

We conducted a retrospective cohort study using Medicare claims for the eight years from 1998 through 2005 to assess CT usage. The data was analyzed in two temporally differentiated cohorts, 1998-2001 (N = 5,267,230) and 2002-2005 (N = 5,555,345). For each cohort, we analyzed the number and types of CT scans that each patient received to determine the percentage of patients exposed to threshold radiation doses of 50-100mSv (defined as low) and greater than 100mSv (defined as high). We used BEIR VII models to estimate the number of cancers induced by these examinations.

CT scans of the head (25% of the first cohort and 30% of the second cohort) were the most common examinations in both groups. However, abdominal imaging delivered the greatest proportion of radiation, accounting for approximately 40% of the total radiation in each cohort. Pelvis and chest imaging represented the second and third largest sources of radiation. In the 1998-2001 cohort, 42% of patients received CT scans, with 2.2% and 0.5% receiving radiation doses in the low and high ranges, respectively. In the 2002-2005 cohort, 49% of patients underwent CT scans, with 4.2% and 1.2% receiving doses in the low and high ranges, respectively. Cancer incidences related to ionizing radiation from CT were estimated to be 0.02% and 0.04% of the two populations, respectively.

The number of patients receiving radiation doses in the low and high ranges both roughly doubled from the 1998-2001 cohort to the 2002-2005 cohort. This rise is consistent with the increasing use of high-speed CT scanning in patient diagnosis and management. However, our estimates of CT-related cancer incidences are still very low, even though our study focuses on the very group of patients (older adults) receiving most CT examinations. Our data indicates a significantly lower risk of developing cancer from CT than previous estimates of 1.5 to 2% in the general population.

While the risk of secondary cancers appears to be low, the increasing reliance on CT scans underscores the importance of monitoring CT utilization and its consequences.

Meer, A, Basu, P, Baker, L, Atlas, S, Exposure to Ionizing Radiation and Estimate of Secondary Cancers in the Era of High Speed CT Scanning.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9004767.html