Radiation therapy uses high-energy rays to damage cancer cells in one specific area of the body. This page explains the steps of treatment, modern techniques, and care during treatment in plain language.

What is radiation therapy?

Radiation therapy, also called radiotherapy, is cancer treatment with high-energy rays. These rays damage the DNA of cancer cells. Cancer cells cannot repair the damage well, so they gradually die or grow more slowly.

Radiation therapy is a local treatment. This means it targets only the area of the body where the cancer is. For example, in breast cancer the breast is treated, not the whole body.

Every patient’s treatment plan is different; ask your doctor about your own situation.

Who is it for?

Doctors suggest radiation therapy in these situations:

As the main treatment, sometimes together with chemotherapy
Before surgery, to shrink the tumor
After surgery, to destroy any cells left behind
To ease symptoms such as pain or pressure from a tumor

Whether radiation therapy is right for you depends on the type of cancer, where it is and its stage, and your general health. Your doctor and treatment team make this decision.

How is radiation therapy given?

External beam radiation and brachytherapy

In external beam radiation, a machine called a linear accelerator (linac), which is the radiation therapy machine, aims the beam at the tumor from outside the body. Most patients get this type.

In brachytherapy, also called internal radiation, a small radioactive source, such as a seed or capsule, is placed inside the tumor or close to it. It is used for some cancers, such as cervical, prostate, breast, and head and neck cancers. The source may stay for a few minutes up to a few days, or in special cases it is permanent. If brachytherapy is being considered for you, your doctor will explain the safety precautions during treatment, including those for visitors.

The steps of treatment

Visit and consultation. The doctor reviews your records, pathology reports, and imaging, and explains the goal of treatment and possible side effects.
Simulation (planning CT scan). A special CT scan is done in one session to find the exact treatment area. Marks may be made on your skin. For head and neck treatment, a custom mask is usually made so your head stays in the same position each day.
Treatment planning. A medical physicist and your doctor use software to plan the angles and dose of the radiation so the tumor gets the most and healthy tissue gets the least. This step can take a few days, and you do not need to be there.
Daily sessions. Most patients are treated as outpatients, usually on weekdays. The number of sessions ranges from one to several weeks of treatment.
Follow-up. During and after treatment, your doctor examines you and checks the results with tests or imaging.

Modern techniques

IMRT. The beam comes from many angles with different strengths, so its shape matches the shape of the tumor more closely.
VMAT. The machine rotates around you while giving the radiation in one continuous sweep. Sessions are usually shorter.
SBRT. For small, well-defined tumors, a high dose is given in a small number of sessions (up to about five). The aim is very precise.
Imaging during treatment (IGRT). Images are taken before the radiation to double-check your position.

These techniques are not available everywhere, and not every patient needs them or is a good fit for them. Your doctor makes the choice.

What is each session like?

You lie on a table, and the radiation therapist positions you using the marks and exact settings. Then they leave the room, because the machine is run from another room. They can see you on camera and talk to you through a microphone. If something is wrong, wave your hand or call out; the machine can be stopped at any moment.

You need to stay still and breathe normally. You may hear the machine, but you do not feel heat, burning, or pain. The radiation itself takes a few minutes, and the whole session usually takes no more than half an hour.

Will I be radioactive? Not with external beam radiation. The beam is only on while the machine is running, and it does not stay in your body. You can be around other people, including children, without worry.

Common side effects and how to care for yourself

Side effects depend on the area being treated and usually build up gradually over the weeks of treatment. The most common are:

Fatigue. This is the most common side effect. Rest, walk as much as you can, and save important tasks for the hours when you have more energy.
Skin changes. Redness, dryness, itching, or peeling, like a sunburn. Wash your skin gently, wear loose cotton clothing, and use only creams your treatment team has approved. Do not wipe off the marks on your skin.
Side effects specific to each area. Examples are mouth sores or trouble swallowing in head and neck treatment, or diarrhea and frequent urination in pelvic treatment. You can find more in the “Side effects by area” guide.

Most short-term side effects slowly get better after treatment ends. Some side effects show up later, and your doctor will follow you for them.

When to call right away

Call your treatment team or doctor if you:

Have a fever of 38 degrees Celsius (100.4 degrees Fahrenheit) or higher
Have skin that is blistered, has an open sore or drainage, or has become very painful and burning
Cannot eat or drink, or have severe vomiting or diarrhea
Have bleeding, including blood in your urine or stool
Have new or worsening trouble breathing, or chest pain

If you have severe trouble breathing, severe chest pain, a seizure, or a drop in alertness, go to the emergency room without delay or call 115 (Iran’s emergency number).