While radiation is highly effective at killing any lingering cancer cells in or around the breasts, it can also do damage to the lungs and the heart, especially if the left breast is being treated.
When radiation causes some scarring in the lungs, it’s not a serious problem since the rest of the lung tissue can function normally and make up for any scarring. With the heart, it’s a different story because you only have one heart and it’s not like if you damage one part, the other part can take over. So protecting the heart from damage due to radiation is a high priority.
The difficult part is that problems with the heart may not show up until several years, or even decades, after radiation therapy is completed. And the issue is further complicated because there are other factors that can contribute to heart problems, such as high cholesterol and hypertension.
For many years, we had very generalized rules about how much radiation the heart could take, but it was very generous. But as we’ve gotten more information about the potential harm that can be done, we’ve worked to make the treatment safer for the heart and lungs.
One way we’re making radiation safer for these organs is by having patients lie down in the prone (face down) position while they’re undergoing radiation therapy. What this does is it allows the breast to fall away from the heart and lungs so that radiation is less likely to reach those organs. The prone position is not the standard of care for all patients with breast cancer, however. It works best with patients who have larger, more pendulous breasts.