Radiation for breast cancer is an important treatment known to reduce the risk of the cancer returning and death from the disease. It’s usually given after breast-conserving surgery and sometimes after mastectomy, as it is a key component to breast cancer therapy. However, a new study found that beams of radiation can penetrate beyond the breast to the heart and the arteries that feed it. According to the Huffington Post, the research suggests that women treated with radiation for breast cancer are more likely to develop heart problems later in life, even 20 years after the end of the treatment.

Each year, more than 232,000 American women will be diagnosed with breast cancer. Although there are an estimated three million survivors today, treatments have been linked to heart health risks. Chemotherapy drugs are known to harm the heart muscle, but the new study shows radiation can hurt arteries, making them prone to harden, clog and cause a heart attack.

Researchers at the University of Oxford in England evaluated the magnitude of the risk associated with radiation exposure to the heart. In a study of 2.168 breast cancer patients from Sweden and Denmark who were diagnosed between 1958 and 2001 and treated with radiation, doctors found that any amount of radiation increased the risk of heart disease. Of the participants, 963 women suffered a heart attack, needed an artery-opening procedure or died of heart-artery related causes in the years after their radiation treatment. The remaining participants did not develop these heart problems.

Over the course of 20 years, the risk of heart disease increased an average of 7.4 percent with each additional unit of radiation, which is called a gray. Although new technology allows doctors to reduce exposure to a fraction of one gray, American women often receive radiation of about 2 to 5 gray to the heart. Furthermore, women who received radiation to the left breast, which is closer to the heart, were at especially high risk, along with women who had pre-existing heart disease.

Despite the findings, doctors maintain that patients should not avoid potentially lifesaving radiation therapy because of the risk of heart disease. The cardiac risks are outweighed by the benefits of removing the cancer, and many centers are discovering ways to shield the heart from exposure. Special tables that allow women to lie face-down with holes for the breasts to hang through help deliver radiation to the targeted tissue more effectively. There’s also radiation therapy that is synchronized with patient breath and stops the radiation beam automatically as women breath in and out to nearly eliminate exposure to the heart.

Yet the study still raises concerns about the need to do more to prevent risks with breast cancer treatments. Although the study did not look at all types of heart problems linked with radiation therapy, nor did it consider chemotherapy, women should be aware of heart disease risks after radiation treatment to the breast. Patients can help cut their risk by keeping weight, cholesterol and blood pressure under control, and doctors should identify women with pre-existing heart disease risk factors, in addition to tracking radiation exposure over each patient’s lifetime. Dr. Carolyn Taylor, who led the study, explains that despite improvements in radiation machines, women should still be aware of risks: “This study has shown for the first time that as the radiation dose to the heart increases, so does the risk of radiation-induced heart disease.”