Coronary Risk Varies by Breast-Cancer Radiotherapy Technique

October 29, 2013

NEW YORK, NY — Estimated 20-year risk of "major coronary events" stemming from radiotherapy of early-stage breast cancer was highly dependent on whether therapy was delivered from the right or left side, with the patient in the supine or prone position, and especially on patient baseline cardiovascular risk status, in a small prospective study[1].

Left-sided radiotherapy in supine-positioned patients, especially those with high baseline risk status, posed the greatest risk in the analysis. Prone-positioned patients treated from the right side (the fields exclude the heart), especially those with low baseline risk, had the lowest estimated risk. The analysis from Dr David J Brenner (Columbia University Medical Center, New York, NY) and colleagues is published online October 28, 2013 as a research letter in JAMA Internal Medicine.

In light of the pronounced effect of Reynolds-score baseline risk status on late coronary risk, the group proposes that "radiotherapy-induced risks of major coronary events [would] likely to be reduced in these patients by targeting baseline cardiac risk factors (cholesterol, smoking, hypertension), by lifestyle modification, and/or by pharmacological treatment."

The group estimated risks related to radiation dosing by direction and body position based on a historical series of women receiving breast radiotherapy from 1958 to 2001. They prospectively applied those estimates to two radiotherapy treatment plans, based on the patient in supine and prone positions, devised for 48 women with stage 0 through IIA breast cancer.

Their findings:

  • Estimated mean cardiac radiation dose from the left side was 2.17 Gy with the patient in the supine position and 1.03 Gy for the patient in prone position.

  • With right-sided radiation, estimated doses were 0.62 Gy and 0.64 Gy for supine and prone positioning, respectively.

  • For treatment from the right or left side, the excess risk of coronary events (MI, coronary revascularization, death from ischemic heart disease) rose with rising baseline CV risk.

  • For treatment from the left side, prone vs supine positioning consistently lowered coronary risk, regardless of baseline risk.

  • For treatment from the right side, the excess coronary risk was similar for supine and prone positioning at each baseline-risk level.

  • Differences in radiotherapy side and body position most influenced coronary risk among patients with a high baseline risk.

Estimated Patient-Averaged Lifetime Excess Coronary Risk (95% CI) Associated with Contemporary Breast Cancer Radiotherapy, by Baseline CV Risk

Radiation delivery, body position Low baseline CV risk High baseline CV risk
Left side, supine 0.22 (0.08–0.36) 3.52 (1.47–5.85)
Left side, prone 0.09 (0.05–0.13) 1.31 (0.86–1.86)
Right side, supine 0.05 (0.03–0.07) 0.79 (0.57–1.06)
Right side, prone 0.06 (0.03–0.08) 0.84 (0.57–1.18)

*Coronary risk=20-year risk of MI, coronary revascularization, or death from ischemic heart disease

"In breast-cancer radiotherapy today, there is considerable variability in the dose received by the heart and in the extent of preexisting risk of ischemic heart disease. Thus, there is likely to be considerable variability in the cardiac risks of radiotherapy," write Drs Carolyn Taylor and Sarah C Darby (University of Oxford, UK) in an accompanying commentary[2]. It was their group's analysis of historical data on which the current dosing-risk estimates were based.

"Our dose-response relationship can be used to provide reassurance for the majority of women that their absolute risk of ischemic heart disease from breast-cancer radiotherapy is likely to be small compared with the likely absolute benefit from radiotherapy. It can also be used to identify the minority of women for whom the benefits of radiotherapy do not clearly outweigh the risks, including those for whom adequate coverage of the target tissue cannot be achieved without a high heart dose."

Neither Brenner et al nor Taylor and Darby had disclosures.

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