This page was reviewed under our medical and editorial policy by
Bertram Yuh, MD, MISM, MSHCPM, Urologic Surgeon, City of Hope | Duarte.
This page was reviewed on August 17, 2023.
Intensity-modulated radiation therapy, or IMRT, may be recommended following cancer diagnosis as part of the patient's treatment regimen.
IMRT is a type of advanced external beam radiation therapy (EBRT) delivered in different amounts from varying angles during treatment. This allows higher doses of radiation therapy to target cancerous cells and reduces the effect of radiation on healthy tissues surrounding the tumor.
Real-time three-dimensional (3D) images guide the IMRT process, providing precise information on the location of cancerous cells and healthy cells in the path of the radiation beam. IMRT is a type of 3D conformal radiotherapy, meaning it uses computer images from computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) scans.
These images show the care team the exact size and shape of the tumor, as well as the healthy tissue nearby. The scans help plan the direction, angles and dose strength of radiation treatment.
Unlike traditional 3D conformal radiation, IMRT uses more and smaller radiation beams. The strength of each radiation beam can be rapidly changed during treatment to give higher amounts to cancerous areas and lower amounts to healthy areas during the treatment as the machine moves around the patient. This may allow for less damage to the healthy tissue near the cancer.
IMRT is a common type of radiation therapy. Because the treatment can be planned so precisely, with different levels of radiation given at different angles depending on the target tissue (cancerous or healthy), it’s especially used to treat head and neck cancers—such as oropharyngeal cancer, nasopharyngeal cancer or laryngeal cancer—where key organs and tissues are more condensed. It’s also commonly used as the radiation treatment for prostate cancer.
A key part of IMRT is having image scans so the care team can learn as much as possible about the size and shape of the patient's tumor.
Before treatment, the patient may hear the care team refer to inverse planning, which is how IMRT treatment is planned. First, the care team determines the ideal dose of radiation. From there, the team uses the patient's scans to plan for the cancerous cells to get the ideal dose, while healthy tissue nearby receives lower doses. Because the care team first determines the ideal dose and then outline the different strengths at different angles—which is the opposite of more traditional radiation treatment planning—it’s called inverse planning.
While the patient and his or her care team are in the treatment planning process, it's important to ask any questions about the treatment or what to expect. The patient may consider asking:
During the time the patient is receiving IMRT, he or she works with a radiation oncologist who plans and oversees treatment. This specialist meets with the patient before treatment starts to review the patient's medical history and any recent test results.
A radiation therapist delivers the treatment and ensures the patient is in the right position each time. Because radiation therapy treatments need to be very precise, the therapist may mark the patient's body with dots of ink that remain through all the IMRT sessions.
Though simulation scans are typically done to help plan treatment, the care team may also use real-time images during the IMRT procedure to guide the treatment and intensity.
The care team may indicate how often the patient needs to undergo IMRT and for how long. Most people receive treatment once a day, five times per week, for about five to eight weeks. The patient's treatment schedule will depend on the size, shape and type of cancer, as well as the patient's general health and any other cancer treatments he or she is receiving. IMRT is usually performed at an outpatient treatment center or as an outpatient treatment at a hospital.
Possible radiation therapy side effects tend to depend on the area of the body getting treatment. Some common side effects may include:
Ask the care team about possible side effects or risks associated with IMRT treatment and how to manage them.
IMRT is designed to reduce damage to healthy tissue during radiation therapy treatment by using higher doses directed at the tumor itself and lower doses when the beam is closer to healthy tissue. This is an especially important benefit for patients with head and neck cancers in avoiding tissue of important nearby structures such as the eyes, optic nerve, tongue or brain.
IMRT is also associated with a higher quality of life after treatment—again, especially when it comes to head and neck cancers, where the side effects of radiation treatment often affect the patient’s ability to eat and drink. Patients with head and neck cancers who undergo IMRT have reported fewer instances of dry mouth and better experiences with swallowing, allowing them to return to more normal eating and drinking habits after treatment.