What heart disease risks come from what specific doses isn’t known. The new study, led by Dr. Sarah Darby of the University of Oxford in England, sought to measure that.
It involved 2,168 breast cancer patients from Sweden and Denmark diagnosed between 1958 and 2001 and treated with radiation. They included 963 women who suffered a heart attack, needed an artery-opening procedure or died of heart artery-related causes in the years after their radiation treatment. The other 1,205 were similar patients who did not develop these heart problems.
Researchers compared the women’s radiation exposures using gray units, a measure of how much is absorbed by the body. They used hospital records and treatment plans to figure how many gray units actually reached each woman’s heart and one artery often involved in heart attacks.
Most women treated today get doses that result in 1 to 5 gray units reaching the heart — more if the cancer is in the left breast. Patients in the study got an average of five gray units; the doses ranged from 1 to 28.
The risk of a heart attack, need for an artery-opening procedure or dying of heart disease rose about 7 percent per gray unit and no “safe” level was seen. The risk started to rise within five years of treatment and continued for at least 20 years.
What to do?
Don’t forgo radiation if it’s recommended because it is lifesaving and doctors increasingly have ways to shield the heart from exposure, said Dr. Bruce Haffty, associate director of the Cancer Institute of New Jersey and president-elect of ASTRO, the American Society for Radiation Oncology.
“Whatever cardiac risks may be there, they are outweighed by the cancer benefit,” he said.
Some centers have special tables that women lie on face-down with holes for the breast to hang through. That allows radiation to be delivered just to that tissue rather than the wider chest area that gets irradiated when a woman lies face-up on a table.
Women need to tell any doctor treating them about radiation they have received in the past. It may mean they should avoid diagnostic tests that use radiation and instead have ultrasounds and MRI, or magnetic resonance imaging, whenever possible, Slosky said.
Some places are starting to use electronic medical records to track radiation exposure over a patient’s lifetime, so the cumulative dose is known regardless of who ordered what test and when.
“I’d like to have a personal record like a personal dosimeter” for each patient, Slosky said. “Then you’d know” what risks they face and what tests are safe for them in the future.