Proton Radiation Therapy for Left Sided Breast Cancer

Proton radiation is an advanced form of radiation that can be utilized to protect normal tissue from unnecessary radiation, while still delivering a high dose of radiation to the tumor. Proton centers have existed in the US for many years however they are very expensive to build (>100M USD) and consequently their uses have been limited. The FDA approved proton therapy for treating cancer in 1988.

Historically, it did not appear that there was a significant benefit to treating breast cancer with protons. However, this is changing. With the publication of the study by Darby et al. “Risk of Ischemic Heart Disease in Women after Radiotherapy for Breast Cancer” in the New England Journal of Medicine in 2013 Radiation oncologists are seeking more advanced treatment options to protect a woman’s heart from unnecessary radiation.

In my practice, I consider proton irradiation for women with left-sided breast cancer who need coverage of the breast (or chest wall after mastectomy) as well as the surrounding lymph nodes that drain the breast (under the arm, above the collarbone, and sometimes the lymph nodes that run along the sternum).

Here is a photo of a woman’s radiation planning scan that shows the challenge of trying to avoid the heart (pink). This patient has undergone a mastectomy and will need the chest wall treated as well as lymph nodes.

Traditional planning guidelines limit mean heart dose to < 4Gy for breast plans, however, newer guidelines are to keep the dose to < 2Gy. Of note, radiation dose is measured in “gray” like the color. The chest wall in the plan above will need to receive approximately 50Gy so it’s tricky to avoid the heart with conventional radiation.

Dr. Shannon MacDonald at Harvard Medical School published the first study looking at the ability to spare the heart with protons. In the image, below the proton plan is on the far right. You can see the benefits.

Figure 1
Axial images at the level of the heart for photon/electron plan (left), partially wide tangent fields (middle), and protons (right)

In my practice, I not only check the mean heart dose, but the amount of radiation received by the left ventricle (part of the heart that pumps blood to the rest of the body) as well as a major artery called the left anterior descending or “LAD”. The LAD is known as the “widow-maker” as the LAD supplies blood to a large portion of the heart and damage to this artery can put the patient at risk of a heart attack and death.

With more and more research examining the risk of radiation to the heart, I encourage patients to speak to their radiation oncologist about their radiation plan. It is important for any patient to understand their risks of long-term side effects and how their doctor plans to minimize those risks. Fortunately, radiation planning techniques have advanced to the point where there are options to mitigate the risk of cardiac damage.