Radiation therapy

Radiation therapy uses focused high-energy beams to damage cancer cells in one part of the body.

Rosa: Hi, I'm Rosa. Radiation treats cancer in one part of the body with focused beams. Let me explain what a treatment day looks like and how to care for yourself.

Radiation therapy uses high-energy rays, like very strong x-rays, to kill cancer cells or stop them from growing. It treats only the area the beams are aimed at. About half of people with cancer get radiation at some point.

Radiation damages the DNA inside cells. Cancer cells are less able to repair this damage than normal cells, so they die over time. Normal cells in the treated area can be affected too, but they usually heal. The effect builds up over days to weeks, and keeps working after treatment ends.

The most common type is external beam radiation. A machine aims beams at the tumor from outside the body. It does not hurt, and you will not feel it. Each visit takes a few minutes of actual treatment. Courses vary widely: some last one day, some a week or two, and others are given on weekdays for several weeks. Before you start, you will have a planning session, called a simulation, with a scan and sometimes small skin marks or a custom mold to help you hold still.

Other types include brachytherapy, where a radiation source is placed inside or next to the tumor for a time, and stereotactic radiation, which gives very precise, high doses in just a few sessions. Radiation can be used to cure cancer, alongside surgery or chemo, or to ease pain and other symptoms.

Side effects mostly depend on the area treated. Tiredness and skin changes, like redness, dryness, or peeling, are common. Treating the head and neck can cause mouth sores, dry mouth, and taste changes. Treating the chest can cause trouble swallowing or cough. Treating the belly or pelvis can cause nausea, diarrhea, or bladder irritation. Most side effects start a couple of weeks in and fade within weeks after treatment ends. Some effects can show up months or years later, so ask about long-term risks.

Call your care team for skin that blisters, opens, or looks infected, pain that is not controlled, trouble swallowing or not being able to eat or drink, severe diarrhea, new shortness of breath or cough, or fever of 100.4°F (38°C) or higher if you are also getting chemo. If it feels very bad, call 911.

Am I radioactive?

With external beam radiation, you are not radioactive and it is safe to be around others, including children and pregnant people. With some internal radiation, you may need short-term precautions. Your team will explain.

Skin care

Wash the area gently with mild soap and lukewarm water. Use only lotions your team approves. Avoid sun, heat packs, and tight clothes on the treated skin.

Keep your schedule

Try not to miss sessions. Gaps can make treatment less effective. If you have trouble getting rides, ask a social worker for help.

Tiredness

Fatigue often builds during treatment. Light activity like walking, along with rest, can help. Ask for help with chores and rides.

Questions to ask

What is the goal of my radiation? How many sessions will I need? What side effects should I expect for the area being treated? Are there long-term effects I should know about?

Myth: Radiation makes you lose hair everywhere

Fact: Radiation causes hair loss only in the area being treated. Radiation to the chest, for example, does not cause hair loss on your head.

Myth: Radiation is only for advanced cancer

Fact: Radiation is often used to cure early cancers, sometimes as the main treatment. It is also used to relieve pain and other symptoms.

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.