Radiation therapy can affect any part of the heart. Different forms of radiation cardiotoxicity result, depending on which area was damaged. This section covers the most common types of radiation cardiotoxicity.

Pericarditis and Pericardial Effusion

Radiation therapy to the heart can cause irritation and inflammation of the pericardium, a fluid-filled space surrounding the heart. Such inflammation, known as pericarditis, can occur at any time after the start of radiation, from immediately to months or years after treatment. Symptoms of pericarditis include shortness of breath and chest pain that may be eased by leaning forward. If the inflammation is significant, it can also spread to the heart muscle, and is termed “myopericarditis.”

Radiation therapy can cause pericardial effusion, or the development of a fluid collection in the pericardial sac. Such fluid buildup can cause shortness of breath, chest pressure and lightheadedness. It may need to be removed.

Cardiomyopathy and Heart Failure

Radiation therapy can injure and scar the muscle cells of the heart. This scarring can cause the heart muscle to become weak or stiff. These conditions are known as cardiomyopathies. Weakening or stiffening of the heart muscle can make it difficult for the heart to pump enough blood to meet the body’s needs, a condition called heart failure. One of the main symptoms is fluid buildup in the body, especially the lungs and legs. Cardiomyopathy and heart failure from radiation therapy generally develop many years after treatment.

Coronary Artery Disease, Atherosclerosis and Heart Attack

The coronary arteries supply blood to the heart. Any disruption in this blood supply can interfere with the heart’s pumping function. Coronary arteries can become blocked or clogged with atherosclerosis or plaque. A significant blockage or sudden blockage in the coronary arteries can be very serious. This can lead to severe damage or death of heart tissue and is known as a heart attack (also called myocardial infarction). Common symptoms of a heart attack include shortness of breath, and chest pain or pressure that can come and go or be constant. These symptoms can be observed during or made worse by exertion. Less common symptoms are sweating, nausea, weakness, lightheadedness, and fatigue. If you think you are having a heart attack, dial 911 at once.

Radiation therapy in the area of the heart can injure the coronary arteries. This injury can speed up atherosclerosis and increase the risk of a heart attack. Coronary artery disease caused by radiation therapy generally develops many years after treatment. However, with radiation, the development of heart disease occurs earlier than normal. As a result, patients who receive radiation therapy in the area of the heart can develop coronary artery disease at younger ages than normally expected. So it is important for these individuals to be screened for heart disease. Your doctor may recommend stress testing to assess your heart.

Heart Valve Disease

The heart contains four valves that help blood move through the heart normally. They open to let blood flow forward and close to prevent blood from flowing backward. Radiation therapy can cause thickening, fibrosis, and calcium buildup of the valves. This prevents the valves from fully closing, leading to backward flow (regurgitation). This can also cause thickening and narrowing of the valves, which prevents opening and limits forward flow (stenosis). Both regurgitation and stenosis can occur many years after radiation therapy. Common signs are shortness of breath (worse with exertion), swelling in the ankles, fatigue, weakness, chest pressure, and lightheadedness.

Heart Rhythm Problems (Arrhythmias)

Normal heart function relies on a series of coordinated electrical events inside the heart that occur at the right time and in the right order. This rhythm repeats tens to hundreds of thousands of times throughout the day and is controlled by the heart’s electrical wiring system (conduction system). Radiation therapy can damage the conduction system and disturb the rhythm of the heart.

Any disturbance in the heart’s rhythm is called an arrhythmia. With some arrhythmias, heart rhythm is abnormally fast, and with others, the rhythm is too slow. Arrhythmias caused by radiation therapy are not common. However, when they do develop, they can be slow arrhythmias and occur months to years after treatment. Early on, they may be fast rhythms (for example atrial fibrillation, supraventricular tachycardia).

Radiation Risks

Many factors influence the risk of radiation causing heart problems or making them worse. Your doctor will consider your individual case and work with you to select the most effective treatment for limiting your risk of developing heart problems. Here we will explore many of these considerations in radiation treatment.

Total Radiation Dose:

Depending on the type of cancer you have, your doctor will use a specific total dose or amount of radiation to treat your cancer. Over time, many studies have been conducted to identify the most effective, yet safest dose, to cure or control your cancer. In some cases, data received from such studies have resulted in a decreased radiation dose compared to what has been considered standard care in the past.

