Intensity Modulated Radiation Therapy

Radiation Oncology—
Intensity Modulated Radiation Therapy

What is Radiation Therapy?

Radiation therapy, sometimes called radiotherapy or irradiation, is the use of various forms of radiation to safely and effectively treat cancer and other diseases. Radiation oncologists may use radiation therapy to try to cure cancer, to control the growth of the cancer or to relieve symptoms, such as pain.

Radiation therapy works by damaging the DNA within cancer cells and destroying the ability of the cancer cells to reproduce. When these damaged cancer cells die, the body naturally eliminates them. Normal cells are also affected by radiation, but they are able to repair themselves in a way that cancer cells cannot.

Sometimes radiation therapy is the only treatment a patient needs, and other times it is only one part of a patientís treatment. For example, prostate and larynx cancer are often treated with radiation alone, but a woman with breast cancer may be treated with surgery, radiation therapy and chemotherapy.

Sometimes radiation therapy is used as adjuvant therapy to make your primary treatment more effective. For example, you can be treated with radiation therapy (the adjuvant treatment) before surgery (the primary treatment) to help shrink the cancer and allow less radical surgery than would otherwise be required, or you may be treated with radiation after surgery to destroy microscopic cells that may have been left behind.

A radiation oncologist may choose to use radiation therapy in a number of different ways. Sometimes the goal is to cure the cancer. In this case, radiation therapy may be used to:

Destroy tumors that have not spread to other parts of your body.
Reduce the risk that cancer will return after you undergo surgery or chemotherapy by killing tiny cancer cells that may remain.

In other cases, the goal is to reduce the symptoms caused by growing tumors and to improve your quality of life. When radiation therapy is administered for this purpose, it is called palliative care or palliation. In this instance, radiation may be used to:

Shrink tumors that are interfering with your quality of life, such as a lung tumor that is causing shortness of breath.
Alleviate pain by reducing the size of your tumor.

Is Radiation Therapy Safe?

Some patients have concerns about the safety of radiation therapy. Radiation has been used successfully to treat patients for more than a century, and in that time, many advances have been made to ensure that radiation therapy is safe and effective.

Before you begin treatment, your radiation oncology team will carefully tailor the treatment plan to make sure that you receive safe and accurate treatment. Throughout your treatment, members of your team check and re-check your plan. Sophisticated computers are also used to monitor and double-check the treatment machines to make sure that the proper treatment is given.

If you undergo external beam radiation treatment, you will not be radioactive following treatment because the radiation does not stay in your body. However, if you undergo brachytherapy, tiny radioactive sources will be implanted inside your body, in the tumor or in the tissue surrounding the tumor, either temporarily or permanently. Your radiation oncologist will explain any special precautions that you or your family and friends may need to take.

What Are the Different Kinds of Radiation?
The goal of radiation therapy is to get a high enough dose of radiation into the body to kill the cancer cells while sparing the surrounding healthy tissue from damage. Several different radiation therapy techniques have been developed to accomplish this. Depending on the location, size and type of your tumor or tumors, you may receive one or a combination of these techniques. Your cancer treatment team will work with you to determine which treatment and how much radiation is best for you.

Radiation therapy can be delivered in two ways, externally and internally. During external beam radiation therapy, the radiation oncology team uses a machine to direct high-energy rays at the cancer. Internal radiation therapy, also called brachytherapy, involves placing radioactive sources (for example, radioactive seeds) inside the patient.

External Beam Radiation Therapy

During external beam radiation therapy, a beam of radiation is directed through the skin to a tumor and the immediate surrounding area in order to destroy the main tumor and any nearby cancer cells. To minimize side effects, the treatments are typically given every day for a number of weeks.

The radiation beam comes from a machine located outside of your body that does not touch your skin or the tumor. Receiving external beam radiation is similar to having an X-ray taken. It is a painless, bloodless procedure. The most common type of machine used to deliver external beam radiation therapy is called a linear accelerator, sometimes called a “linac.” It produces a beam of high-energy X-rays or electrons.

At St. Agnes Cancer Center you may be treated with either:

Elekta Precise Linear Accelerator
Tomotherapy

Using sophisticated treatment planning software, your radiation oncology treatment team plans the size and shape of the beam, as well as how it is directed at your body, to effectively treat your tumor while sparing the normal tissue surrounding the cancer cells.

Several special types of external beam therapy are discussed in the following sections. These are used for particular types of cancer, and your radiation oncologist will recommend one of these treatments if he or she believes it will help you.

Three-Dimensional Conformal Radiation Therapy (3D-CRT)

Tumors usually have an irregular shape. Three-dimensional conformal radiation therapy, or 3D-CRT, uses sophisticated computers and computer assisted tomography scans (CT or CAT scans) and/or magnetic resonance imaging scans (MR or MRI scans) to create detailed, three-dimensional representations of the tumor and surrounding organs. Your radiation oncologist can then shape the radiation beams exactly to the size and shape of your tumor.

