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Risk and Risk Reduction of Major Coronary Events Associated With Contemporary Breast Radiotherapy
Study Questions:
Does the radiation treatment plan for breast cancer influence subsequent risk for coronary events?
Methods:
Prospectively collected data from 48 patients with stage o to IIA breast cancer were collected for this analysis. All data were collected after 2005 at New York University Department of Radiation Oncology. Two treatment plans, for supine and for prone treatment positions, were generated for each patient. The risk estimates were based on contemporary patient-specific radiation doses averaged over the cardiac volume (hereafter, mean cardiac dose). Absolute risk of radiotherapy-induced major coronary events (myocardial infarction, coronary revascularization, or death from ischemic heart disease) were calculated for each patient, on the basis of patient-specific mean cardiac doses and using the dose-response relationship. Baseline risk was calculated (using the Reynolds algorithm) for each patient; patients were then grouped into low-risk, medium-risk, and high-risk. Cardiac risks were calculated over 20 years after radiotherapy, the approximate mean life expectancy after early-stage breast cancer.
Results:
For standard supine-positioned radiotherapy, the patient-averaged mean cardiac dose was 1.37 (95% confidence interval [CI], 1.12-1.61) Gy (to convert to rad, multiply by 100), less than one-third of the average mean cardiac dose reported for breast radiotherapy from 1958 to 2001. Mean cardiac doses were significantly lower for right-sided than for left-sided breast radiotherapy. For left-sided (but not right-sided) radiotherapy, treating in a supine position resulted in a halving of the mean cardiac dose. The highest estimated radiotherapy-induced risks were for left-sided radiotherapy in high–cardiac risk women treated in the supine position (3.52% [95% CI, 1.47%-5.85%]), whereas the lowest risks were for right-sided radiotherapy in low–cardiac risk women (<0.1%).
Conclusions:
The authors concluded that estimated lifetime risks of major coronary events for patients who receive radiotherapy for breast cancer are now in the range from 0.05% to 3.5%, with a typical value of 0.3% for a typical scenario. The highest cardiac doses and excess cardiac risks result from supine positioning during left-sided radiotherapy; for left-sided radiotherapy, prone positioning significantly reduces cardiac doses and risks.
Perspective:
These data provide useful information for women undergoing radiation therapy for breast cancer. Women with traditional risk factors at baseline may benefit from changes in radiation position (prone vs. supine) and aggressive management of traditional risk factors. Further research in this area is warranted.
Keywords: Risk, Myocardial Infarction, Radiation Oncology, Myocardial Ischemia, Risk Reduction Behavior, Life Expectancy, Prone Position, Breast Neoplasms, New York, Supine Position, Cardiac Volume, Cardiovascular Diseases, Confidence Intervals
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