Among patients with early stages of breast cancer, the risk of heart disease is higher for those whose hearts were more directly irradiated with radiation treatments on the left side in a facing-up position.

Several reports have suggested links between breast cancer radiation and long-term cardiovascular-related deaths, according to the study background. As survival rates have improved, minimizing long-term complications from treatment has become increasingly important.

Researchers, led by David J. Brenner, PhD, DSc, of Columbia University Medical Center in New York, New York, examined the radiation treatment plans of 48 patients with stage 0 through IIA breast cancer who were treated after 2005 at the New York University Department of Radiation Oncology. They calculated the association between radiation treatment factors, such as mean cardiac dose, cardiac risk, treatment side, body positioning, and coronary events.

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According to study results, the highest coronary risks were seen for left-sided treatment in women of high baseline risk treated in the supine (face up) position. The excess risk was 3.52 for these patients in the highest category of baseline risk. Baseline risk was age-dependent and based on the standard Reynolds algorithm.

The lowest risks were for right-sided treatment in low-baseline risk women, with the patients in the highest category of risk having an excess risk of 0.84 in the prone position. In left-sided radiation, prone (face down) position reduces cardiac doses and risks, while body positioning has little effect in right-sided therapy (where the heart is always out of the field). The study was published in JAMA Internal Medicine (2013; doi:10.1001/jamainternmed.2013.11790).

“Because the effects of radiation exposure on cardiac disease seem to be multiplicative, the highest absolute radiation risks correspond to the highest baseline cardiac risk,” the authors concluded. “Consequently, radiotherapy-induced risks of major coronary events are likely to be reduced in these patients by targeting baseline cardiac risk factors (cholesterol, smoking, hypertension), by lifestyle modification, and/or by pharmacologic treatment.”