What's the Difference Between Chemotherapy and Radiation?

Medically Reviewed by Laura J. Martin, MD on June 23, 2020

Chemotherapy and radiation therapy are both treatments for cancer – the uncontrolled growth and spread of cells to surrounding tissues.

Chemotherapy, or “chemo,” uses special drugs to shrink or kill cancer cells. Radiation therapy, or “radiation,” kills these cells with high-energy beams such as X-rays or protons.

Goals of Chemotherapy and Radiation

Both types of therapy share the same goals:

  • Cure: Get rid of all cancer cells and stop the cancer from coming back
  • Control: Shrink or slow cancer tumors or stop the spread of cancer cells to other parts of the body
  • Relief: Shrink tumors to lessen pain and other difficult symptoms of cancer (sometimes called palliative radiation therapy)

When a cure isn’t possible, both therapies can be powerful tools to slow the progress of your cancer and relieve pain and other uncomfortable symptoms.

How They Work

Though chemo and radiation both attack cancer cells, they work in different ways. Chemotherapy drugs circulate in your bloodstream. They kill or shrink cancer cells anywhere in your body, not just at the site where the first (primary) cancerous tumor starts. Because these drugs pass through your whole system, they’re called “systemic.”

Radiation treatment uses invisible bursts of energy instead of drugs. In addition, it is usually a “local” treatment that aims energy beams just at the area where cancer cells grow.

Which Therapy Do You Need

The type of cancer and what stage, or how far along, it is will help tell your doctor which therapy you need, or if you need both. In most cases, your doctor will want to approach treatment with a few different tools. These might include chemo and radiation, as well as surgery to remove tumors, targeted therapies, and other options.

You and your doctors may come up with a few different plans that could work. Don’t be afraid to ask questions about the pros and cons of different approaches.

How You Get Chemotherapy and Radiation

Both therapies typically happen over a period of weeks in regular visits to the hospital or doctor’s office. But each case is different, so talk to your doctor about the right treatment plan for you.

Your medical team will deliver your chemotherapy through one or more of these methods:

  • IV: Through a needle or a tube (port) directly into a blood vessel
  • Oral: From a pill or capsule that you swallow
  • Injection: Through a needle into the skin or muscle

Your medical team will deliver your radiation therapy through one or more of these methods:

  • External radiation: A machine outside the body shoots invisible high-energy beams into the tumor.
  • Internal radiation: This is sometimes called “brachytherapy.” Doctors place a radioactive object inside your body close to the tumor. They might leave it in to do its work or they may take it out soon afterward.
  • Systemic radiation: Though less common, your doctor might suggest using radiation as a systemic treatment that works throughout the body. That means you get it from a pill you swallow or through a needle or port into one of your veins.

Side Effects

Along with killing cancer cells, both chemo and radiation can damage healthy cells. This sometimes causes unpleasant side effects. The exact ones depend on the type and amount of treatment. They also depend on the person; some people have more serious side effects than others.

Some possible side effects that both share include:

Because radiation tends to focus on a particular area, you might notice more side effects in that spot. For example, treatment on your neck might make it hard for you to swallow. Radiation on your chest might cause you to cough or have shortness of breath. Because chemotherapy is systemic, it tends to cause more general symptoms.
Tell your medical team about any side effects that you notice. They can adjust your treatments or add medications to help you manage them where possible.

Show Sources


American Cancer Society: “Chemotherapy,” “Radiation Therapy.”

American Society of Clinical Oncology: “Understanding Chemotherapy,” “Making Decisions About Cancer Treatment.”

Cancer Research UK: “Chemotherapy.”

CDC: “Cancer Treatments.”

National Cancer Institute: “Types of Cancer Treatment,” “Radiation Therapy Side Effects.” “Side Effects of Chemotherapy and Radiation.”

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