Breast Cancer: How Proton Therapy Is Protecting Hearts

For many patients with breast cancer, radiation can be a valuable part of treatment. However, radiation for breast cancer behaves very much like a two-way street. Radiation can help save your life. And, it can also increase your risk of developing heart disease later in life.

As a result, women with advanced breast cancer have long had to weigh the pros and cons of getting radiation so close to their heart.

Here's the good news: A different type of radiation treatment could make that decision easier – proton therapy.

We took a closer look at the problem and at one of our clinical trials, which explores a new radiation treatment that significantly reduces the cardiac risk typically seen with traditional radiation.

Proton vs. Photon Radiation

Illustration of Photon Beam with exit dose
Photon beam (x-ray) - exit dose
Illustration of Photon Beam with exit dose
Proton beam (x-ray) - no exit dose

Traditional radiation, or photon radiation, is given to many breast cancer patients after their cancerous tumor has been removed. The goal of radiation is to prevent breast cancer cells from returning in that area of the body.

"In the average woman getting radiation to the breast, we feel that modern photon radiation has gotten very, very good at avoiding high doses to the heart," says Gary Freedman, MD, radiation oncologist at Penn Medicine and one of the researchers for the clinical trial. But “we are always looking to improve radiation so that we can do even better in the future.”

While the risks for injury to the heart have decreased compared to past decades, nevertheless, in some women, the heart can be more difficult to avoid if it is very close to the area beneath the left breast or if there is a need to treat lymph node areas close to the heart.

Traditional radiation uses X-ray beams to destroy cancerous tissue, but they can also kill healthy tissues along the path of the beam.

Proton beams, on the other hand, have a unique property that allows them to enter the body and deposit most of their energy at the site of the cancerous tumor, minimizing damage to nearby healthy tissue and organs. With proton therapy for breast cancer this means, on average, 60 to 70% reduction in radiation to the heart and on average more than 50% less radiation to the lung as compared with conventional radiation.

By reducing the radiation to the heart and lungs, we can in turn lower the risk of developing side effects such as heart disease, reduced lung function, or secondary cancer. This advantage may be more likely in cases where cancer has developed in the left breast, since it is situated so close to the heart.

The Roberts Proton Therapy Center at Penn Medicine currently treats:

  • Stage II and stage III breast cancer
  • Any ER, PR receptor status (positive or negative)
  • Her2Neu positive or negative

The Trouble with Lymph Nodes

Our new clinical trial will see if proton therapy reduces the cardiac risk for women being treated for breast cancer on their left side, compared to women who get traditional radiation.

Lymph nodes are glands that, along with other parts of the lymphatic system, work to clear away infections and keep the body fluids in balance. When cancer is more advanced, it may be necessary to radiate the lymph nodes close to the breasts as well.

"It's the lymph node radiation that can increase risk to the heart,” says Dr. Freedman. “Some of the lymph nodes that drain the breast are toward the underarm, which is away from the heart, but some are more inner, like toward the area next to and behind the breastbone."

So, getting to these inner lymph nodes usually brings the radiation beams very close to the heart, which can cause problems years later.

"That's the whole goal of the proton,” he adds. “To be able to treat those nodes, but do it safely and not give the woman any more risk of heart disease."

Lymph nodes aren’t the only troublesome spots. “If a radiation dose is given to the coronary artery of the heart, it increases the risk on average—even eight to 10 years later—that women can have delayed risk of heart attacks,” Dr. Freedman cautions.

Hope for Future Breast Cancer Treatment

Woman holding her hands over her heartThough considerable progress has been made in breast cancer treatment, Penn Medicine continuously works to improve the effectiveness and impact of treatment. Women who have had radiation treatments for breast cancer helped the Penn team put the study together based on the issues they were most concerned about such as heart problems after treatment and how radiation might affect the quality or length of their life.

"The trial hopes to enroll about 2,000 women being treated for left-sided breast cancer who may receive radiation close to the heart or may have a greater chance of having heart injuries from radiation," says Dr. Freedman.

Half of those women will be randomly assigned proton therapy radiation for five to seven weeks, while the other half will be given traditional radiation. Both groups will then be followed for at least 10 years after completing radiation therapy.

"What's different about this trial," he notes, "is that its major focus is on the cardiac issues and on the patient’s quality of life."

The researchers say no matter which group the women find themselves in, their doctors would work very carefully to reduce the radiation to their healthy tissues.

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The Focus on Cancer blog discusses a variety of cancer-related topics, including treatment advances, research efforts and clinical trials, nutrition, support groups, survivorship and patient stories.

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