Radiation therapy

Radiation is energy that moves through space. Radiation can be given off naturally, like from sunshine and, in low doses, from the earth and rocks.

Radiation can also be produced artificially by machines. In lower doses, it is used for things like x-rays, to take pictures of the inside of your body.

Radiation therapy to treat cancer uses much higher doses of radiation to destroy cancer cells. It damages the cancer cells over and over again. The cancer cells don’t have time to repair themselves between daily treatments so eventually they die.

How radiation therapy works

Radiation therapy works by destroying cancer cells and damaging a cancer cell’s DNA so that it stops dividing and growing. Radiation therapy can shrink a tumour or completely destroy it. It is most effective on cells that grow and divide quickly. Cancer cells tend to divide more quickly than most normal cells. This makes them more likely to be affected by the radiation (be radiosensitive) than normal cells.

Even though cancer cells and normal cells react differently to radiation, it’s very hard to destroy cancer cells without damaging some normal cells too. Damage to normal cells causes side effects. Normal cells are often able to recover better from radiation damage than cancer cells. The goal of radiation therapy is to give enough radiation to destroy cancer cells in your body but not so much that normal cells can’t recover.

How radiation therapy is used

Radiation therapy may be used alone to treat cancer or with other treatments such as surgery or chemotherapy. It may be used before surgery to shrink a tumour or after surgery to destroy any cancer cells that remain and to prevent the cancer from coming back. Radiation therapy may also be used to relieve symptoms, improve quality of life and extend life for people living with advanced cancer (called palliative radiation therapy).

External radiation therapy (also called external beam radiation therapy) is the most common type of radiation therapy used to treat cancer. A machine directs a beam of radiation at a cancerous tumour in the body. There are different types of external radiation therapy.

Internal radiation therapy puts radioactive substances into the body, such as directly into the tumour or into an area of the body, to kill the cancer cells. There are different types of internal radiation therapy.

Going for radiation treatments

Radiation therapy is given in the radiation therapy department of a cancer treatment centre, and usually you’ll be an outpatient. This means that you won’t have to stay overnight. Your first appointment is often with the radiation oncologist. They will go over your medical records, will do a physical exam and may order tests. They will discuss radiation therapy, treatment options and side effects. If you have any questions about radiation therapy and your treatment, you can ask the radiation oncologist.

Radiation therapy often involves a team of healthcare professionals:

Radiation oncologist is a doctor who specializes in treating cancer with radiation therapy. They will order your radiation treatment, develop a treatment plan and oversee your treatments. They work closely with the rest of the radiation therapy team.

Radiation oncology nurse takes care of you while you are receiving radiation therapy.

Medical physicist works with a radiation oncologist to plan your radiation treatment. They make sure the radiation therapy is delivered safely and the equipment and computer systems work properly.

Dosimetrist develops the treatment plan and calculates the amount (dose) of radiation you will receive based on your treatment plan.

Radiation therapist operates the radiation machines. They give you your daily treatment. They also work closely with radiation oncologists and the rest of the team to carry out your treatment plan.

Expert review and references

  • American Cancer Society. A Guide to Radiation Therapy. 2015.
  • American Society of Clinical Oncology. What to Expect When Having Radiation Therapy. 2016.
  • BC Cancer Agency. Radiation Therapy. BC Cancer Agency; 2017.
  • Radiotherapy. Cancer Research UK. CancerHelp UK. Cancer Research UK; 2009.
  • Kun, L. E . General principles of radiation oncology. Pizzo, P. A. & Poplack, D. G. (Eds.). Principles and Practice of Pediatric Oncology. 6th ed. Philadelphia: Lippincott Williams & Wilkins; 2011: 13: pp. 406-425.
  • National Cancer Institute. FactSheet: Radiation Therapy for Cancer. Bethseda, MD: National Cancer Institute; 2010.
  • Princess Margaret Cancer Centre. Your Radiation Therapy at the Princess Margaret Hospital. 2011.
  • Radiological Society of North America. Introduction to Cancer Therapy (Radiation Oncology). 2015.
  • Radiological Society of North America. Professions in Radiation Therapy. 2015.

External radiation therapy

External radiation therapy is also called external beam radiation therapy. It is the most common type of radiation therapy used to treat cancer. A machine directs a beam of radiation through the skin to a specific part of the body.

Internal radiation therapy

Internal radiation therapy places radioactive materials in the body. A larger dose of radiation can be given with internal radiation therapy than with external radiation therapy. Radiation can be given directly to cancer cells and so less radiation goes to nearby normal tissue. But internal radiation therapy can only be used to treat certain types of cancer.

Side effects of radiation therapy

Radiation therapy damages cancer cells. Healthy cells in the treatment area can also be damaged, even though steps are taken to protect normal tissue as much as possible. Side effects are caused by damage to healthy cells. Different cells and tissues in the body tolerate radiation differently.

Caring for yourself during radiation therapy

Having radiation therapy will most likely affect you and your family's day-to-day life. Caring for yourself during radiation therapy is important. You may have general side effects of radiation therapy along with other effects, depending on what part of your body is being treated. Learn ways to cope during radiation therapy.

Medical disclaimer

The information that the Canadian Cancer Society provides does not replace your relationship with your doctor. The information is for your general use, so be sure to talk to a qualified healthcare professional before making medical decisions or if you have questions about your health.

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