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CT scans and cancer

December 28, 2009

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The rapidly growing use of CT scans to diagnose illness and guide treatment has heightened concern about the amount of radiation exposure people accumulate over a lifetime. Two new studies shed light on the scope of the problem: One reports that radiation doses are higher then previously believed, and vary widely from patient to patient even within the same hospital. The other estimates that in 2007 alone, 29,000 future cases of cancer could be attributed to the 72 million CT scans performed that year.

Researchers led by Dr. Rebecca Smith-Bindman of the University of California-San Francisco tracked radiation doses given to more than 1,000 people during CT scans at four hospitals in the Bay Area. The doses they measured in some cases averaged four times higher than commonly quoted in national guidelines. They also found radiation doses used for the same type of CT scan were as much as 13 times stronger in one patient compared with another. Based on what they measured, the authors estimate that 1 in 270 women and 1 in 600 men who had CT scans of their hearts at age 40 would later develop cancer. For head scans at age 40, the risk was lower: 1 in 8,100 women and 1 in 11,080 men. For 20 year-olds, the lifetime risks were twice as high.

Amy Berrington de González of the National Cancer Institute and her colleagues compiled estimates of future cancer risk from scans performed in 2007. Based on previous research linking radiation exposure to cancer risk, they arrived at 29,000 projected cancer cases. Half of those cancers would lead to death, they estimated.

BOTTOM LINE: The amount of radiation patients receive from CT scans is higher than previously thought, varies widely, and contributes to cancer risk that could lead to as many as 29,000 future cancer cases from one year’s exposures.

CAUTIONS: The first study was too small to determine why radiation doses varied; possible reasons include technologist experience or differences among patients. The second study noted that cancer risks from CT scans have not been demonstrated directly, although radiation itself is linked to cancer.

WHERE TO FIND IT: Archives of Internal Medicine, December 14/28

Skin aging linked to smoking and weight

Aging skin is mostly a product of genetic factors, but up to 40 percent of the changes that make skin look old, including coarse wrinkles, pigment spots, and dilated blood vessels, come from sun damage and other environmental causes, research has shown. A team from Case Western Reserve University School of Medicine visited the annual Twins Day Festival in Twinsburg, Ohio, to look at factors other than genes shared by twins that might affect skin aging.

Kathryn J. Martires led a team that surveyed 65 pairs of twins about their history of skin cancer, smoking and drinking habits, and weight. Clinicians scored sun damage to the skin on their faces, grading wrinkles and changes in pigmentation. Extent of sun damage was more similar between identical twins than fraternal twins, though the difference was not statistically significant. Those who smoked and were overweight were more likely to have sun damage, and those who drank alcohol were less likely to have sun damage, than their twins.

BOTTOM LINE: A history of being overweight and smoking cigarettes was linked to sun damage and aging of skin on the face among twins.

CAUTIONS: The study depended on twins’ reports of their health and habits, which could be inaccurate.

WHERE TO FIND IT: Archives of Dermatology, December


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