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Radiation Therapy

Radiation therapy is the use of high-energy radiation to damage and kill cancer cells. Unlike the weaker radiation used for routine x-rays, radiation therapy uses specialized, high-energy x-rays, gamma rays, electrons or protons to kill and shrink tumors. Other names include radiotherapy, irradiation, RT, or x-ray therapy.

Radiation Therapy and Cancer Treatment

More than half of people with cancer get radiation therapy. In most cases, the goal of radiation therapy is to cure or stop the growth of cancer. Radiation therapy is often used with other treatments like surgery and chemotherapy. When radiation therapy is used before surgery or chemotherapy, it may make the tumor smaller so these other therapies work more effectively. Radiation therapy can also be used after surgery or chemotherapy to kill any remaining cancer cells. Sometimes radiation therapy is used during surgery to directly target the cancer without passing through skin or other normal, healthy tissue (called “intraoperative radiation therapy”).

When a cure is not possible, radiation therapy can be used to relieve symptoms like pain or pressure by shrinking the cancer (called “palliative radiation therapy”). For some types of cancer, radiation therapy can be given to prevent cancer from growing in the area that receives radiation treatment (called “prophylactic radiation”).

How Radiation Therapy Works

Radiation therapy works by damaging the genetic material and envelope of cancer cells, which stops them from growing and dividing. Normal cells may also be damaged by radiation, but almost always recover after treatment is over, unlike cancer cells.

The goal of radiation therapy is to damage and kill as many cancer cells as possible while limiting injury to surrounding, healthy tissue. This is achieved in a number of ways:

Dosing – The optimal dose of radiation is chosen to cause the most damage to cancer cells while limiting damage to healthy cells.

Targeting – Current technologies allow radiation to be very precisely aimed at the cancer target while sparing surrounding normal tissue. Intensity-modulated radiation therapy (IMRT), 3-D conformal therapy, and stereotactic techniques are a few examples of this new technology.

Scheduling – Radiation therapy can be spread out in small doses over several weeks to allow normal, healthy tissues to repair themselves naturally while the cancer cells die.

Medications – Certain medications can be used during radiation therapy to protect normal tissue, like the glands that make saliva which can be more prone to side effects during radiation therapy (radioprotectors).


A team of health care providers works together to deliver radiation therapy. These include:

  • Radiation oncologist – a doctor who specializes in using radiation therapy to treat cancer
  • Oncology nurse – a nurse who has special training to work with cancer patients
  • Radiation physicist and a dosimetrist – who help design the radiation treatment plan and dose
  • Radiation therapist – who delivers the prescribed treatment
  • Other supportive providers – eg: dietitian, physical therapist, social worker, etc.

Because there are many different types of radiation therapy and different ways to deliver it, treatment planning is an important first step in deciding the type and amount of radiation to give.

External Radiation Therapy

Radiation is often given from a machine outside the body that aims beams of radiation directly at the cancer (called “external-beam radiation therapy”). For patients who receive external radiation therapy, a simulation procedure is done first. Here, the patient lies still on an examining table while the exact target for radiation is determined using imaging machines (x-ray, CT, MRI) that locate the tumor. The areas that will receive radiation are identified on simulation films. Tattoos or markings are placed on the skin to ensure the patient is properly positioned. Depending on the area being treated, the radiation therapist may make body molds or individualized face masks to help the patient keep the same position during each treatment. After the simulation, the team will meet to plan the best way to deliver the radiation treatment. They will follow you closely throughout the course of your treatment and after its completion to monitor for side effects and to ensure coordinated, appropriate care.

Internal Radiation Therapy

Sources of radiation can also be put inside or on the body, in or near the cancer (called “internal radiation therapy” or “brachytherapy”). The radiation sources are radioactive isotopes that are sealed in tiny seeds or pellets. The source is then placed in or near the tumor through a needle, catheter, or another delivery method. There are several internal radiation therapy techniques for different types of cancers.

Systemic Radiation Therapy

A patient is injected or swallows a radioactive substance. The radioactive substance goes through the body, locates and kills the tumor.

Side Effects

Radiation therapy specifically targets the site of the cancer, so the side effects of radiation depend on the area being treated, the dose and type of radiation used, and the individual patient. Side effects are promptly managed during treatment and most go away after treatment is complete. Side effects may include:

  • Fatigue
  • Hair loss
  • Skin changes
  • Nausea
  • Vomiting
  • Loss of appetite
  • Diarrhea
  • Taste changes

There may be some chronic side effects that occur months or years after radiation treatment, depending which part of the body is being treated, like:

  • Memory loss
  • Bowel damage
  • Infertility
  • Fibrosis
  • Second cancer due to radiation exposure

After Treatment – Patients are Not Radioactive

Giving external radiation therapy does not make the patient radioactive. Patients do not have to remain isolated or avoid being around other people because of their treatment. Internal radiation therapy (or brachytherapy) does give off radiation, so the patient may need to stay for a time in the hospital with certain precautions. However, because the radioactivity is mainly around the radiation source itself, the patient’s whole body is not radioactive.

Source: National Cancer Institute – Radiation Therapy for Cancer

For more information:

Go to the Cancer health topic.