The tools used to shape the radiation beams are multileaf collimators or blocks. Because the radiation beams are very precisely directed, nearby normal tissue receives less radiation exposure.

Intensity Modulated Radiation Therapy (IMRT)

Intensity modulated radiation therapy, or IMRT, is a specialized form of 3D-CRT that allows radiation to be more exactly shaped to fit your tumor. With IMRT, the radiation beam can be broken up into many ìbeamlets,î and the intensity of each beamlet can be adjusted individually. Using IMRT, it may be possible to further limit the exact amount of radiation that is received by normal tissues that are near the tumor. In some situations, this may also allow a higher dose of radiation to be delivered to the tumor, increasing the chance of a cure.

Stereotactic Radiotherapy

Stereotactic radiotherapy is a technique that allows your radiation oncologist to precisely focus beams of radiation to destroy certain types of tumors. Since the beam is so precise, your radiation oncologist may be able to spare more normal tissue than with conventional external beam therapy. This additional precision is achieved through rigid immobilization, such as with a head frame as is used in the treatment of brain tumors. Although often performed in a single treatment, fractionated radiotherapy, where patients receive up to five treatments, is sometimes necessary.

Radiotherapy may be the only treatment if a very small area is affected. In addition to treating tumors, it can also be used to treat malformations in the brainís blood vessels and certain noncancerous (benign) brain tumors. Find out more about Stereotactic Radiosurgery.

Brachytherapy

Also known as internal radiation, brachytherapy involves placing radioactive material into a tumor or its surrounding tissue. Because the radiation sources are placed so close to the tumor, your doctors can deliver a large dose of radiation directly to the cancer cells with minimal exposure to normal tissue.

The radioactive sources used in brachytherapy, such as thin wires, ribbons, capsules or seeds, come in small sealed containers. Some sources are placed permanently and are referred to as implants. These radioactive sources remain in the body after their radiation has been expended and the source is no longer radioactive. Other sources are placed temporarily inside the body, and the radioactive sources are removed after the prescribed dose of radiation has been delivered.

Other Treatment Options

Systemic Radiation Therapy

Using radioactive isotopes to treat certain cancers is called systemic radiation therapy. The radioactive isotopes may be swallowed, given intravenously or injected into the body. For example, radioactive iodine (I-131) capsules are given to patients to treat some types of thyroid cancer. Another example is the use of intravenous radioactive samarium or strontium to treat pain due to cancer that has spread to the bone.

Radioimmunotherapy

Recent research has focused on the use of radioactive monoclonal antibodies, also called radiolabeled antibodies, to deliver doses of radiation directly to a tumor. This process is known as radioimmunotherapy. Antibodies are made by the body in response to the presence of antigens (substances recognized as foreign by the immune system).

Large quantities of particular types of antibodies, called monoclonal antibodies, can be made in the laboratory. These monoclonal antibodies can be attached to radioactive isotopes in a process called radiolabeling. When injected into the body, the radiolabled antibodies circulate in the bloodstream until they locate and bind to the surface of cancer cells. The cancer cells are then destroyed by the radiation carried in the antibody.

Radiosensitizers and Radioprotectors

Two types of drugs are being studied for their effect on cells undergoing radiation. One type includes drugs designed to make tumors more sensitive to radiation. It is hoped that these radiosensitizers will help radiation better destroy tumors. Other types of drugs are being evaluated to better protect the normal tissues near the area being treated.

These are called radioprotectors. An example of a radioprotector is a drug designed for head and neck cancer patients that helps decrease soreness some patients may feel during treatment and the dryness some patients may experience after treatment is completed.

Are There Any Side Effects?
Patients often experience little or no side effects from the radiation therapy and are able to continue their normal routines. However, some patients do feel some discomfort from the treatment. Be sure to talk to a member of your radiation oncology treatment team about any problems you may have.

Many of the side effects of radiation therapy are related to the area that is being treated. For example, a breast cancer patient may notice skin irritation, like a mild to moderate sunburn, while a patient with cancer in the mouth may have soreness when swallowing. These side effects are usually temporary and can be treated by your doctor or other members of the treatment team.

Side effects usually begin by the second or third week of treatment, and they may last for several weeks after the final radiation treatment. In rare instances, serious side effects develop after radiation therapy is finished. Your radiation oncologist and radiation oncology nurse are the best people to advise you about the side effects you may experience. Talk with them about any side effects you are having. They can give you information about how to manage them and may prescribe medicines that can help relieve your symptoms.

The side effect most often reported by patients receiving radiation is fatigue. The fatigue patients experience is usually not very severe, and patients can often continue all or some of their normal daily activities with a reduced schedule. Many patients continue to work full time during radiation therapy.

Many patients are concerned that radiation therapy will cause another cancer. In fact, the risk of developing a second tumor because of radiation therapy is very low. For many patients, radiation therapy can cure your cancer. This benefit far outweighs the very small risk that the treatment could cause a later cancer. If you smoke, the most important thing you can do to reduce your risk of a second cancer is quit smoking.