Radiation Therapy: The Basics

Carolyn Vachani, RN, MSN, AOCN
Last Reviewed: November 2, 2018

Cancer is caused by cells growing out of control. As the number of cells grow, they form into a mass or tumor. Cancer cells, which make up the tumor, grow and reproduce very quickly. Normal, healthy cells know to stop reproducing and growing when they touch other cells. Cancer cells do not and keep on growing. 

What is radiation therapy?

Radiation therapy uses high energy x-rays to damage the DNA of cells. This kills the cancer cells, or stops them from reproducing. It is used to treat many types of cancer. It is estimated that 50% of cancer patients will receive radiation during treatment for their cancer. 

Radiation therapy is called a localized treatment. This is because it treats a specific area of the body where the cancer is growing. That is different than a chemotherapy, which is called a “systemic” therapy because it can travel to all areas of the body. There are two main types of radiation therapy:

  • External radiation therapy: a beam of radiation is directed into the body. This may also be called x-ray therapy, 3D conformal radiation, intensity modulated radiation therapy (IMRT), cobalt, photon, or proton therapy.
  • Internal radiation therapy: a source of radioactivity is placed inside the body, near the tumor. This is called brachytherapy or implant therapy.

How is radiation therapy given?

External Radiation

  • Treatment can be given once or twice a day, depending on the treatment plan. 
  • Treatments are often given 5 days a week for many weeks. The number of weeks will depend on the total dose of radiation that is planned. 
  • When radiation is used to treat metastasis (spread of cancer), it is often given in short courses (over a few days).
  • Patients may be given a break from treatment on the weekend. This gives normal cells some time to heal. This can reduce side effects. 
  • Patients receiving external radiation are not radioactive or dangerous to the people around him or her.

Internal Radiation

  • “Seeds” (small pieces of a radioactive substance) are implanted close to the tumor. This delivers a high dose of radiation to a small area of the body. This can prevent nearby healthy tissue from being harmed.
  • The substances used for internal radiation include radium, cesium, iodine and phosphorus.
  • The radioactive implant may be placed short term or can be permanent. The radioactive effect wears off over time.
  • Patients with radiation implants may need to be isolated from family/visitors for a short period of time. This is to protect others from exposure to radiation. 
  • Patients receiving internal radiation will be given safety instructions, based on their treatment.

What are the side effects of radiation therapy?

Radiation can damage normal cells as well as cancer cells. The side effects you may have will be related to the area of the body that is being treated.

The following list includes some of the most common side effects that happen while getting radiation therapy. If side effects become severe, treatment may be put on hold. Treatment may resume when your side effects are managed. Most side effects are short term - occurring while you are on treatment. They tend to go away within a few months after your treatment ends. They can include: 

  • Skin reaction: There may be some reddening of the skin. The area being treated may become irritated, dry, or sensitive. A skin reaction may look like a sunburn. Treat the skin gently to avoid further irritation. Bathe using only warm water and mild soap. Do not use lotions or soaps that have perfume or scent in them. 
  • Hair loss: Hair loss can happen in the area being treated. You will only lose the hair on your head if radiation is directed at the head. In some cases, the hair will not regrow after radiation. Hair that does grow back is often thinner. 
  • Nutritional problems: Radiation can affect the mouth, throat, stomach and/or bowel when these areas are in the radiation field. This can lead to pain with swallowing, changes in how food tastes, nausea, and diarrhea. Medications can be used to treat nausea and diarrhea. Oral rinses and pain medicine may offer some relief for ulcers of the mouth and throat. Over-the-counter mouthwashes should be avoided, as many contain alcohol which can sting. Foods that are soft or soothing to the throat (such as ice cream or water ice) may be helpful.
  • Fatigue: Fatigue is one of the most common side effects of radiation therapy. Try to balance your normal activity with periods of rest. It can take several months or more after treatment ends for fatigue to resolve. 
  • Neutropenia: A neutrophil is a type of white blood cell that fights infection. During radiation treatments, the body's number of neutrophils may be decreased. This is called neutropenia. This puts the patient at a higher risk of getting an infection. Patients and those around them should wash their hands often to lower the risk of getting an infection. Avoid people who are sick (i.e.: have colds). Patients should contact their provider right away if they have a fever (temperature greater than 100.4), sore throat or cold, or a sore that doesn't heal.

Some side effects can happen 5, 10, or more years after treatment. These long-term side effects of radiation occur in the area that was treated. Long-term side effects can include:

  • Issues with memory
  • Muscle weakness
  • Development of another cancer as a result of damage to tissue
  • Cataracts
  • Dental problems 
  • Heart problems (high blood pressure, high cholesterol levels)
  • Inability to have or father children
  • Hypothyroidism 

Speak to your care team about any side effects you are having, whether you are on treatment or years later. Talk with your healthcare team about your specific risks, and how these weigh against the benefits of treatment.

How will I know if radiation is working for me?

There are a number of ways your care team can determine if radiation is working for you. These can include:

  • Imaging Tests: Many patients will have radiology studies (CT scans, MRI scans, PET scans) during or after treatment to see if/how the tumor has responded (gotten smaller, stayed the same, or grown). 
  • Blood Tests: Some tumors are able to be measured in the blood with a "tumor marker". This is a substance that is either made by the tumor or by the body in response to the tumor. If the treatment is working, the tumor marker should decrease.
  • Symptoms: In some cases, a decrease in a patient's symptoms, such as pain, may be a sign that the tumor is shrinking.

Resources for More Information

Learn more about the steps involved in radiation therapy.

Learn more about the different types of radiation.

Learn more about proton therapy.

Learn more about radiation therapy side effects.

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