Intensity Modulated Radiation Therapy
Key Terms: Ionizing radiation.
Definition
Intensity modulated radiation therapy uses a computer to deliver precise, three-dimensional doses of x rays to a tumor to treat cancer.
Purpose
As a new and special form of radiation therapy, intensity modulated radiation therapy (IMRT) offers special treatment options for cancer patients. When a patient has cancer, he or she may have radiation therapy to destroy the tumor or cancerous cells. The radiation therapy may be the only treatment given or a treatment prescribed along with surgery and/or chemotherapy.
The radiation aimed at the cancerous cells also can destroy nearby healthy cells. IMRT is an advanced treatment method that allows physicians to target the cancer so effectively that healthy tissue receives little to no radiation, even when the tumor is wrapped around a vital organ. This makes IMRT a good choice for many cancer patients, particularly those with small tumors, brain and spinal cord tumors, prostate cancer, cancer of the head and neck, many children, infants with certain muscle tumors, and some patients who have previously received radiation treatments. Research continues on expanding use of IMRT for a number of cancers; clinical trials are underway around the world.
Precautions
Any time a patient is considered for radiation therapy, physicians weigh the risks and benefits of the procedure. IMRT, like any external radiation therapy procedure, introduces x rays (ionizing radiation) to the patient's skin, tissues, and organs near the treatment area. Some patients will not be candidates for treatment. IMRT will require frequent trips to the radiation oncology facility for the prescribed treatment plan and careful following of instructions to deal with radiation side effects. On the positive side, the accuracy of IMRT means some patients who may not have been candidates for radiation therapy under older, less precise methods now can have radiation treatment. IMRT can deliver radiation to the intended target more precisely and do a better job of sparing surrounding organs and tissues. The oncology treatment team should discuss all risks and benefits of IMRT with the patient.
Description
Physicians have used radiation to treat cancer for more than 100 years. The damaging effects of x rays can destroy cancerous cells in the body and help rid the patient of the pain or related spread and complications of some cancers. For some patients, radiation therapy is the first treatment physicians choose; for others the treatment is used after surgery or chemotherapy or at the same time as chemotherapy. Radiation therapy also sometimes is called "radiotherapy."
The goal of radiation therapy is to destroy as many cancer cells as possible, while limiting damage to nearby healthy tissue. To accomplish this, complicated dose measurements are made based on information gathered by studying the tumor before radiation treatment begins. Today, physicians can use procedures such as computed tomography (CT) to produce three-dimensional models that can better pinpoint the tumor. Planning radiation treatments in three dimensions allows physicians to target the radiation beams at the tumor's height, width, and depth. This newer technique is called "3-D conformal radiation therapy."
IMRT is a new type of 3-D conformal radiation therapy that uses beams of varying intensities. By doing so, the beams, which can strike the tumor from three dimensions, also can deliver different doses to small areas of tissue at once. This offers more individualized targeting of the tumor than in the past, so that the radiation oncologist (a physician who specializes in using radiation to treat cancer) can plan higher doses to the tumor and lower doses to the nearby tissue. Insurance companies have found IMRT a valuable treatment for many cancers in recent years because of its effectiveness.
Tomotherapy is a form of IMRT that delivers the radiation dose by rotating the beams over a small slice of tissue.
Most IMRT procedures are performed at a cancer center, radiation oncology physician office or outpatient facility, or in a hospital. The radiation oncologist oversees the patient's plan, working closely with a team of professionals. A medical physicist has special training in radiation physics and the operation and repair of radiology and radiation therapy equipment. The physicist also may help develop the patient's treatment plan. A medical dosimetrist works under the direction of the radiation oncologist and medical physicist to calculate radiation dose. IMRT treatments normally are performed by a radiation therapist, a specially trained technologist who positions the patient and runs the equipment. A radiation oncology nurse also may help with managing care, side effects, and explaining the treatments.
As the treatment begins, the patient is positioned on a treatment table in a precise location that has been set in treatment planning or simulation sessions. A special molding or other device may be applied to help keep the patient from moving during the procedure. The radiation therapist can observe the patient throughout the entire procedure through a window or closed circuit television. The therapist may reposition the patient during the procedure. A treatment session usually lasts about 15 to 30 minutes. The procedure should be painless, but if the patient is uncomfortable, the therapist can stop the machine. The number of treatments a patient must return for will depend on the type and stage of cancer. Some patients may receive treatments every day for a period of a several weeks.
