Side Effects of Radiation Therapy

The goal of radiation therapy (also referred to as radiotherapy) is to eliminate cancerous tumors within the body without destroying the surrounding healthy tissue. This type of therapy is used in the treatment of many cancers, even those previously considered inoperable (not treatable with surgery), such as brain or throat cancers. New developments have led to even more effective forms of radiation therapy, such as three-dimensional conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT), and proton beam therapy. However, undesired side effects may accompany even the most precise therapy. Side effects occur because within the treatment area, radiation therapy affects any rapidly reproducing cells, not just cancer cells, and also may shrink local blood vessels. Side effects caused by scarring can also occur as the body heals. The medical goal of radiation therapy is to minimize side effects while maximizing cancer cell death. Many unwanted symptoms of radiation therapy are controlled or relieved with medications, diet, and stretching/exercise, and many problems disappear when treatments are completed.

Common side effects of radiation therapy

Radiation therapy, as described in
PLWC Feature: Part I: Understanding Radiation Therapy, uses directed and invisible packets of energy to treat cancer. Radiation therapy can be thought of as a localized, invisible, and intense “sunbeam” focused on your cancer. Not surprisingly, a common side effect of radiation treatment is a sunburn-type reaction in the skin through which the radiation beam passes. Other common side effects include fatigue (tiredness) and loss of appetite. For more information about fatigue, please read PLWC Feature: Coping With Cancer-Related Fatigue.

For some people, radiation therapy causes little or no side effects. For others, the side effects are more severe. The side effects of radiation therapy vary from person to person and also with the type and location of cancer, treatment dose, and the individual's general health.

Side effects, if experienced, often begin by the second or third week of treatment and may last for several weeks after the final radiation treatment, although there is significant variation depending upon the type of side effect. Occasionally, long-term side effects occur. These include infections, impotence (the inability to achieve or maintain an erection), infertility (the inability to become pregnant or conceive a child), and secondary cancers. These problems usually do not arise for months or even years after radiation therapy, but they are more likely to be permanent and serious. Your radiation oncologist and radiation oncology nurse specializes in radiation therapy and will work with you to ease or prevent many of these side effects.

Misconceptions about radiation therapy

The following statements are misconceptions about radiation therapy and comments about actual facts:

Myth: Radiation therapy is painful.
Fact: The treatments are usually short, painless, and quiet, except for the noises from the machines.

Myth: All patients experience unpleasant reactions after radiation therapy.
Fact: Many patients have mild or no side effects. For those that do not experience side effects, these can often be managed with the help of your oncologist.

Myth: Radiation therapy causes people to "glow," and there is a risk of exposing others to radiation.
Fact: You will not be radioactive following external-beam radiation therapy, although certain precautions need to be followed to reduce exposure to others if you receive internal radiation therapy (brachytherapy or radioactive isotopes).

Myth: Radiation therapy causes baldness.
Fact: You will not lose your hair except in areas where the radiation is focused.

Myth: Radiation therapy causes infertility.
Fact: Only radiation therapy aimed at the ovaries or the testicles carries a risk of infertility. It is recommended that you discuss the risk of infertility associated with the treatment of your particular cancer with your doctor.

Myth: Radiation therapy causes cancers later in life.
Fact: While radiation therapy can contribute to a secondary cancer, the risk is low. The potential benefits versus risks of treatment always must be considered. Talk with your doctor about your individual risk.

Site-specific side effects

Head and neck

Side effects of radiation therapy to the head and neck may include mouth sores, lack of or thickened saliva, difficulty swallowing, stiffness in the jaw, and nausea. Your medical team can help reduce any discomfort you may have, but only if you report what you are experiencing. Cavities in your teeth and dryness, soreness, and infections in your mouth can be particularly problematic; these can be lessened somewhat by taking good care of your mouth and teeth. It is particularly important for patients receiving radiation therapy to the head and neck to visit their dentist for a thorough oral examination several weeks prior to treatment. This time frame allows healing if any invasive dental procedures are necessary.

To help manage the side effects associated with head and neck radiation therapy, avoid spicy and acidic foods; do not smoke, chew tobacco, or drink alcohol; and brush your teeth and gums at least four times a day using fluoride toothpaste on a soft brush. Many of these symptoms will disappear within a month after treatments have ended, but mouth dryness may be permanent. Artificial saliva and medication can help to ease this problem.

A particularly debilitating side effect called osteoradionecrosis affects 3% to 10% of people with head and neck cancer. This occurs when radiation therapy reduces blood flow to jaw bones, making them susceptible to infections. Adequate nutrition and proper oral hygiene are necessary to avoid or reduce the osteoradionecrosis.


Radiation therapy to the chest may cause difficulty swallowing, cough, fever, shortness of breath, breast or nipple soreness, and shoulder stiffness, as well as fatigue and skin irritation. A few people develop a cough, fever, and fullness of the chest that is diagnosed as radiation pneumonitis, an inflammation of the lung occurring between two weeks to six months after radiation therapy. Although sometimes very mild, radiation pneumonitis may lead to permanent scarring of the lungs called radiation fibrosis, which is associated with more serious heart and lung problems.

Stomach and abdomen

Side effects from radiation therapy to the stomach and abdomen include queasiness, nausea, or diarrhea. These symptoms will likely disappear when treatment is completed. Your doctor can prescribe medications for these side effects, and changes to your diet can also reduce your discomfort. For more information, please read
PLWC Feature: Managing Cancer Side Effects Through Nutrition.


Digestive problems and bladder irritation can result from radiation of the pelvic region. Drinking fluids (not alcohol or caffeinated drinks) can help relieve some of these issues. Again, your doctor will help you manage these side effects.

Most people who received radiation therapy of the pelvis worry about losing sexual and reproductive abilities. Some women receiving high doses of radiation therapy may stop menstruating and experience symptoms of menopause, such as vaginal itching, burning, and dryness. Permanent infertility can occur, but generally only if both ovaries receive radiation therapy. Men receiving radiation therapy to the testes will have lowered sperm counts and reduced sperm activity that affects fertility. Sexual performance of both men and women can be affected, although most types of radiation therapy will not directly impact the practice or enjoyment of sexual intercourse. Instead, the level of desire may decrease. This can be due more to the stress of having cancer rather than to the effects of radiotherapy. Sexual desire often returns once treatment ends.

Of particular concern are the side effects of radiation therapy to the prostate. The location of the prostate means that radiation treatment to this area may affect functioning of the rectum, bladder, and penis. Side effects may include diarrhea, rectal bleeding, incontinence, and in approximately one-fourth to one-half of patients, an inability to obtain an erection within a year following radiation therapy. Radiation therapy seems to gradually decrease functioning of the nerves and blood vessels that control erection. In particular, scarring may affect the elasticity of arteries involved in creating an erection. Some of the radiation therapy side effects listed above will resolve (go away) in a few weeks. Others may last a year or two after treatment, and some, such as impotence, can be permanent. Medication and other treatment options may be helpful. Major improvements in radiation technology enable very precise targeting of radiation, such that treatments result in fewer side effects. It is recommended you speak with your radiation oncologist to minimize the occurrence and impact of these side effects. For more information, please see the
Sexuality section.

Additional resources

National Cancer Institute (NCI):
Radiation Therapy and You

American Cancer Society (ACS):
Radiation Therapy Effects

Head and neck cancer

Oral Complications of Chemotherapy and Head/Neck Radiation

Chest cancer

Lung Cancer Online:
Radiation Side Effects
5 Radiation Myths and Radiation Side Effects

Radiation pneumonitis


Prostate cancer

Prostate Cancer Foundation:


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