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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. The cells most affected are rapidly dividing cells, such as skin cells, cells lining the mouth and gastrointestinal (GI) tract or blood cells in the bone marrow.

Side effects can occur with any type of treatment, but not everyone has them or experiences them in the same way. General side effects of radiation therapy can occur when radiation is given to any area of the body, but will depend mainly on:

  • the specific area or organs being treated
  • the size of the area being treated
  • the type of radiation therapy
  • the amount of radiation given
  • the treatment schedule
  • a person’s overall health
  • other medicines the person is taking
    • Other medicines include:
      • prescription and over-the-counter drugs, including creams and ointments
      • vitamin or mineral supplements
      • herbal remedies and other natural health products
      • complementary and alternative therapies
    • Taking other medicines during radiation therapy may:
      • cause side effects or make the side effects of radiation therapy worse
      • affect how well radiation therapy works

Side effects can happen any time during, immediately after or a few days or weeks after radiation therapy. Most side effects generally go away within 2 months of finishing treatment. However, some side effects may continue after treatment is over because it takes time for healthy cells to recover from the effects of radiation therapy. Late side effects can occur months or years after treatment. If doses of radiation are high enough, some cells may not be able to repair themselves. As a result, some side effects may last a long time or be permanent.

It is important to report side effects to the radiation therapy team. Many side effects can be relieved by medications, a change in diet or other measures. Doctors may also grade (measure) how severe certain side effects are. Sometimes radiation treatments need to be adjusted if side effects are severe.


Fatigue is one of the most common side effects of radiation therapy. Fatigue may be caused by anemia, poor appetite or depression. It may also be related to toxic substances that are produced when cancer cells break down and die. During radiation therapy, the body uses more energy to heal itself, so fatigue will not always be relieved by rest. Making frequent, daily trips for radiation treatments can also be tiring.

Radiation therapy to any area of the body can make a person feel more tired than usual, but fatigue is more common when larger areas of the body are treated. Anemia is more likely to occur when the treatment area includes where blood cells are formed in the bone marrow, such as the pelvic bones.

Fatigue usually occurs during or after the second week of radiation therapy. Symptoms of fatigue may increase or become more severe over the course of treatment. Fatigue usually goes away gradually after treatment has ended, but some people continue to feel tired for several weeks or months after radiation therapy.

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Skin reactions

Skin reactions occur because external beam radiation travels through the skin to reach the area being targeted for treatment. The skin in the radiated area may become red, dry or itchy. It may change colour (become darker or tanned looking). Most skin reactions occur within the first 2 weeks of receiving radiation therapy. They usually go away a few weeks after treatment, but some skin changes, like skin darkening or scarring, can be permanent. Some people do not experience any skin reactions with radiation therapy.

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Changes in appetite

Radiation therapy can affect a person’s appetite in a number of ways. Radiation therapy to the head and neck area can cause temporary changes in taste or smell, which can make foods seem less appetizing. Some people lose interest in food completely and don’t eat, even though they know they need to. Loss of appetite is a common problem and can lead to weight loss. Some people may gain weight from frequent snacking to control nausea during treatment.

Loss of appetite typically occurs after side effects like mouth sores, dry mouth, difficulty swallowing and nausea or vomiting develop (about 2–3 weeks into treatment). It may continue for 2–3 weeks or longer after treatment has ended. Maintaining good nutrition during and after radiation therapy is important to help a person recover from treatment.

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Hair loss

Hair loss (alopecia) only occurs in the area being treated with radiation therapy. Thinning or loss of hair can occur in any area where radiation is directed. The extent of hair loss and regrowth varies from person to person and depends on the dose of radiation.

Hair loss can begin about 2–3 weeks after radiation therapy starts. Smaller doses of radiation usually result in temporary hair loss. Permanent hair loss is more common at higher doses. When hair regrows, usually about 3–6 months after radiation therapy is finished, the colour or texture may be different and it may grow back thinner or patchy.

