Radiation Therapy
Radiation therapy is one of the most common treatments for cancer. You might also hear it called radiotherapy, irradiation, x-ray therapy, radiation treatment, or sometimes just radiation.
Learn more about how radiation therapy works, what to expect when you get radiation, and what questions to ask your cancer care team about your treatment.
What is radiation therapy?
Radiation therapy uses high-energy particles or waves, such as x-rays, gamma rays, electron beams, or protons, to destroy or damage cancer cells. It may be used alone or with other treatments, like surgery, chemotherapy (chemo), hormone therapy, or targeted therapy.
How is radiation therapy used to treat cancer?
The cells in your body grow and divide to form new cells. But cancer cells grow and divide faster than most normal cells.
Radiation for cancer works by making small breaks in the DNA inside cells. This keeps cancer cells from growing and dividing and causes them to die.
Nearby healthy cells can be damaged by radiation, but most healthy cells heal and go back to working the way they should.
How is radiation therapy given?
Radiation therapy can be given in 3 ways. Sometimes, more than one type of radiation is used.
The type of radiation therapy you get depends on your cancer and where it is in your body. Your cancer care team can answer specific questions about the type of radiation you’re getting, how it will affect your body, and any safety measures you need to take.
External radiation (also known as external beam radiation) uses a machine to direct high-energy rays from outside your body into the tumor. It’s done during outpatient visits to a hospital or treatment center.
External radiation is usually given daily (Monday–Friday) for many weeks. Sometimes, it’s given twice a day for several weeks. If you get external radiation, you are not radioactive and don’t have to follow special safety measures at home.
Internal radiation is also called brachytherapy. During this treatment, a radioactive source is put inside your body, either into or near the tumor.
- Sometimes, the radiation source is put in your body permanently.
- Sometimes, it is placed in your body for a certain amount of time and then removed.
This depends on your type of cancer.
If you get internal radiation, you do have to take special safety measures for a period of time. If the source is left in your body permanently, it eventually stops giving off radiation.
Systemic radiation uses radioactive drugs to treat certain types of cancer. These drugs are taken by mouth or put into a vein, and they travel throughout your body.
If you get systemic radiation, you might have to follow special safety measures at home for a period of time.
The type of radiation therapy you get depends on your cancer and where it is in your body. Sometimes, more than one type of radiation is used. Your cancer care team can answer specific questions about the type of radiation you’re getting, how it will affect your body, and any safety measures you need to take.
Learn more: What Goes Into Planning Your Radiation Therapy
When your cancer care team plans your radiation therapy, they look at many things, including your cancer type and stage, treatment goals, and overall health. This helps them decide the best type of radiation therapy for you.
What is the goal of radiation therapy?
Most types of radiation therapy don’t reach all parts of the body. This means they aren’t helpful in treating cancer that has spread to many places within the body. Still, radiation therapy can be used to treat many types of cancer, either alone or in combination with other treatments.
Each cancer and each person is different, but radiation is often the treatment of choice for the following goals:
- In cancers that are sensitive to radiation, it may be used alone to make the cancer shrink or completely go away.
- Radiation may be given at the same time as chemo or other types of anti-cancer medicines.
- Radiation may be used after chemo or other anti-cancer drugs are given.
- It may be used before surgery to shrink the tumor (pre-operative therapy or neoadjuvant therapy), OR
- After surgery to help keep the cancer from coming back (adjuvant therapy).
- Radiation is sometimes used to treat areas where a type of cancer most often spreads. The goal is to kill any cancer cells before they grow into tumors.
- For example, certain types of lung cancer often spread to the brain. A person with this type of cancer may get radiation to their brain, even when doctors haven’t found any cancer there. This is done to help prevent cancer from spreading to the head.
- Radiation to prevent future cancer may be given at the same time as radiation to treat existing cancer, especially if the area where the cancer might spread is close to the tumor itself.
- Radiation might help relieve problems caused by advanced cancer, like pain, trouble swallowing or breathing, or bowel blockages.
- This is called palliative radiation.
- If cancer returns (recurs), radiation might be used to treat it or to treat symptoms caused by advanced cancer. This depends on the location, the type of cancer, and the amount of radiation given to that part of the body in the past.
- Radiation might be used when cancer comes back in the same area of the body or when it comes back in a different area.
Who gets radiation therapy?
More than half of people with cancer get radiation therapy.
Sometimes, it is the only cancer treatment needed. Sometimes, it's used with other types of treatment. The decision to use radiation therapy will depend on the type and stage of your cancer and other health problems you might have.
How is radiation therapy different from other treatments?
Many treatments (like chemo) are taken by mouth or injected into a vein (IV). These usually expose your whole body to cancer-fighting medicines.
Unlike these treatments, radiation therapy is usually a local treatment. This means it’s aimed at the part of your body that needs treatment. Radiation therapy is carefully planned. The goal is to damage cancer cells with as little harm as possible to nearby healthy cells.
Some radiation treatments (systemic radiation therapy) do travel throughout your body.
These treatments use radioactive substances given in a vein or by mouth. Even though this type of radiation travels throughout your body, the radioactive substance mostly collects in the area of the tumor, so there is still little effect on the rest of the body.
What is it like to get radiation therapy?
Most people get radiation therapy at a cancer treatment center or hospital and go home the same day. But with some types of internal radiation treatment, you may need to stay at the hospital for 1–2 nights.
Each type of radiation therapy has its own routine, side effects, and safety steps. Learn what it’s like to get each type.
Side effects and safety
Learn more about radiation side effects, how long most side effects last, and what measures you might need to take to keep yourself and those around you safe.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: June 9, 2025
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