What is Radiation Therapy?

Approved by the Cancer.Net Editorial Board, 05/2022

Radiation therapy is a cancer treatment that uses high-energy x-ray or other particles to destroy cancer cells. A doctor who specializes in giving radiation therapy to treat cancer is called a radiation oncologist. A radiation therapy regimen, or schedule, usually consists of a specific number of treatments given over a set period.

Radiation therapy can treat many different types of cancer. It can also be used in combination with other cancer treatments, such as chemotherapy and/or surgery.

This article provides a general overview of radiation therapy, the different types of radiation therapy, and why it is used to treat cancer. Learn more about what to expect when having radiation therapy and the side effects of radiation therapy.

How does radiation therapy treat cancer?

Cancer begins when healthy cells change and grow out of control. All cells in the body go through a cycle to grow, divide, and multiply. Cancer cells go through this process faster than normal cells. Radiation therapy damages cell DNA so the cells stop growing or are destroyed.

Unlike other cancer treatments affect the whole body, such as chemotherapy, radiation therapy is usually a local treatment. This means it generally affects only the part of the body where the cancer is located. Some healthy tissue near the cancer cells may be damaged during the treatment, but it usually heals after treatment ends.

There are many different types of radiation therapy, and they all work a little bit differently to destroy cancer cells.

What are the goals of radiation therapy?

The goals of radiation therapy depend on your type of cancer and if and how far it has spread. Radiation therapy can be given alone or as a part of a treatment plan that includes different treatments. Some of the ways radiation therapy is used include:

As the primary treatment. Often, the goal of radiation therapy is to get rid of all the cancer and keep it from coming back.

Before other treatments. Radiation therapy can be given before other treatments, such as surgery, to shrink a large tumor. This is called "neoadjuvant radiation therapy."

After other treatments. Radiation therapy can be given after other kinds of treatments to destroy any remaining cancer cells. This is called "adjuvant radiation therapy."

To relieve symptoms. Radiation therapy can be used to relieve the signs and symptoms of cancer. This is called "palliative radiation therapy."

Radiation therapy can be used to treat many different types of cancer. More than half of people with cancer will receive some type of radiation therapy. For some cancers, radiation therapy alone is an effective treatment. Other types of cancer respond best to a combination of treatments. Radiation therapy can also be used to treat recurrent cancer and metastatic cancer. Recurrent cancer is cancer that comes back after treatment. Metastatic cancer is cancer that has spread to other parts of the body.

What are the types of external-beam radiation therapy?

The most common type of radiation therapy is external-beam radiation therapy. It delivers radiation from a machine outside the body. It can be used to treat large areas of the body, if needed.

A machine called a linear accelerator, or linac, creates the radiation beam for x-ray or photon radiation therapy. Special computer software adjusts the beam's size and shape. This helps target the tumor while avoiding healthy tissue nearby.

Most radiation therapy treatments are given every weekday for several weeks. Form-fitting supports or a plastic mesh mask are used for radiation therapy to the head, neck, or brain to help people stay still and make sure the beam reaches the same area each session.

The different types of external-beam radiation therapy are:

  • Three-dimensional conformal radiation therapy (3D-CRT). During this type of radiation therapy, detailed 3-dimensional pictures of the cancer are created from computed tomography (CT) or magnetic resonance imaging (MRI) scans. The treatment team uses these images to aim the beam. With this technique, the treatment team can safely use higher doses of radiation therapy and reduce damage to healthy tissue. This lowers the risk of side effects.

  • Intensity modulated radiation therapy (IMRT). This is a more complex form of radiation therapy. With IMRT, the intensity of the radiation is varied. This is different than conventional 3D-CRT, which uses the same intensity with each beam. IMRT targets the tumor and avoids healthy tissue better than conventional 3D-CRT.

  • Proton beam therapy. This treatment uses protons rather than x-rays. A proton is a positively charged particle. At high energy, protons can destroy cancer cells. The protons go to the targeted tumor and deposit a specific dose of radiation therapy. Unlike x-ray beams, very little radiation dose goes beyond the tumor with proton therapy. This limits damage to nearby tissue. Proton therapy is a relatively new treatment that requires special equipment. It is currently only used to treat certain types of cancer. Learn more about proton therapy.

  • Image-guided radiation therapy (IGRT). IGRT uses imaging during radiation treatment. Images are taken right before and during treatment and compared to imaging taken before treatment began. This helps doctors position the radiation as precisely as possible.

  • Stereotactic radiation therapy (SRT). This treatment delivers a large, precise dose to a small tumor area. The patient must remain very still. A head frame or individual body molds help limit movement. SRT is often given as a single treatment or in fewer than 10 treatments. Some people may need more than one course of SRT.

What is internal radiation therapy?

Internal radiation therapy is also called brachytherapy. This type of radiation therapy is when radioactive material is placed into the cancer or surrounding tissue. Implants may be permanent or temporary. This treatment may require a hospital stay.

The different types of internal radiation therapy include:

  • Permanent implants. These are tiny steel seeds that contain radioactive material. The capsules are about the size of a grain of rice. They deliver most of the radiation therapy around the implant area. However, some radiation may exit the patient's body. This requires safety measures to protect others from radiation exposure. Over time, the implants lose radioactivity. The inactive seeds remain the body.

