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Basic Information about understanding radiation therapy

Read the NCI booklet or NCI Fact Sheet on radiation, the ACS site,
or the ACS on basic principals, or Medline_plus, Cancer Network on radiation here
and the Oncolink page and see movie here

For information about what to expect the first day (called the simulation) go here.

Good Resource Sites for Basic Information about Radiation and   Radiation Therapy

EPA Site, Harvard, MD Anderson, NRC Site, RSNACancer Links,


What Is Radiation Therapy?

Radiation therapy (sometimes called radiotherapy, x-ray therapy, or irradiation) is the treatment of disease using penetrating beams of high energy waves or streams of particles called radiation. The radiation used for cancer treatment comes from special machines or from radioactive substances. Radiation therapy equipment aims specific amounts of the radiation at tumors or areas of the body where there is disease.

How Does Radiation Therapy Work?

Radiation in high doses kills cells or keeps them from growing and dividing. Because cancer cells grow and divide more rapidly than most of the normal cells around them, radiation therapy can successfully treat many kinds of cancer. Normal cells are also affected by radiation but, unlike cancer cells, most of them recover from the effects of radiation. To protect normal cells, doctors carefully limit the doses of radiation and spread the treatment out over time. They also shield as much normal tissue as possible while they aim the radiation at the site of the cancer.

What Are the Goals and Benefits of Radiation Therapy?

The goal of radiation therapy is to kill the cancer cells with as little risk as possible to normal cells. Radiation therapy can be used to treat many kinds of cancer in almost any part of the body. In fact, more than half of all people with cancer are treated with some form of radiation. For many cancer patients, radiation is the only kind of treatment they need. Thousands of people who have had radiation therapy alone or in combination with other types of cancer treatment are free of cancer. Radiation treatment, like surgery, is a local treatment — it affects the cancer cells only in a specific area of the body. Sometimes doctors add radiation therapy to treatments that reach all parts of the body (systemic treatment) such as chemotherapy, or biological therapy to improve treatment results. You may hear your doctor use the term, adjuvant therapy , for a treatment that is added to, and given after, the primary therapy.

Radiation therapy is often used with surgery to treat cancer. Doctors may use radiation before surgery to shrink a tumor. This makes it easier to remove the cancerous tissue and may allow the surgeon to perform less radical surgery.

Radiation therapy may be used after surgery to stop the growth of cancer cells that may remain. Your doctor may choose to use radiation therapy and surgery at the same time. This procedure, known as intraoperative radiation, is explained more fully in the "External Radiation Therapy section." 

In some cases, instead of surgery, doctors use radiation along with anticancer drugs (chemotherapy) to destroy the cancer. Radiation may be given before, during, or after chemotherapy. Doctors carefully tailor this combination treatment to each patient's needs depending on the type of cancer, its location, and its size. The purpose of radiation treatment before or during chemotherapy is to make the tumor smaller and thus improve the effectiveness of the anticancer drugs. Doctors sometimes recommend that a patient complete chemotherapy and then have radiation treatment to kill any cancer cells that might remain. When curing the cancer is not possible, radiation therapy can be used to shrink tumors and reduce pressure, pain, and other symptoms of cancer. This is called palliative care or palliation. Many cancer patients find that they have a better quality of life when radiation is used for this purpose.

What Are the Risks of Radiation Therapy?

The brief high doses of radiation that damage or destroy cancer cells can also injure or kill normal cells. These effects of radiation on normal cells cause treatment side effects. Most side effects of radiation treatment are well known and, with the help of your doctor and nurse, easily treated. The side effects of radiation therapy and what to do about them are discussed in the Managing Side Effects section. The risk of side effects is usually less than the benefit of killing cancer cells. Your doctor will not advise you to have any treatment unless the benefits -- control of disease and relief from symptoms -- are greater than the known risks.

How Is Radiation Therapy Given?

Radiation therapy can be given in one of two ways: external or internal. Some patients have both, one after the other.

Most people who receive radiation therapy for cancer have external radiation . It is usually given during outpatient visits to a hospital or treatment center. In external radiation therapy, a machine directs the high-energy rays at the cancer and a small margin of normal tissue surrounding it. The various machines used for external radiation work in slightly different ways. Some are better for treating cancers near the skin surface; others work best on cancers deeper in the body. The most common type of machine used for radiation therapy is called a linear accelerator . Some radiation machines use a variety of radioactive substances (such as cobalt-60, for example) as the source of high-energy rays. Your doctor decides which type of radiation therapy machine is best for you. You will find more information about external radiation in the next chapter.

When internal radiation therapy is used, the radiation source is placed inside the body. This method of radiation treatment is called brachytherapy or implant therapy. The source of the radiation (such as radioactive iodine, for example) sealed in a small holder is called an implant . Implants may be thin wires, plastic tubes (catheters), capsules, or seeds. An implant may be placed directly into a tumor or inserted into a body cavity. Sometimes, after a tumor has been removed by surgery, the implant is placed in the 'tumor bed' (the area from which the tumor was removed) to kill any tumor cells that may remain.

Another type of internal radiation therapy uses unsealed radioactive materials which may be taken by mouth or injected into the body. If you have this type of treatment, you may need to stay in the hospital for several days.