Radiation therapy can cause both early/acute and late/chronic side effects. Acute side effects occur during treatment, and chronic side effects occur months or even years after treatment ends. The side effects that develop depend on the area of the body being treated, the dose given per day, the total dose given, the patient’s general medical condition, and other treatments given at the same time.

Acute Side Effects

Acute radiation side effects are caused by damage to rapidly dividing normal cells in the area being treated. These effects include skin irritation or damage at regions exposed to the radiation beams. Examples include damage to the salivary glands or hair loss when the head or neck area is treated, or urinary problems when the lower abdomen is treated. Most acute effects disappear after treatment ends, though some (like salivary gland damage) can be permanent. Fatigue is a common side effect of radiation therapy regardless of which part of the body is treated. Nausea with or without vomiting is common when the abdomen is treated and occurs sometimes when the brain is treated. Medications are available to help prevent or treat nausea and vomiting during treatment.

Late Side Effects

Late side effects of radiation therapy may or may not occur. Depending on the area of the body treated, late side effects can include:
  • Fibrosis (the replacement of normal tissue with scar tissue, leading to restricted movement of the affected area).
  • Damage to the bowels, causing diarrhea and bleeding.
  • Memory loss.
  • Infertility (inability to have a child).
  • Rarely, a second cancer caused by radiation exposure.
Second cancers that develop after radiation therapy depend on the part of the body that was treated. For example, girls treated with radiation to the chest for Hodgkin lymphoma have an increased risk of developing breast cancer later in life. In general, the lifetime risk of a second cancer is highest in people treated for cancer as children or adolescents. Whether or not a patient experiences late side effects depends on other aspects of their cancer treatment in addition to radiation therapy, as well as their individual risk factors. Some chemotherapy drugs, genetic risk factors, and lifestyle factors (such as smoking) can also increase the risk of late side effects. When suggesting radiation therapy as part of a patient’s cancer treatment, the radiation oncologist will carefully weigh the known risks of treatment against the potential benefits for each patient (including relief of symptoms, shrinking a tumor, or potential cure). The results of hundreds of clinical trials and doctors’ individual experiences help radiation oncologists decide which patients are likely to benefit from radiation therapy.

Manage Radiation Therapy Side Effect Handouts:

Will open a PDF in new window from the National Cancer Institute.