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What is radiation therapy?

Updated: Sep 14, 2020

More than half of all people with cancer receive radiation therapy as part of their cancer treatment. Doctors use radiation therapy to treat almost any type of cancer.

The term "radiation therapy" often refers to external beam radiation therapy. During this type of radiation, high-energy rays come from a machine that targets rays outside of your body at a precise point on your body. During a different radiation therapy called brachytherapy (brak-e-THER-uh-pee), the radiation is placed inside your body.

Radiation therapy damages cells by destroying the genetic material that controls how cells grow and divide. While both healthy and cancerous cells are damaged by radiation therapy, the goal of radiation therapy is to destroy as few healthy cells as possible. Normal cells can repair most of the damage caused by radiation.

How is radiation therapy used in people with cancer?

Your doctor may recommend radiation therapy as an option at different times during your cancer treatment and for different reasons, including:

  • As the sole (primary) treatment for cancer

  • Before surgery, to shrink a cancerous tumor (neoadjuvant therapy)

  • After surgery, to stop the growth of remaining cancer cells (adjuvant therapy)

  • In combination with other treatments, such as chemotherapy, to destroy cancer cells

  • To alleviate symptoms caused by cancer in advanced cancer

Radiation therapy can also help treat symptoms when cancer spreads. At this point, radiation is part of palliative care aimed at relieving a person's symptoms and improving their quality of life. It can also extend a person's life in some cases.

Palliative radiation therapy usually involves lower doses and fewer treatment sessions than curative therapy. For example, in some people with bone cancer, palliative radiation therapy can help prevent the development of painful tumors.

Types of radiation therapy

There are two types of radiation therapy. These:


This is the most common type. It contains an external machine that emits a beam of radiation that targets the treatment area. Different forms are available depending on the need. For example, high-energy rays can target cancer deeper in the body.


There are different types of internal radiation therapy. Both involve implanting or introducing a radioactive material into the body.

Brachytherapy involves placing a radioactive implant in or near cancerous tissue. Implant can be temporary or permanent. Another type of internal radiation therapy involves receiving an injection of radioactive fluid. The aim is to limit the exposure of healthy tissue around the cancer to radiation. Doctors may recommend this treatment for prostate or ovarian cancer, for example.

Your doctor may recommend both main types of radiation therapy based on the type of cancer or the condition of the disease. The decision as to which treatment to take will depend on:

  • Cancer type

  • The size of the tumor

  • The location of the tumor, including nearby tissue types

  • The person's age and general health

How do you prepare?

Before starting external beam radiation therapy, your healthcare team guides you through the planning process to ensure that the radiation reaches the required sensitive point in your body. Planning typically includes:

Radiation simulation: During the simulation, your radiation therapy team works with you to find a comfortable position for you. You must lie down during treatment. Therefore, finding a comfortable position is vital. To do this, you lie down on a special table with the one used during radiation therapy. Cushions and restraints are used to position you correctly and help keep you still. Your radiation therapy team will mark the area where your body will be exposed to radiation. Depending on your situation, you can make temporary markings with a marker or use small temporary tattoos.

Scan planning: Your radiation therapy team will have you have computed tomography (CT) scans to determine the area of ​​your body to be treated. After the planning process, your radiation therapy team decides what type of radiation and in what doses you will receive based on your cancer type and stage, your overall health, and the goals of your treatment.

The precise dose and focus of the radiation beams used in your treatment have been carefully planned to maximize radiation to your cancer cells and minimize damage to surrounding healthy tissue.

What are the expectations from radiation therapy?

External beam radiation therapy is usually performed using a linear accelerator, a machine that directs high-energy radiation beams into your body.

As you lie on a table, the linear accelerator moves around you to deliver radiation from several angles. The linear accelerator can be adjusted to your specific situation to give the exact radiation dose your doctor has detected.

You will usually receive outpatient external beam radiation five days a week over a period of time. In most cases, treatments are usually spread out over several weeks to allow healthy cells to heal between radiation therapy sessions.

Each treatment session is expected to take approximately 10 to 30 minutes. In some cases, a single treatment may be used to relieve pain or other symptoms associated with more advanced cancers.

During a treatment session, you lie down in the position determined for the radiation simulation session. Molded systems are used to keep you in place.

The linear accelerator machine can rotate around your body to reach the target from different directions. The machine buzzes.

During the treatment, which takes only a few minutes, you stop and breathe normally. For some patients with lung or breast cancer, you may be asked to hold your breath while the machine is performing the treatment.

Your radiation therapy team is in a room with video and audio connections so you can talk to each other. You should speak up if you are uncomfortable, but you will not feel any pain during your radiation therapy session.

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