Understanding Radiation Therapy

Approved by the Cancer.Net Editorial Board, 08/2020

Radiation therapy is the use of high-energy x-rays 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.

What are the goals of radiation therapy?

Radiation oncologists use radiation therapy to destroy cancer cells and slow tumor growth while limiting the harm to nearby healthy tissue.

Sometimes, doctors recommend radiation therapy as the first cancer treatment. Other times, people receive radiation therapy after surgery or therapies using medication, like chemotherapy. This is called adjuvant therapy. It targets cancer cells remaining after the initial treatment.

When it is not possible to destroy all the cancer, doctors may use radiation therapy to shrink tumors and relieve symptoms. This is called palliative radiation therapy. Palliative radiation therapy may reduce pressure, pain, and other symptoms. The goal is to improve a person’s quality of life.

More than half of people with cancer receive some type of radiation therapy. For some cancers, radiation therapy alone is an effective treatment. Other types of cancer respond best to combination treatments, which is using more than 1 treatment for a patient's treatment plan. For instance, this may include radiation therapy plus surgery, chemotherapy, or immunotherapy.

What is external-beam radiation therapy?

External-beam radiation therapy is the most common type of radiation therapy. It delivers radiation from a machine outside the body. It can 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 near the cancer cells.

Most treatments are given every weekday for several weeks. Form-fitting supports or plastic mesh masks are used for radiation therapy to the head, neck, or brain to help people stay still during treatment.

The types of external-beam radiation therapy are:

Three-dimensional conformal radiation therapy (3D-CRT). Detailed 3-dimensional pictures of the cancer are created, typically from computed tomography (CT) or magnetic resonance imaging (MRI) scans. This allows the treatment team to aim the radiation therapy more precisely. It often means that they can safely use higher doses of radiation therapy while reducing damage to healthy tissue. This lowers the risk of side effects. For instance, dry mouth is common after radiation therapy for head and neck cancer. But 3D-CRT can limit the damage to the salivary glands that causes dry mouth.

Intensity modulated radiation therapy (IMRT). This is a more complex form of radiation. With IMRT, the intensity of the radiation is varied within each field unlike conventional 3D-CRT, which uses the same intensity throughout 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 the specific dose of radiation therapy. Unlike with x-ray beams, there is very little radiation dose beyond the tumor. This limits damage to nearby healthy tissue. Currently, doctors use proton therapy to treat certain types of cancer. This therapy is relatively new and requires special equipment. Therefore, it is not available at every medical center. Learn more about proton therapy.

Image-guided radiation therapy (IGRT). This refers to the practice of using daily images of each treatment field to confirm patient positioning and make sure the target is in the field. These daily images are compared to the images used to plan treatment. IGRT allows your doctor to make each treatment field smaller. This allows better targeting of the tumor and helps reduce damage to healthy tissue.

Stereotactic radiation therapy (SRT). This treatment delivers a large, precise radiation therapy dose to a small tumor area. The patient must remain very still. Head frames or individual body molds help limit movement. SRT is often given as a single treatment or in fewer than 10 treatments. Some patients 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 and may require a hospital stay.

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. But some radiation may exit the patient’s body. This requires safety measures to protect others from radiation exposure. Over time, the implants lose radioactivity. And the inactive seeds remain in the body.

Temporary internal radiation therapy. This is when radiation therapy is given in one of these ways:

  • Needles

  • Tubes, called catheters, that carry fluid in or out of the body

  • Special applicators

The radiation stays in the body for anywhere from a few minutes to a few days. Most people receive radiation therapy for just a few minutes. Sometimes, people receive internal radiation therapy for more time. If so, they stay in a private room to limit other people's exposure to the radiation.

What are other radiation therapy options?

Intraoperative radiation therapy (IORT). This treatment delivers radiation therapy to the tumor during surgery using either external-beam or internal radiation therapy. IORT allows surgeons to move away healthy tissue in advance. 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 saliva, sweat, and urine. These fluids are radioactive and people in close contact with the patient should take the safety measures recommended by the health care team. An example of this is radioactive iodine therapy (RAI; I-131) for thyroid cancer.

Radioimmunotherapy. This is a type of systemic therapy. 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 surrounding normal tissue. An example is ibritumomab (Zevalin), which is used in the treatment of some lymphomas.

Radiosensitizers and radioprotectors. Researchers are studying radiosensitizers. These 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.

Having radiation therapy slightly increases the risk of developing a second cancer. 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 become radioactive. And the radiation remains in the treatment room.

However, internal radiation therapy causes the patient to give off radiation. As a result, visitors should follow these safety measures:

  • 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 close or more than 5 minutes of contact with children or pregnant women.

Similarly, people who have had systemic radiation therapy should use safety precautions. For the first few days after treatment, take these safety measures:

  • 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 contact.

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

Questions to ask the health care team

  • 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 it?

  • Will I need to get a mesh mask or support made before my treatment begins?

  • Where will I receive radiation therapy?

  • What side effects can I expect during radiation therapy? Afterwards?

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

  • 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.