Study compares organ-sparing properties of protons with other breast cancer treatments

A recent study showed proton therapy to be superior to three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and helical tomotherapy (HT) in sparing the heart and coronary arteries from unintended radiation when treating Stage III breast cancer.

“The study validates what we had hypothesized, which is that with the use of proton therapy, we can greatly reduce radiation exposure to the heart, lung and contralateral [opposite] breast,” said L. Christine Fang, M.D., one of the study investigators and a physician at Seattle Cancer Care Alliance Proton Therapy, A ProCure Center.

Because more normal tissue can be spared from unintended radiation with proton therapy, using it with breast cancer patients allows delivery of a more optimal dose. “When we are designing very complicated treatment plans with conventional 3D conformal therapy, we have to compromise on how much dose is delivered to the areas we care about — the chest wall, the lymph nodes — because the dose to the heart and the lung would otherwise be excessive,” said Dr. Fang. “For example, in order to get a certain dose to the lymph nodes, the lung or heart may receive unacceptably high doses, so we make the decision to lower the dose to the lymph nodes.

“With proton therapy, because we’re able to decrease exposure to the normal tissue, we will not need to make that hard decision to compromise on the dose to the chest wall and lymph nodes. That’s the great thing. When we run plan comparisons, not only do we look at the difference between doses to the heart, lung and contralateral breast, but we also look at how well the target areas are covered by the radiation dose. Proton plans more adequately cover the target than the other modalities.”

Presented at the 2013 American Society for Radiation Oncology Annual Meeting, the study involved 10 women ranging in age from their early 30s to their early 70s. All had had a left mastectomy and had received conventional 3D-CRT with photons. Then, proton, IMRT and HT treatment plans were prepared for each patient, after which important metrics for dose levels of unintended radiation exposure to heart, lung and opposite breast were compared.

In the study, 3D-CRT, IMRT and HT delivered an average radiation dose to the heart that was seven to 10 times higher than the dose delivered by proton therapy. The dose delivered to the contralateral breast was eight to 30 times higher for the other three modalities than with protons. Lung dose was also higher with 3D-CRT, IMRT and HT than with protons, said Dr. Fang.

A Phase II study of postsurgical, cardiac-sparing proton radiotherapy for women with Stage III breast cancer is now under way at ProCure Proton Therapy Centers in Warrenville, Illinois, and Somerset, New Jersey. Click on either link, then on Clinical Trials for more information on these studies and to see if you are eligible, or click here. In 2014, a similar study will be opened at the SCCA Proton Therapy center in Seattle, Dr. Fang noted.