The short answer
External beam radiation comes from a machine outside the body that aims radiation at the cancer. Internal radiation, called brachytherapy, places a radiation source inside the body, in or near the tumor. Both are local treatments that treat a specific area. A key difference is that external beam does not make you radioactive, while brachytherapy makes you give off radiation for a time.
External beam radiation comes from a machine that aims radiation at your cancer from outside the body.
Internal radiation (brachytherapy) places a radiation source inside your body, in or near the tumor.
Both are local treatments — they treat a specific part of the body, not the whole body.
External beam radiation does not make you radioactive; you can safely be around others.
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The full explanation.
The short version
Radiation therapy can be given in two main ways. The difference is where the radiation comes from:
- External beam radiation comes from a machine outside the body that aims radiation at your cancer.
- Internal radiation, called brachytherapy, places a radiation source inside your body, in or near the tumor.
Both are local treatments. They treat a specific part of the body, not the whole body.
How external beam radiation works
External beam radiation comes from a machine that aims radiation at your cancer. It treats a specific area. If you have cancer in your lung, for example, you will have radiation only to your chest, not your whole body. It is used for many types of cancer. Most people have it as an outpatient, usually once a day, five days a week, Monday through Friday, for a set number of weeks. You lie or sit very still. Each session's radiation lasts only about one to five minutes. You cannot feel, hear, see, or smell it.
How internal radiation (brachytherapy) works
Brachytherapy places seeds, ribbons, or capsules inside your body, in or near the tumor. Each one holds a radiation source. It is also a local treatment, so it treats only a specific part of your body. It is often used for cancers of the head and neck, breast, cervix, prostate, and eye. The source usually goes in through a small tube called a catheter, or through a larger device called an applicator.
Types of brachytherapy
Internal radiation comes in a few forms:
- Low-dose rate implants stay in place for 1 to 7 days, often during a hospital stay.
- High-dose rate implants are placed for just 10 to 20 minutes at a time. That may happen at daily or weekly outpatient visits.
- Permanent implants stay in the body for the rest of your life. The radiation gets weaker each day until almost all of it is gone.
The big difference: radiation and safety
This is where the two really differ. External beam radiation will not make you radioactive. You may safely be around other people, including pregnant women, babies, and young children.
Brachytherapy is different. While the source is in your body, it gives off radiation for a while. If the dose is high, you may need to follow safety steps. Those can include staying in a private room and limiting close time with others, above all children and pregnant women. Once a temporary source and its catheter come out, no radiation is left in your body, and it is safe for people to be near you.
The bottom line
External radiation is aimed from a machine outside the body. Internal radiation is placed inside, near the tumor. Both treat a specific area. Only brachytherapy makes you give off radiation for a time. Ask your care team which type is planned for you, what safety steps may be needed, how many treatments to expect, and how to care for yourself.
Words to know
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Common questions
What is the difference between external and internal radiation?
External beam radiation comes from a machine that aims radiation at your cancer from outside the body. Internal radiation, called brachytherapy, places a radiation source — such as seeds, ribbons, or capsules — inside your body, in or near the tumor. Both are local treatments.
Will radiation make me radioactive?
It depends on the type. External beam radiation therapy will not make you radioactive, and you may safely be around others, even young children and pregnant women. With brachytherapy, the source inside your body gives off radiation for a while, so you may need to follow some safety measures.
Is internal radiation always an overnight stay?
Not always. Brachytherapy comes in different types. Some low-dose implants stay in place for days, often in the hospital. High-dose implants may be placed for just minutes at a time during outpatient visits. Permanent implants stay in the body, getting weaker over time. Your care team explains which type fits you.
How do I know which type I will have?
The choice depends on your type of cancer and where it is. Brachytherapy is often used for cancers of the head and neck, breast, cervix, prostate, and eye. Before treatment, you meet with your doctor or nurse to plan it and discuss benefits and side effects, and you decide whether to proceed.
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Last updated: 2026-08-10Next planned review: 2027-01-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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