Part I: Understanding Radiation Therapy

What is radiation?

Radiation has been described as moving packets of energy that are made when subatomic particles (for example, protons, electrons, and neutrons) break apart into pieces. Radiation of different types is used in such things as microwaves, telephones, and televisions, or unleashed to produce the extreme power in a nuclear reactor or—at a much greater level—in the sun. The differences in these forms of radiation have to do with their frequency. Only the highest frequencies of radiation, those defined as ionizing radiation, have the intensity to damage living tissue.

Almost everyone has experienced ionizing radiation in the form of a sunburn from ultraviolet (UV) light. Short exposure to radiation from medical x-rays allows us to view things in our bodies that are denser than skin and tissue, such as bones and teeth, without causing any injury. However, radiation of even higher intensity can penetrate (reach) into cells themselves and disrupt the genetic material in cells that is necessary for cell replication (copying). When the damaged cells die, the body naturally gets rid of them. Radiation therapy (also called radiotherapy) makes use of ionizing radiation as a "bladeless knife" to destroy active cancer cells inside the body.

Radiation as therapy

The goal of radiation therapy is to kill cancer cells without harming the surrounding healthy tissue. Some forms of cancer, such as prostate and larynx cancer, can be successfully treated with radiation therapy as the sole or primary therapy. In other types of cancer, such as breast cancer, radiation therapy is a complementary treatment used along with surgery, chemotherapy, or immunotherapy (biologic therapy). In these cases, radiation therapy represents an extremely important additional, or adjuvant, therapy to the other treatment(s) because of its ability to target specific cells. Even when surgery may remove the cancer completely, or when chemotherapy eliminates detectable cancer cells, the risk remains that a few cancer cells survived and can again cause disease. In cases where successfully treating the cancer is not possible, radiation therapy can be used to shrink tumors and reduce the pressure, pain, and other symptoms of cancer. This is called palliative radiation. More than half of all people with cancer undergo some form of radiation therapy.

Types of radiation therapy

External-beam radiation therapy. The most widely used type of radiation therapy delivers high-energy x-rays or electrons from a machine external to, or outside of, your body. The machine most commonly used is called a linear accelerator, or sometimes, a linac. External-beam radiation therapy allows large areas of the body to be treated, if required. Special software helps direct the beam to effectively treat tumors while sparing the normal tissue surrounding the cancer cells. The treatments occur at the hospital, but require only short visits (approximately 30 minutes) and can be performed on an outpatient basis. External-beam radiation therapy will not make you radioactive.

Three-dimensional conformal radiation therapy (3D-CRT). This new treatment uses special computers to generate detailed three-dimensional pictures of the cancer. More accurately aimed radiation allows higher doses to be used, while reducing radiation damage to healthy tissue. Studies have shown that 3D-CRT can result in decreased risk of complications. The beneficial impact on survival has not been proven.

Proton beam therapy. This type of external-beam radiation therapy makes use of protons rather than x-rays to treat certain cancers. Protons are parts of atoms and possess enough energy to destroy cancer cells when directed to a particular site of cancer in the body. The proton's energy has only a very local effect, such that normal cells in front of and behind the tumor are left mostly unharmed. Although still new, treatment using protons promises to deliver more radiation to the cancer, while reducing the damage to nearby, healthy tissue. Because this therapy requires highly specialized equipment, it is currently only available in a few medical centers.

Neutron beam therapy. Neutron beam therapy uses particles called neutrons from the center of atoms. The effectiveness of neutron beam therapy means that compared with conventional radiation therapy, less than half the radiation sessions are required. This makes neutron beam therapy especially useful with certain inoperable and fast-growing brain tumors.

Stereotactic radiation therapy. Stereotactic radiation therapy delivers a large, precise radiation dose to a small tumor area. Because of the precision involved in this type of treatment, the patient must remain extremely still. Head frames or individual body molds may be made to keep the patient from moving. Although often performed as a single treatment, fractionated radiation therapy, where patients receive multiple treatments, may be necessary.

