TUESDAY, Nov. 16, 2010 (HealthDay News) -- The potential cancer risk that radiation from mammograms might cause is slight compared to the benefits of lives saved from early detection, new Canadian research says.
The study is published online and will appear in the January 2011 print issue of Radiology.
This risk of radiation-induced breast cancers "is mentioned periodically by women and people who are critiquing screening [and how often it should be done and in whom]," said study author Dr. Martin J. Yaffe, a senior scientist in imaging research at Sunnybrook Health Sciences Centre and a professor in the departments of medical biophysics and medical imaging at the University of Toronto.
"This study says that the good obtained from having a screening mammogram far exceeds the risk you might have from the radiation received from the low-dose mammogram," said Dr. Arnold J. Rotter, chief of the computed tomography section and a clinical professor of radiology at the City of Hope Comprehensive Cancer Center, in Duarte, Calif.
Yaffe and his colleague, Dr. James G. Mainprize, developed a mathematical model to estimate the risk of radiation-induced breast cancer following exposure to radiation from mammograms, and then estimated the number of breast cancers, fatal breast cancers and years of life lost attributable to the mammography's screening radiation.
They plugged into the model a typical radiation dose for digital mammography, 3.7 milligrays (mGy), and applied it to 100,000 hypothetical women, screened annually between the ages of 40 and 55 and then every other year between the ages of 56 and 74.
They calculated what the risk would be from the radiation over time and took into account other causes of death. "We used an absolute risk model," Yaffe said. That is, it computes "if a certain number of people get a certain amount of radiation, down the road a certain number of cancers will be caused."
That absolute risk model, Yaffe said, is more stable when applied to various populations than relative risk models, which says a person's risk is a certain percent higher compared to, in this case, those who don't get mammograms.
What they found: If 100,000 women got annual mammograms from ages 40 to 55 and then got mammograms every other year until age 74, 86 breast cancers and 11 deaths would be attributable to the mammography radiation.
Put another way, Jaffe said: "Your chances are one in 1,000 of developing a breast cancer from the radiation. Your changes of dying are one in 10,000."
But the lifetime risk of breast cancer is estimated at about one in eight or nine, he added.
Due to the mammogram radiation, the model concluded that 136 woman-years -- that's defined as 136 women who died a year earlier than their life expectancy or 13 women who died 10 years earlier than their life expectancy -- would be lost due to radiation-induced exposure. But 10,670 woman-years would be saved by earlier detection.
The data to estimate deaths from radiation exposure was gathered from other sources, such as from patients who received radiation from the nuclear weapons used in Japan. "We really don't have any direct evidence that any woman has ever died because of radiation received during the mammogram," Yaffe said.
"I'm not minimizing the concern of radiation," Rotter said. "Everything is a balance." For example, younger breasts, particularly those of women aged 40 to 49, are more sensitive to radiation than breasts in older women, but the new study shows it's better to get the screening mammography than skip it.
To learn more about mammography, visit the American College of Radiology.