Intensity Modulated Radiation Therapy
by Krisha McCoy, MS
Radiation therapy uses radiation to kill cancer cells and shrink tumors.
Intensity modulated radiation therapy (IMRT) uses radiation beams of different intensities. The beams deliver appropriate doses of radiation to the tumor and reduce the dose to nearby healthy tissue.
Reasons for Procedure
Radiation therapy works to destroy or shrink the tumor to eliminate or prevent the spread of cancer. It can also be used to relieve symptoms caused by the tumor, such as pain and bleeding. Compared with conventional radiation therapy, IMRT can safely deliver greater doses of radiation. The higher dose may also improve the success of the treatment.
Some normal cells will be damaged with radiation. The goal of radiation therapy is to kill as many cancer cells as possible while limiting damage to healthy cells.
IMRT is generally associated with fewer side effects than conventional radiation therapy. Side effects vary from person to person, depending on the location of your cancer. Some people experience no side effects at all. General side effects of radiation therapy may include:
Although uncomfortable, the side effects associated with radiation therapy are usually not serious. They can be controlled with medication and diet. Your radiation oncologist can explain the side effects you are likely to experience and help determine the best strategies to manage them.
What to Expect
Prior to Procedure
Planning for IMRT is complex and generally takes 2-5 days. Planning may include:
Description of the Procedure
Using the marks made on your skin as a guide, the radiation therapist will position you on the treatment table. CT or MRI scans may be used to check the accuracy of the treatment setup. The therapist leaves the room to control the movements of the radiation machine. The treatment delivers radiation in a 3-dimensional manner. This will help to conform as closely as possible to the shape of the tumor. The healthy tissue receives smaller doses of radiation than the tumor.
You will be asked to remain still during the radiation treatment. You may breathe normally. In general, you will not feel or sense anything during treatment. However, the machine can be stopped if you feel sick or uncomfortable. The therapists will be observing you with a monitor. You will be able to communicate to them should you need to.
Immediately After Procedure
You will be able to leave and resume your normal daily activities. Receiving IMRT does not make you radioactive. You do not need to avoid being around other people because of the treatment.
How Long Will It Take?
Each session will take 15-30 minutes. Patients are typically scheduled for IMRT 5 days per week for 4-8 weeks.
How Much Will It Hurt?
Holding one position may become a little uncomfortable, but it is not painful.
During treatment, your doctor will want to see you at least once a week. You may have blood tests or other studies performed.
After your treatment is completed, you will come in for regular visits to monitor for side effects and healing and check for signs of recurrent disease. You may require further testing, medication, or rehabilitative treatment.
Call Your Doctor
Call your doctor if any of these occur:
If you think you have an emergency, call for emergency medical services right away.
American Cancer Society
Radiology Info—Radiological Society of North America
Canadian Association of Radiologists
Canadian Cancer Society
IMRT. International Radiosurgery Support Association website. Available at:
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Accessed January 28, 2021.
Intensity-modulated radiation therapy (IMRT). Radiological Society of North America Radiology Info website. Available at: https://www.radiologyinfo.org/en/info.cfm?pg=imrt. Accessed January 28, 2021.
Radiation therapy. American Cancer Society website. Available at: https://www.cancer.org/treatment/treatments-and-side-effects/treatment-types/radiation.html. Accessed January 28, 2021.
Radiation therapy and you: Support for people with cancer. National Cancer Institute website. Available at: https://www.cancer.gov/publications/patient-education/radiation-therapy-and-you. Accessed January 28, 2021.
Radiation therapy for cancer. National Cancer Institute website. Available at: https://www.cancer.gov/about-cancer/treatment/types/radiation-therapy/radiation-fact-sheet. Accessed January 28, 2021.
Last reviewed December 2020 by EBSCO Medical Review Board Mohei Abouzied, MD, FACP
Last Updated: 1/28/2021
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