Are CT Scans Sometimes Too Risky?
Study Shows Radiation Doses From CT Scans Vary Widely
Dec. 14, 2009 -- Radiation doses from CT scans are often high and vary
widely, and excessively high doses may contribute substantially to future
cancers, a study shows.
CT scans are noninvasive medical tests that combine special X-ray equipment
and computers to produce detailed cross sectional images of the body. The
number of CT scans performed has exploded over the last three decades, growing
from about 3 million yearly in 1980 to about 70 million in 2007.
The new study is published in the Archives of Internal Medicine.
Study researcher Rebecca Smith-Bindman, MD, of the University of California San
Francisco, says the idea for the research began "when I was looking at some
individual scans; I was surprised at how high the radiation dose was. I thought
it was time to start looking."
The new research comes in the wake of the discovery earlier this year that
more than 200 stroke patients at Cedars-Sinai Medical Center in Los Angeles had
received more than eight times the necessary radiation dose when undergoing CT
scans. That, in turn, prompted the FDA to encourage CT facility personnel to
review their protocols and be sure the values displayed on the control panel
jibe with doses normally associated with the scan being performed.
In Smith-Bindman's study, researchers evaluated radiation doses given to
1,119 patients getting CT scans and found that ''the differences in radiation
exposure were dramatic," she says. "The doses are on one hand higher than they
should be, but also the variation [for the same procedure] is much higher than
it should be."
The message from her research, Smith-Bindman says, is for doctors and
patients not to panic but to become more aware of the issues. She says the
findings also point to the need for more oversight of the scans.
Radiation From CT Scans
Smith-Bindman and her team evaluated CT scan patients who were getting care
at four San Francisco area facilities in 2008. They calculated the radiation
dose involved with each scan.
The doses varied widely between the different types of scans. The median
doses (half higher, half lower) ranged from 2 millisieverts (the measures of
radiation used in CT scans) for a routine head CT scan to 31 millisieverts for
a multiple-phase abdomen and pelvic scan.
The dose ranges were high. For example, for a head CT scan, while the median
dose was 2, the range was 0.3 to 6. "'That is a huge range," she says.
Most dramatic, she says, was the dose and the dose range for a multiphase
abdomen and pelvic series. While the median dose was 31, the range was from 6
Then the researchers estimated the lifetime cancer risk linked to the CT
scan. They estimated that one in 270 women and one in 600 men who got a CT
coronary angiogram at age 40 would develop cancer from that scan. They also
estimated that one in 8,100 women and one in 11,080 men who had a routine head
CT scan at age 40 would develop cancer.