Hair should not be permed, straightened, dyed or coloured during treatment. These products contain chemicals that can damage hair. It is best to wait until new hair growth becomes established and hair returns to its original state. Ask the radiation therapy team about when it is okay to use these products again.

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Radiation sickness

Radiation sickness is characterized by loss of appetite, nausea and vomiting. This is a common side effect if the stomach and abdomen are in the treatment area. It can also occur as a general side effect regardless of the area being treated. Radiation sickness is due to toxic substances that are released when tumour cells break down and die. Radiation sickness usually goes away a few weeks after external beam radiation therapy is finished.

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Bone marrow suppression

Bone marrow suppression is a condition in which one or more of the main types of blood cells are decreased.

  • A low white blood cell count (neutropenia or leukopenia) increases the risk of infection.
  • A low platelet count (thrombocytopenia) increases the risk of bruising and bleeding.
  • A low red blood cell count (anemia) causes fatigue, paleness and malaise. (Radiation therapy doesn’t usually affect red blood cells very much, except when there is bleeding and blood loss.)

Low blood cell counts occur because of radiation’s effect on blood cells made in the bone marrow. Blood cell counts are more likely to be affected if:

  • a person receives chemotherapy at the same time as radiation therapy
  • the pelvic bones (where many of an adult’s blood cells are made) are in the treatment area
  • total body irradiation (TBI) is given before a stem cell transplant

Drops in blood cell levels are rarely severe enough to cause problems. When there is a break from treatment for a few days, blood cell counts usually recover.

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Reduced bone growth

Reduced bone growth occurs because of radiation’s effect on the rapidly dividing immature cells of bones that lie in the treatment area. This is most noticeable in very young children because most of their bones have not matured to the point where they can withstand radiation. The child’s height or limb length can be shortened. Scoliosis (curved spine), kyphosis (hunchback) or spinal shortening can also occur. In addition, bones treated with radiation tend to break easily.

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Anxiety or depression

Each person reacts differently to a cancer diagnosis and will cope in different ways. Starting radiation therapy can lead to new worries and fears and may cause anxiety, sadness and depression. If you have these feelings most days, tell the healthcare team. They may prescribe medications or refer you to a professional, such as a social worker or psychologist.

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Sleep problems

Sleep problems, especially insomnia, are common during treatment. Signs of insomnia include:

  • being unable to fall asleep
  • waking up often during the night
  • waking up very early and being unable to go back to sleep
  • feeling sleepy during the daytime

Pain, anxiety, depression and some medications can affect sleep patterns. If you have problems sleeping during radiation therapy treatments, tell the healthcare team.

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Changes in sexuality

Some people may experience changes in their feelings about and attitudes toward sexuality as they go through radiation therapy. Some people are less interested in sex because of the physical and emotional stresses of having cancer and getting radiation therapy. Stresses may include:

  • being worried about changes in appearance
  • coping with side effects of treatment, including fatigue and hormonal changes
  • feelings of anxiety about health, family or finances

A partner’s fears and concerns may also affect the sexual relationship. Try to share feelings with each other and with the healthcare team. If talking about sex, cancer or both is difficult, a counsellor may be able to help develop a more open discussion.

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Second cancers

A very small number of people develop a second cancer caused by radiation therapy. The benefit of treating a person’s cancer usually far outweighs the risk of developing a second cancer from radiation therapy. People who receive both chemotherapy and radiation therapy have the highest risk of developing a second cancer. A second cancer can develop a few years after radiation treatment, but most do not occur for 10–20 years or more after treatment.

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gastrointestinal (GI)

Referring to or having to do with the digestive organs.

The gastrointestinal (GI) tract, or digestive tract, includes the mouth, pharynx (throat), esophagus, stomach, small intestine and large intestine.


Brock Taraba Brock has been cancer free for over a decade, thanks to the support we received from the Canadian Cancer Society.

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Some cancers, such as thyroid and testicular, have survival rates of over 90%. Other cancers, such as pancreatic, brain and esophageal, continue to have very low survival rates.

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