Radiation Therapy


What Is It?

Radiation therapy is a form of cancer treatment that uses ionizing radiation (an intense form of energy) to damage or destroy cancer cells. Ionizing radiation attacks cancer cells by harming their genetic material, which kills them or interferes with their ability to grow and multiply. During radiation therapy, normal cells located near the cancer cells can be damaged as well, but these usually are able to recover and survive.

Radiation therapy can be given externally in the form of X-ray beams, gamma rays or beams of subatomic particles. Treatment with external radiation is usually painless and takes five to 15 minutes per session. The number of treatments varies for each person. In some cases, therapy can take several weeks of closely scheduled sessions.

Radiation also can be delivered internally. Radioactive substances either are placed inside a body cavity or implanted inside the tumor itself.

Some innovations that can increase the effectiveness of radiation therapy include:

  • Conformal beam techniques — Radiation is delivered from many beams at the same time. This allows the radiation to be concentrated on the tumor with less damage to nearby normal tissues.
  • Intraoperative radiation therapy — Radiation is delivered to a tumor during surgery.
  • Radiosensitizers — These drugs increase radiation’s damaging effect on cancer cells.
  • Radioprotectors — These drugs protect normal cells from radiation damage, while nearby cancer cells are destroyed.
  • Radioimmunotherapy — Radioactive substances are attached to antibodies, which are defensive chemicals made by the body’s immune system. These antibodies specifically target cancer cells and deliver damaging radioactivity only to them. Because the antibodies do not attack noncancerous, healthy cells, this reduces the potential for radiation damage outside the tumor.

What It’s Used For

Radiation therapy is used to treat many types of cancer, including cancer of the lung, breast, prostate, testicles, lymphoid tissues and brain.

When a tumor is going to be removed surgically, radiation also can be used first to help shrink the tumor and to reduce the amount of normal tissue that needs to be removed near the tumor. When cancer has spread, radiation therapy can be combined with chemotherapy or surgery to give a better chance for a cure, or to help reduce symptoms that are caused by the cancer spreading to other areas.


Because radiation therapy can affect your teeth, you should visit your dentist to have any major dental work done before beginning radiation treatments to the head and neck. Also, because radiation of certain body areas can increase your risk of infertility or sterility, you should discuss family-planning issues with your doctor, including the option of sperm banking. You also should check with your doctor before therapy to see if any of your current medications could cause problems during radiation therapy. As with chemotherapy, if you are a woman and there is a possibility that you might be pregnant, you should tell your doctor before starting treatment.

Because radiation therapy can make you feel tired, you might consider reducing your work schedule or taking vacation time during treatments. You also might want to arrange for a friend or family member to drive you to therapy.

Because radiation therapy can irritate skin in the treatment area, you should wear loose clothing that doesn’t rub or bind.

How It’s Done

Before beginning external radiation therapy, the radiation specialist will plan how your treatments will be done, including the type of radiation, dose and the number of treatment sessions. You will participate in a simulation session to help the specialist plan the treatment. He or she might mark the area of your body with tiny permanent or semi-permanent tattoos.

Depending on the body area to be treated, you might need to remove your clothing and put on a hospital gown. In the radiation-therapy room, you either will lie on a treatment table or sit in a special chair. The marks on your skin will be used to guide the therapist in locating the precise area to be treated, and in placing special blocks and shields to protect other parts of your body. It’s very important that you remain still during treatment and that you are placed in the same position every time you are treated so the radiation will be delivered to the same location each time. For this reason, a mold may be made of a portion of your body, and you will be placed in the mold for treatment. Once you are ready for your treatment, the radiation therapist will leave the room and go to a control room nearby. From there, the therapist will operate the treatment machine while he or she watches you on a monitor or through a special window. During radiation therapy, you might hear the treatment machine make a buzzing noise, and the machine itself might rotate around you. Treatments typically are brief and painless, normally lasting one to five minutes. Your total time in the treatment room usually will be five to 15 minutes. Usually, treatments will be given every weekday for several weeks.

If you are having internal radiation therapy, your treatment will be done differently. If you are having brachytherapy, also known as interstitial radiation therapy or “seeds,” you will be given anesthesia, and radioactive material (contained in wires or small tubes) will be implanted either directly into your tumor or into a nearby area. These radioactive implants either will remain inside your body or be removed after a period of time, which varies depending on the cancer. In intracavitary therapy, you will be given a general or local anesthetic, and radioactive material will be placed directly inside a body cavity such as the uterus, vagina or rectum. This material later will be removed.


Doctors use physical exams, scans, X-rays and blood tests to evaluate the progress of your radiation therapy. Your specific type of follow-up testing will vary depending on the type of tumor and the degree of cancer spread.


Radiation therapy has many possible side effects, which vary depending on the specific body area being treated. These include fatigue, skin irritation, temporary or permanent hair loss, temporary change in skin color in the treatment area, loss of appetite, nausea and vomiting, sluggish bowels, cramps and diarrhea, infertility or sterility, vaginal dryness or narrowing, and impotence. Radiation therapy also can increase your risk of developing a second cancer.

When To Call A Professional

Call your doctor immediately if skin in the treatment area becomes painful, bright red, moist and weepy. Your doctor can give you medication to relieve skin pain and to prevent infection in the irritated area. If your throat or mouth becomes sore, you can ask your doctor about special mouthwash medication (also used for gargling) to make eating and swallowing more comfortable. Also, if you are having nausea, vomiting or diarrhea, call your doctor for medication to treat these symptoms.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.