Preparation
Before beginning IMRT treatment, the radiation oncologist and treatment team will need to know the precise location of the tumor in the body (anatomical position). This means the patient may have to go for several imaging studies in addition to those already completed to diagnose the cancer. Computed tomography (CT), positron emission tomography (PET) scans, and magnetic resonance imaging (MRI) may be used to provide three-dimensional information for the IMRT system. These imaging visits and the resulting work of the treatment team often are called treatment simulation. The patient also may have to go to the radiation therapy facility prior to treatment for a planning session. At this session, a special device may be molded to help the patient maintain an exact treatment position. The patient also may receive a mark or tattoo with colored ink to help align and target the equipment once treatment begins.
Aftercare
The radiation oncologist, radiation therapist, or radiation oncology nurse will provide instructions on IMRT aftercare. Since some effects of radiation therapy do not begin to show up until after several treatments, these instructions may vary throughout the course of treatment. Some side effects of radiation therapy occur soon after treatment begins, but others occur later. The most common side effects of external radiation therapy are fatigue and skin changes.
People undergoing radiation therapy who become fatigued may need to reduce their routines somewhat and not try to do too much. It is best to keep in touch with the treatment team for advice on feelings of fatigue and care for its effects. If skin becomes irritated, it also is important to follow the team's instructions concerning washing, sun exposure, and use of skin care products.
Risks
Radiation therapy carries the risk of radiation reaching and damaging normal tissues or organs near the area being targeted. However, IMRT treatment is more precise than other external radiation therapy procedures. There also is a small risk of dose being calculated incorrectly and a patient receiving too much radiation, but equipment should be run by FDA-approved software. Facilities have many quality processes in place to ensure the correct dose is given to the precise location on the correct patient. Radiation therapy also can cause low levels of white blood cells and platelets. White blood cells help fight infection and platelets help blood clot. Radiation therapy causes other side effects and risks, depending on the area being treated, though many only last a short time. For example, radiation treatment to the head can cause hair loss (alopecia), but the hair eventually will grow back.
Normal Results
After completion of IMRT treatments, cancer cells should stop dividing and growing, which should slow tumor growth. Often, cancer cells completely die and a tumor shrinks or disappears. With IMRT, there should be little radiation damage to the normal, healthy tissues around the tumor and fewer resulting side effects.
Questions to Ask Your Doctor
- How long will my treatment last: how many times will I have to come in?
- How experienced are you and your staff in providing IMRT?
- What are some of the side effects I can expect from IMRT?
- Are there signs I should watch for following treatment that are abnormal and require a call to you or your nurse?
Abnormal Results
The treatment may not always completely eliminate cancer cells. A cancer may still partially remain or recur at a later date. Physicians usually follow up with imaging studies to see how the treatment is progressing and set up a future schedule check for cancer recurrence.
Resources
Periodicals
"Beyond Conventional Radiation" RN (June 1998):34–38.
"IMRT and Image-guided Tumor Localization Improve Radiotherapy in Prostate Cancer." Health & Medicine Week (April 5, 2004):691.
"IMRT Reduces Radiation Dose to Healthy Breast Tissue." Cancer Weekly (Oct. 26, 2004):30.
Leaver, Dennis. "IMRT Part I." Radiation Therapist (Fall 2002):106–124.
"Study Finds IMRT Is Cost-effective Compared to Previous Conformal Technique." Medical Devices & Surgical Technology Week (Oct. 31, 2004):291.
Organizations
American Society for Therapeutic Radiology and Oncology. 12500 Fair Lakes Circle, Suite 375, Fairfax, VA 22033-3882. 800-962-7862. http://www.astro.org.
Other
External Radiation Therapy. Web page. American Cancer Society, 2004. http://www.cancer.org.
Intensity-modulated Radiation Therapy (IMRT). Web page. Radiological Society of North America, 2005. http://www.radiologyinfo.org.
—Teresa G. Odle