For example, studies of Hodgkin’s lymphoma have led to using patient characteristics to determine the lowest dose of radiation that will control lymphoma. The dose of radiation is measured in units of Gray (Gy). As an example, in patients with favorable Hodgkin’s lymphoma, some patients may receive a dose as low as 20 Gy as compared to higher risk patients, who may require a radiation dose of 30-45 Gy to treat their lymphomas.

Radiation Fields:

Radiation oncologists attempt to limit the area of tissue treated with radiation (called the radiation field) without decreasing needed treatment of the cancer. The risk of developing heart toxicities after radiation is associated with the amount and areas of the heart within the radiation field. Even if the heart is not targeted in your treatment, there may be some overlap of radiation to the heart depending on where your cancer is located.

Types of radiation fields:

Extended field radiation therapy (EFRT): With Hodgkin’s lymphoma as an example, in the past, patients were treated with larger radiation fields called “extended field radiation therapy,” which included both the cancerous lymph nodes as well as healthy lymph nodes in the region. Typically, this included lymph nodes in an area near the heart called the mediastinum.
Involved field radiation therapy (IFRT): However, with improvements in chemotherapy and radiation, studies have shown that the field can be smaller and the radiation aimed only to the region of cancerous lymph nodes. This is called “involved field radiation therapy.”
Involved site radiation therapy (ISRT): Even more recently, the concept of “involved site radiation therapy,” has been used. ISRT treats the cancerous regions and typically treats a smaller field than what would be treated with IFRT.

Your radiation oncologist will help determine what area needs to be treated by taking into consideration many factors, including a physical exam, diagnostic imaging, and a thorough medical history. The oncologist will also confirm whether chemotherapy and/or certain targeted agents being used in your treatment and, if so, your response to these therapies. Although your doctor will attempt to reduce the radiation dose to your heart, the main concern is to control the cancer.

Another disease in which radiation fields may increase the dose to your heart is breast cancer, specifically when it is on the left side. Because the heart lies just behind the left breast, there is a risk of higher radiation dose to the heart when treating this area. Radiation oncologists work to treat patients effectively for their cancers but limit the dose to the heart.

Some patients need to receive radiation to lymph nodes by the breast bone (sternum). However, there are ways that a radiation oncologist can attempt to decrease the dose to this area. Again, although it is important to limit the dose of radiation the heart receives, your doctor will not want to compromise the chance of curing your cancer.

Age :

Studies have shown that receiving radiation at a younger age is associated with a greater risk of developing heart disease later in life. As treatment of cancer improves, we are, thankfully, seeing more patients survive their cancer and live many years after treatment. Since radiation effects on the heart can occur years after cancer treatment has ended, it is especially important that young cancer patients follow up regularly with doctors throughout their lives.

Radiation Techniques :

Another way to limit the dose of radiation to the heart is through how the radiation is delivered.

3D-conformal radiation (3DCRT) is a delivery method that shapes the radiation dose around normal or healthy tissues in your body. This is done by taking a CT of your body in the position in which you will receive treatment. With this CT scan, the radiation oncologist and dosimetrist (a person trained in developing radiation plans using computer software systems) work to design a plan that avoids healthy tissue and targets the cancerous tissue. The treatment is delivered from a few angles. They are all focused directly at the cancer, and thus the highest dose of radiation combines from these different angles to increase the dose to the cancer and limit the dose to healthy tissue.
Intensity-modulated radiotherapy (IMRT) is similar to 3DCRT in that it is used to deliver the highest dose of radiation to the tumor and decrease the radiation to surrounding healthy tissue. This is done by using small pieces of metal that move in and out to shape the radiation around the tumor itself. However, it is important to know that this technique is not always more effective than 3DCRT. Your radiation oncologist can discuss which treatment techniques are best for your individual case.
Image-guided radiotherapy (IGRT) is another sophisticated development in radiation treatment. This technique uses special daily imaging to make small adjustments at the time of treatment. Pictures similar to an X-ray of a bone or a small CT scan are taken that allow the radiation therapists and physicians to make adjustments to precisely set you up for treatment. This helps deliver radiation to the target and helps decrease the dose to surrounding areas.
Your position for radiation treatment can also help limit how much radiation is received by the heart. For example, being treated on your stomach can shift the breast away from your heart and reduce your risk of hurting the heart.

