PHILADELPHIA - The age and gender of patients are significant determining variables in calculating the risk of radiation-induced cancer from body CT scans, with young women at highest risk, according to research presented Monday at the American Association of Physicists in Medicine (AAPM) annual meeting.
Researchers from Clemson University in Clemson, SC, and the Medical University of South Carolina in Charleston found that women have a 26% higher cancer risk per millisievert (mSv) than men. They also found that 80-year-old male patients have a fivefold decrease in radiation-induced cancer risk compared to their 20-year-old counterparts, while 80-year-old female patients have a nearly sixfold decrease in risk.
Wenjun He from Clemson presented the research team's findings during a scientific session at the meeting, held this week in Philadelphia.
With the increase in procedures and level of radiation exposure from CT, it's increasingly important to make sure that benefits of body CT scans outweigh the risks for patients, He said.
Seeking to compare radiation-induced cancer risks per mSv in body CT studies, the researchers investigated chest, abdominal, and pelvic CT examinations. Eight CT scanners were used, including two each from GE Healthcare (Chalfont St. Giles, U.K.), Siemens Healthcare (Malvern, PA), Philips Healthcare (Andover, MA), and Toshiba America Medical Systems (Tustin, CA).
Effective doses and organ doses were obtained using version 1.0 of the ImPACT CT patient dosimetry calculator. Organ doses were then converted into gender- and age-dependent carcinogenic risks using data from the Biological Effects of Ionizing Radiation (BEIR) VII report, according to He.
Based on these findings, 20-year-old females have a 2.5 times higher risk for cancer from body CT scans than 20-year-old males. This difference drops with age to less than two times the risk for 80-year-old females compared with 80-year-old males.
By specific scan types, data from chest scans showed that women ages 20 to 80 have a 2.6:1 higher overall risk of cancer, He said. At the age of 20, the risk is approximately 3.5 times higher for females than for males.
Gender differences were minimal with abdominal scans, however. And the tables were turned somewhat in pelvic scans, with females having a 0.89:1 risk of cancer compared with males.
Looking further at age differences for cancer risk from 1 mSv of radiation, a 20-year-old female had the highest cancer risk from a chest CT scan of 17.3 per 100,000 people. This risk drops to 5.89 per 100,000 people for a 60-year-old female.
Other findings for a 20-year-old female include a cancer risk from a pelvic scan of 13.3 per 100,000 people and a risk of 6.5 per 100,000 people for an abdominal scan. Pelvic scans, however, were the riskiest for a 40-year-old male.
"In body CT, when [examining] fixed age and gender, the risk per mSv varies between 200% and 300%," she said.
By Erik L. Ridley
AuntMinnie.com staff writer
July 20, 2010
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