Internal radiation therapy. Also known as brachytherapy, which means short-distance therapy, internal radiation therapy involves placing radioactive material into the cancer itself or into tissue surrounding it. These implants may be permanent or temporary (lasting several minutes to a few days). Sealed devices containing the radioactive sources can be in the form of thin wire or tubes, ribbons, or capsules (seeds). Internal radiation therapy may require a hospital stay. The sealed sources deliver most of the radiation around the area of the implant, but some radiation can be emitted (sent) from your body. Your whole body does not become radioactive, but certain precautions should be taken to protect hospital staff and visitors from radiation exposure (see Safety for the patient and family).

Other treatment options

Intraoperative radiation therapy (IORT). Radiation therapy can be delivered directly to the tumor during surgery, either as external-beam radiation therapy or as internal radiation therapy. This technique allows normal tissue to be moved out of the way by the surgeon before radiation therapy occurs and is especially helpful when vital, normal organs are dangerously close to the tumor.

Systemic radiation therapy. Systemic radiation therapy uses radioactive materials, such as iodine 131 or strontium 89, that can be taken by mouth or injected into your body and used to treat cancer of the thyroid. These radioactive materials can leave the body through saliva, sweat, and urine, making these fluids radioactive. Additional safety measures must be used to protect people who come in close contact with the patient (see Safety for the patient and family).

Radioimmunotherapy. Proteins called antibodies have been discovered that can bind (stick) to some types of cancer cells while not binding to normal body cells. Recent research makes use of such antibodies by generating them in large quantities in the laboratory and physically attaching radioactive molecules to them to produce radiolabeled antibodies. When injected into the body, these radiolabeled antibodies deliver doses of radiation directly to the tumor. Because the original antibodies come from cells of the immune system, this therapy is called radioimmunotherapy.

Example: ibritumomab tiuxetan (Zevalin), tositumomab (Bexxar)

Radiosensitizers and radioprotectors. Researchers are studying radio sensitizing and radioprotectant substances that help radiation better destroy tumors or better protect normal tissues near the area being treated.

Example of radiosensitizers: fluorouracil (5-FU), cisplatin (Platinol)
Example of a radioprotector: amifostine (Ethyol)

Safety for the patient and family

Radiation comes from a source, but a person does not become radioactive when receiving external-beam radiation therapy. The radiation remains in the treatment room. However, if a source of radiation is implanted inside you, as occurs with internal radiation therapy, a number of safety measures are necessary.

While you are in the hospital and the implant is in place, women who are pregnant and children younger than 18 should not visit. Other visitors should sit at least 6 feet from your bed and limit their stay to 30 minutes or less each day. Permanent implants remain radioactive after a patient is discharged from the hospital, and he or she should refrain from close (less than 6 feet) or lengthy (more than 5 minutes) contact with women who are pregnant and children for two months.

If your treatment includes systemic (whole body) radiation therapy, safety precautions must be followed for the first few days after treatment. The risk of radiation exposure to family and friends can be minimized using the following precautions. Your health-care team will provide specific instructions on:

Personal hygiene following toilet use
Use of separate utensils and towels
The importance of drinking plenty of fluids to flush the remaining radioactive material from your body
Avoiding sexual contact
The necessity to minimize contact with infants, children, and women who are pregnant

More Information

Part II: Radiation Therapy—Your Personal Experience

Part III: Side Effects of Radiation Therapy

Frequently Asked Questions About Radiation Therapy

Additional resources

National Cancer Institute (NCI): Radiation Therapy for Cancer: Questions and Answers

The American Society for Therapeutic Radiology and Oncology (ASTRO)

Medline Plus: Radiation Therapy Introduction (tutorial)

American Cancer Society (ACS): Radiation Therapy Principles

ACS: Questions About Radiation Therapy

MayoClinic.com: Radiation therapy: Using high-powered x-rays to kill cancer cells

Kids Health: Radiation Therapy

Last Updated: July 19, 2005