Radiation Risks

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 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.

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.

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.

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.

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.

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.

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.