A new study has found that women who have received radiation to treat breast cancer had increased risks of developing heart disease. The risk was linked to unintended (incidental) radiation exposure to the heart.
The researchers discovered that the higher the dose of radiation given, the higher the risk. Women with preexisting risk factors for heart disease were at greater risk after radiotherapy than women without these risk factors.
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Researchers in England conducted a large case-control study involving 2,168 female breast cancer patients treated with radiotherapy between 1958 and 2001 in Sweden and Denmark.
A total of 963 women with major coronary events and 1,205 healthy controls were included in the study. Sarah C. Darby, PhD, Professor of Medical Statistics at the University of Oxford, led the study.
Radiological charts were reviewed to determine the dosing given during treatment.
Benjamin Smith, MD, assistant professor of Radiation Oncology at The University of Texas MD Anderson Cancer Center, told dailyRx News, “This is one of the most important studies on breast cancer radiation therapy to be published in the past decade. Although radiation therapy has been shown to lower recurrence risk and improve survival, it has long been appreciated that incidental radiation to the heart during the course of radiation therapy may result in an increased risk of cardiac events and death. However, to date, little has been known regarding the time course for radiation-related cardiac events and the relationship between radiation dose delivered and cardiac risks.”
Radiation doses are measured in so-called “grays” recorded as Gy. The overall mean dose to the whole heart in this study was 4.9 Gy – with a range of 0.03 to 27.72.
Rates of major coronary events increased 7.4 percent for every gray delivered by radiotherapy, the researchers found.
Serious heart problems started appearing in study members within the first five years following treatment, and the increased risk lasted for at least 20 years.
“The implication of this finding is that there is no dose to the heart that can be considered completely 'safe'. However, it should be emphasized that the absolute excess risk of cardiac events is generally small, particularly in women receiving low doses of radiation to the heart,” Dr. Smith said.
The study explained these risks. A 50-year-old woman’s risk of dying from heart disease before age 80 would go from 1.9 percent to 2.4 percent if she had received an average dose of 3 Gy to the heart. If that woman had heart risk factors and received the same treatment, her risk of dying from heart disease before age 80 would go from 3.4 percent to 4.1 percent, according to the study.
The study found that women treated with radiation to the left breast had higher rates of major coronary events than women who received radiation to the right breast.
Dr. Smith told dailyRx News that MD Anderson uses a technique called “deep-inspiration breath hold” which delivers radiation only when the patient takes a deep breath in.
“Because the heart moves back and down during breath hold, this allows delivery of radiation to the breast without exposing the heart to radiation.” He added that “this technique can dramatically lower risk, although risk cannot be entirely eliminated as the heart still receives a low dose of radiation.”
Dr. Smith said, “Unfortunately, deep-inspiration breath hold is not widely available in the US. I hope that the data presented by Darby et al. will serve as a strong impetus for this technology to become a standard part of breast cancer treatment.”
A paper reporting the study findings was published in the March 14 issue in the New England Journal of Medicine. The research was supported by Cancer Research UK, the British Heart Foundation, the UK Medical Research Council, the European Commission, the UK Department of Health, the British Heart Foundation Centre for Research Excellence and the Oxford National Institute for Health Research Biomedical Research Centre. No conflicts of interest were disclosed.