Protons may lower risk of radiation-related heart disease among breast cancer patients

If only Dr. Julie Bradley could speed up time, she would confirm what she suspects: Breast cancer survivors treated with protons will be much less likely to die from heart disease than those treated with photon radiation.

But Bradley is no wizard.

She’s a radiation oncologist at the University of Florida Proton Therapy Institute in Jacksonville, Florida. And she and other researchers are working to find clear signs that indicate harm to the heart caused by unintentional irradiation — many, many years before that harm finally plays out as heart disease.

“What can we do to identify anything earlier, some kind of cardiac biomarker, and not have to wait five or 10 years?” Bradley asked. “Is it identified by imaging or by a lab test? We don’t know yet.”

If they succeed, cancer researchers may be able to compare the incidence of such cardiac biomarkers among breast cancer survivors treated with photon radiation and those treated with proton radiation. The possible scarcity of such biomarkers among proton patients would demonstrate a clear clinical advantage for protons in treating some breast cancers.

“Cardiac disease or death is 5 to 15 to 20 years down the road for many cancer survivors treated with photons,” Bradley said. “We tend to see higher heart doses in photon radiation plans for regional nodal breast cancer and left-sided breast cancer. And over time, we’ve seen an increase of cardiac death among those cancer survivors.”

Bradley and other proton therapy specialists predict that five or 10 years after successful treatment with surgery and protons, breast cancer survivors will show a lower incidence of cardiac death. And that waiting is what frustrates Bradley. “If we can identify that earlier, rather than waiting 10 years, we can help people a lot earlier using protons,” she said.

Until those biomarkers are discovered, clinicians like Bradley are gauging which types of breast cancers are optimal for proton beams primarily based on reduced radiation exposure to the heart and lungs.

“We’re doing lots of work to define which breast cancer patient populations are best treated with protons,” said Bradley. “Women at risk for lymph node involvement are one major group. Left-sided breast cancer patients are another. In looking at the literature, the increase in heart disease is really reported for left-sided breast cancer patients treated with photons.

“Women who have a family history of cardiac disease are another group we think would benefit from protons,” Bradley continued. “You don’t want to add another cardiac risk factor like unintended photon radiation. Finally, there is a group of women who have chest walls shaped in such a way that it makes it hard to avoid the heart with any kind of radiation. We think protons may be best for each of these groups.”

Bradley recently presented preliminary findings of a pilot study of 11 women with breast cancer, aged 42 to 73, who, after surgery, underwent proton treatment of regional lymph nodes. The unintended radiation dose to the heart was significantly decreased by using protons, Bradley said.

According to an abstract of the pilot study published in the International Journal of Radiation Oncology, the median mean heart dose from unintended proton radiation was 86 percent lower than the unintended photon radiation dose.

“Proton and conventional radiation treatment plans were developed for each patient,” Bradley reported. “The superior plan, as defined by organ-at-risk-sparing and target coverage, was used to deliver the radiation. For all 11 patients, the proton plan better met dosimetric goals and, therefore, was used for treatment delivery.”

Bradley hopes to expand the study to include as many as 24 breast cancer patients. More information can be found at clinicaltrials.gov.