Another way to limit the dose of radiation to the heart is through how the radiation is delivered.

3D-conformal radiation (3DCRT) is a delivery method that shapes the radiation dose around normal or healthy tissues in your body. This is done by taking a CT of your body in the position in which you will receive treatment. With this CT scan, the radiation oncologist and dosimetrist (a person trained in developing radiation plans using computer software systems) work to design a plan that avoids healthy tissue and targets the cancerous tissue. The treatment is delivered from a few angles. They are all focused directly at the cancer, and thus the highest dose of radiation combines from these different angles to increase the dose to the cancer and limit the dose to healthy tissue.
Intensity-modulated radiotherapy (IMRT) is similar to 3DCRT in that it is used to deliver the highest dose of radiation to the tumor and decrease the radiation to surrounding healthy tissue. This is done by using small pieces of metal that move in and out to shape the radiation around the tumor itself. However, it is important to know that this technique is not always more effective than 3DCRT. Your radiation oncologist can discuss which treatment techniques are best for your individual case.
Image-guided radiotherapy (IGRT) is another sophisticated development in radiation treatment. This technique uses special daily imaging to make small adjustments at the time of treatment. Pictures similar to an X-ray of a bone or a small CT scan are taken that allow the radiation therapists and physicians to make adjustments to precisely set you up for treatment. This helps deliver radiation to the target and helps decrease the dose to surrounding areas.
Your position for radiation treatment can also help limit how much radiation is received by the heart. For example, being treated on your stomach can shift the breast away from your heart and reduce your risk of hurting the heart.

3D treatment planning:

In addition to using 3DCRT to plan your treatment, you may read about or hear your doctor refer to a “dose-volume histogram” (DVH). The dose volume histogram is a computer tool that can be used to determine the dose an organ, such as your heart, will receive. Different studies have published constraints, or limits, that can be used to help determine the risk of heart problems based on the dose the heart receives. By using these techniques, the dose to the heart can be decreased significantly.

Motion Management:

Another way of reducing the radiation dose to normal tissue is the use of tools to decrease motion of organs when breathing in and out. For example, if a person has lung cancer, the tumor in the lung will move up and down when the person inhales and exhales. A belt can be applied over the patient’s midsection to help the patient decrease big breaths that result in greater motion. A special type of CT scan is done that can watch the tumor’s movement and account for this breathing in treatment planning. Another technique includes a process called “gating.” This treats only the tumor during certain times in the patient’s breathing cycle. All of these efforts attempt to decrease the amount of radiation to normal tissue.

Another method of limiting radiation cardiotoxicity is called “deep inspiration breath-hold” (DIBH). This can be used for women with left-sided breast cancer to reduce the radiation dose to the heart. Patients are instructed to take a deep breath and hold the breath while they are treated with radiation. This expands the lungs with air and puts a greater distance between the heart and chest wall (the ribs and muscles just under the breast). By increasing the distance from the chest wall, the dose of radiation to the heart decreases. This can also be used in the treatment of certain lung cancer patients.

Radiation Type:

Another factor that affects the radiation dose to the heart is what type of radiation is used. There are several radiation types you may have heard about including the most common form, known as “photon” radiation, which uses X-rays to treat your cancer. Additional forms of radiation treatment for cancer may include “proton” or “electron” radiation These forms of radiation have different properties that can be used in an attempt to limit the dose of radiation to your heart.

Proton therapy is a type of radiation available in only a limited number of centers. Using this therapy, radiation to normal tissues can be reduced. However, there is no current clinical data that shows proton therapy reduces cardiotoxicity.

Chemotherapy history:

Certain types of chemotherapy affect the heart, including the class of medicines called “anthracyclines” (i.e. daunorubicin, doxorubicin, epirubicin, and idarubicin) and anthracycline-like medicines (i.e. mitoxantrone). When combined with radiation that may involve the heart, there is an increased potential for heart damage, heart failure and side effects.