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Lying face down for radiation therapy lessens the amount of collateral damage to breast cancer patients' heart and lungs, researchers found.

Compared with lying on their backs, receiving radiation while in the prone position was associated with about an 86% reduction in the amount of lung tissue irradiated in women with cancer in the right breast, and a 91% reduction for women with cancer in the left breast, according to Silvia Formenti, MD, of New York University in New York City, and colleagues .

Left breast cancer patients also had about an 86% reduction in radiation to the heart, they reported in a research letter in the Sept. 5 issue of the Journal of the American Medical Association.

"If prone positioning better protects normal tissue adjacent to the breast, the risks of long-term deleterious effects of radiotherapy may be reduced," they wrote.

Whole-breast radiotherapy has been linked with damage to the heart and lung, increased cardiovascular mortality, and development of lung cancer when patients are treated in the supine position, the researchers wrote.

But early data have shown that prone positioning may mitigate some of that risk, without detracting from efficacy of breast cancer therapy.

Formenti and colleagues conducted a prospective trial at their hospital among patients with stage 0-to-IIA breast cancer. They enrolled 200 patients from with cancer of the left breast, and 200 with cancer of the right, from 2005 to 2008.

The mean age was 56.3, the majority of patients (80%) were white, and 21.5% of patients had ductal carcinoma in situ. Among the rest of the patients with invasive breast cancer, about 15% had involved sentinel or axillary lymph nodes.

For all patients, having radiation in the prone position was associated with less radiation to the lung compared with being supine.

For patients with cancer in the right breast, the mean difference in irradiated lung volume with prone radiation was 104.6 cm³ (95% CI 94.26 cm³ to 114.95 cm³), which translated to an 86.2% reduction in exposed lung tissue.

For those with left breast cancer, the mean difference was 89.85 cm³ compared with supine radiation (95% CI 80.16 cm³ to 99.55 cm³), a 91.1% reduction, they reported.

Also for left breast cancer patients, prone positioning was associated with a reduction in in-field heart volumes compared with supine positioning, with a mean difference of 7.5 cm³ (95% CI 5.16 cm³ to 9.85 cm³), translating to an 85.7% reduction in irradiated heart tissue.

But the researchers cautioned that in 15% of left breast cancer patients, the supine position was actually associated with less in-field heart volume compared with prone positioning (mean difference 6.15 cm³, 95% CI 2.97 cm³ to 9.33 cm³). They didn't offer an explanation for the difference.

They noted that all of the reductions were statistically significant regardless of breast volume, with the exception of heart tissue in women with breast size below 750 cm³.

The study was limited because it was conducted at a single institution, and a multi-institutional, prospective trial would be needed to confirm the findings, the researchers said.

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