  • Temporary internal radiation therapy. This type of radiation therapy can be given by needle, through a tube called a catheter, and through special applicators. The radiation stays in the body for anywhere from a few minutes to a few days. Most people receive internal radiation therapy for just a few minutes. Sometimes, internal radiation therapy can be given for more time. If so, they stay in a private room to limit other people's exposure to radiation.

What are the other radiation therapy treatment options?

Other radiation therapy treatment options include:

  • Intraoperative radiation therapy (IORT). This treatment delivers radiation therapy to the tumor during surgery using either external-beam or internal-beam radiation therapy. IORT allows surgeons to move healthy tissue out of the way so that it does not get damaged during the radiation therapy. This treatment is useful when vital organs are close to the tumor.

  • Systemic radiation therapy. Patients swallow or receive an injection of radioactive material that targets cancer cells. The radioactive material leaves the body through urine, saliva, and sweat. These fluids are radioactive, and people in close contact with the patient should take the safety measures recommended by the health care team (see below). An example of systemic radiation therapy is radioactive iodine therapy (RAI; I-131) for thyroid cancer.

  • Radioimmunotherapy. This is a type of systemic therapy. Specifically, it uses monoclonal antibodies, which are proteins that are attracted to very specific markers on the outside of cancer cells, to deliver radiation directly to the tumors. Because the treatment uses these special antibodies, there is less effect on the surrounding normal tissue. An example is ibritumomab (Zevalin), which is used in the treatment of some lymphomas.

  • Radiosensitizers and radioprotectors. Researchers are studying radiosensitizers and radioprotectors. Radiosensitizers are substances that help radiation therapy better destroy tumors. Radioprotectors are substances that protect healthy tissues near the treatment area. Examples of radiosensitizers include fluorouracil (5-FU, Adrucil) and cisplatin (Platinol). Amifostine (Ethyol) is an example of a radioprotector.

Is radiation therapy safe for patients and their families?

Doctors have safely and effectively used radiation therapy to treat cancer for more than 100 years.

Like other cancer treatments, radiation therapy causes side effects. Talk with your health care team about what to expect and what you are experiencing during and after your treatment. While most people feel no pain when each treatment is being delivered, effects of treatment slowly build up over time and may include discomfort, skin changes, or other side effects, depending on where in the body treatment is being delivered.

Having radiation therapy slightly increases the risk of developing a second cancer later in life. But for many people, radiation therapy eliminates the existing cancer. This benefit is greater than the small risk that the treatment could cause a new cancer in the future.

During external-beam radiation therapy, the patient does not give off any radiation after treatment sessions. Any radiation remains in the the treatment room.

However, internal radiation therapy causes the patient to give off radiation. As a result, visitors should follow these safety measures, unless other directions are given by the patient's doctor:

  • Do not visit the patient if you are pregnant or younger than 18

  • Stay at least 6 feet from the patient's bed

  • Limit your stay to 30 minutes or less each day

Permanent implants remain radioactive after the patient leaves the hospital. Because of this, for 2 months, the patient should not have more than 5 minutes of contact with children or pregnant people.

Similarly, people who are treated with systemic radiation therapy should follow safety precautions. Here are some common safety measures for the first few days after treatment. Be sure to talk with your health care team about specific instructions about your treatment.

  • Wash your hands thoroughly after using the toilet

  • Use separate utensils and towels

  • Drink plenty of fluids to flush the remaining radioactive material from the body

  • Avoid sexual activity

  • Try to avoid contact with infants, children, and pregnant people

Questions to ask the health care team

Consider asking your health care team these questions if radiation therapy is recommended as part of your cancer treatment plan:

  • What type of radiation therapy is recommended for me? Why?

  • What is the goal of having radiation therapy? Is it to eliminate the cancer, help me feel better, or both?

  • How long will it take to have this treatment? How often will I have radiation therapy?

  • Will I need to get a mesh mask or support made before my treatment begins? Can you describe this process?

  • Where will I receive radiation therapy?

  • What short-term side effects can I expect during radiation therapy?

  • What can be done to relieve side effects I experience?

  • Who should I talk with about any side effects I experience? How soon?

  • How will this treatment affect my daily life? Will I be able to work, exercise, and perform my usual activities?

  • What are the possible long-term side effects of this type of radiation therapy?

  • Whom should I call with questions or problems?

  • How can I reach them during regular office hours? After hours?

  • If I'm very worried or anxious about having this treatment, what can I talk with?

  • If I'm worried about managing the cost of this treatment, who can help me?

  • Will special precautions be needed to protect my family and others from radiation therapy I receive?

  • Will I receive other cancer treatments in addition to radiation therapy?

  • When will we know if this treatment was successful? How?

Related Resources

What to Expect When Having Radiation Therapy

Side Effects of Radiation Therapy

Making Decisions About Cancer Treatment

More Information

National Cancer Institute (NCI): Brachytherapy to Treat Cancer

NCI: External Beam Radiation Therapy for Cancer

RadiologyInfo.org: Introduction to Cancer Therapy (Radiation Oncology)

RTAnswers.org: How Does Radiation Therapy Work

ASCO answers; Radiation TherapyDownload ASCO's free Radiation Therapy fact sheet. This 1-page printable PDF gives an introduction to radiation therapy, including an overview of the different types of radiation, what to expect during treatment, possible side effects, terms to know, and questions to ask the health care team. Order printed copies of this fact sheet from the ASCO Store.