Dear Doctor: A close relative had extensive radiation therapy for an early breast cancer. The treatment was effective, but it damaged the surrounding tissues, including her aortic valve. What are the potential side effects of radiation therapy?

Dear Reader: Radiation therapy, also known as radiotherapy, is a type of cancer treatment that uses intense beams of energy to kill cancer cells. Most often, it uses X-rays, a type of electromagnetic radiation, but a newer type of therapy uses protons. These are subatomic particles that carry a positive charge. Although both approaches to radiation therapy are effective at killing cancer cells, each can cause a range of side effects. These vary from person to person and depend not only on the type and location of a person’s cancer, but also on their general health as well.

Unlike chemotherapy, which is systemic, radiation therapy is a highly localized treatment. A person’s tumor is mapped, and the beams of energy are precisely focused on the area. Even so, surrounding healthy tissues are often damaged. Due to the physical properties of protons, that type of radiotherapy can be successful at sparing surrounding tissues. However, proton therapy isn’t widely available and can’t be used for all cancers. Radiation therapy with X-rays, while successful at killing cancer cells, can also cause damage to healthy tissues.

Radiation therapy sessions last about 15 minutes and are not painful. Treatment is administered five days a week and lasts from three to nine weeks, depending on the cancer. The energy used to kill the cancer cells is quite powerful and, over time, the nearby healthy tissues tend to sustain damage. This results in a range of side effects. A common one is fatigue, which begins during the course of treatment and can persist for several weeks or months after treatment has ended. Many people develop skin problems such as dryness, itching, blistering or peeling in the site where the radiation is delivered. Depending on the part of the body receiving the treatment, additional side effects can include swelling, or edema; hair loss; nausea; trouble swallowing; diarrhea; problems with urination; or changes to taste.

When heart muscle is exposed to radiation therapy, as happens in treatment for breast cancer, Hodgkin lymphoma and cancers of the lung or esophagus, injuries can occur. These can include the heart valve injury that your relative experienced, as well damage to the coronary arteries, the tissues that cover the heart, the specialized cells that control heart rhythm and the heart muscle itself. These injuries can develop in the days and months after treatment, but are most often seen a year or more later.

The good news is that advances in radiotherapy over the years have lessened the incidence of cardiac injury. In addition, modern treatment protocols are often performed in partnership with a cardiologist. Their job is to assess a patient’s risk of heart injury prior to treatment and to monitor their progress during the course of radiotherapy. The goal is to craft an effective cancer treatment that doesn’t cause more health problems than it solves.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.

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