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Radiation therapy

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The use of high-energy radiation from x-rays and other sources to kill cancer cells, shrink tumors, and treat other conditions.

Radiation therapy for cancer
Radiation therapy for cancer

How it works

  • At high doses, radiation therapy kills cancer cells or slows their growth by damaging their DNA.
  • Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and removed by the body.

Mechanism of action

Radiation therapy does not kill cancer cells right away. It takes days or weeks of treatment before DNA is damaged enough for cancer cells to die. Then, cancer cells keep dying for weeks or months after radiation therapy ends.

Types of Radiation Therapy

There are two main types of radiation therapy, external beam and internal.

The type of radiation therapy that you may have depends on many factors, including:

  • The type of cancer
  • The size of the tumor
  • The tumor’s location in the body
  • How close the tumor is to normal tissues that are sensitive to radiation
  • Your general health and medical history
  • Whether you will have other types of cancer treatment
  • Other factors, such as your age and other medical conditions
Man prepared for radiation therapy
Man prepared for radiation therapy

External Beam Radiation Therapy

  • External beam radiation therapy comes from a machine that aims radiation at your cancer.
  • The machine is large and may be noisy.
  • It does not touch you, but can move around you, sending radiation to a part of your body from many directions.
  • External beam radiation therapy is a local treatment, which means it treats a specific part of your body.
  • For example, if you have cancer in your lung, you will have radiation only to your chest, not to your whole body.

Internal Radiation Therapy

  • Internal radiation therapy is a treatment in which a source of radiation is put inside your body. The radiation source can be solid or liquid.
  • Internal radiation therapy with a solid source is called brachytherapy. In this type of treatment, seeds, ribbons, or capsules that contain a radiation source are placed in your body, in or near the tumor. Like external beam radiation therapy, brachytherapy is a local treatment and treats only a specific part of your body.
  • With brachytherapy, the radiation source in your body will give off radiation for a while.
Radiation therapy
Radiation therapy

Systemic radiation therapy

  • Internal radiation therapy with a liquid source is called systemic therapy. Systemic means that the treatment travels in the blood to tissues throughout your body, seeking out and killing cancer cells. You receive systemic radiation therapy by swallowing, through a vein via an IV line, or through an injection.
  • With systemic radiation, your body fluids, such as urine, sweat, and saliva, will give off radiation for a while.

Radiation-Based Drugs Emerging as Cancer Therapies

Radiopharmaceuticals deliver radiation therapy directly and specifically to cancer cells.

Radiation Therapy uses

  • Radiation therapy is used to treat cancer and ease cancer symptoms.
  • When used to treat cancer, radiation therapy can cure cancer, prevent it from returning, or stop or slow its growth.
  • When treatments are used to ease symptoms, they are known as palliative treatments. External beam radiation may shrink tumors to treat pain and other problems caused by the tumor, such as trouble breathing or loss of bowel and bladder control. Pain from cancer that has spread to the bone can be treated with systemic radiation therapy drugs called radiopharmaceuticals.

Types of Cancer that Are Treated with Radiation Therapy

  • External beam radiation therapy is used to treat many types of cancer.
  • Brachytherapy is most often used to treat cancers of the head and neck, breast, cervix, prostate, and eye.
  • A systemic radiation therapy called radioactive iodine, or I-131, is most often used to treat certain types of thyroid cancer.

Another type of systemic radiation therapy, called targeted radionuclide therapy, is used to treat some patients who have advanced prostate cancer or gastroenteropancreatic neuroendocrine tumor (GEP-NET). This type of treatment may also be referred to as molecular radiotherapy.

Patient prepared for radiation therapy
Patient prepared for radiation therapy

Combined radiation therapy

  • For some people, radiation may be the only treatment you need. But, most often, you will have radiation therapy with other cancer treatments, such as surgery, chemotherapy, and immunotherapy. Radiation therapy may be given before, during, or after these other treatments to improve the chances that treatment will work. The timing of when radiation therapy is given depends on the type of cancer being treated and whether the goal of radiation therapy is to treat the cancer or ease symptoms.

Combined with surgery

  • Before surgery, to shrink the size of the cancer so it can be removed by surgery and be less likely to return.
  • During surgery, so that it goes straight to the cancer without passing through the skin. Radiation therapy used this way is called intraoperative radiation. With this technique, doctors can more easily protect nearby normal tissues from radiation.
  • After surgery to kill any cancer cells that remain.

Lifetime Dose Limits

There is a limit to the amount of radiation an area of your body can safely receive over the course of your lifetime. Depending on how much radiation an area has already been treated with, you may not be able to have radiation therapy to that area a second time. But, if one area of the body has already received the safe lifetime dose of radiation, another area might still be treated if the distance between the two areas is large enough.

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