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What is Intensity Modulated Radiation Therapy (IMRT)?

Dr. Joseph Simpson treats patients at

Christian Hospital
11155 Dunn Road, Suite 101E
St. Louis, MO 63136
 
Phone:  314-653-5255     Fax: 314-653-4283

Siteman Cancer Center
Center for Advanced Medicine
4921 Parkview Place, LL
St. Louis, MO 63110
 
Phone:  314-747-7236     Fax: 314-362-7769
______________________________________

Question:  My doctor is sending me to radiation oncology for IMRT. What exactly is that?

Answer:  IMRT stands for intensity modulated radiation therapy. It is an advanced form of conformal radiation therapy and requires complex treatment planning and dose delivery. Not all hospitals offer IMRT and not all radiation oncologists are trained to use it.

The goal of radiation therapy is to send the greatest amount of radiation to destroy the tumor cells, without harming healthy tissue nearby. Tumors are three dimensional. The benefit of IMRT is that the variation in the intensity of the multiple radiation fields aimed at the tumor, allows for greater conformality (matching) of the dose to the actual shape of the tumor inside the patient. IMRT utilizes beams with multileaf collimators that can be turned on or off or be blocked during treatment, varying the radiation beam intensity across the targeted field.

Therefore, IMRT is particularly suited to cover irregular tumor shapes completely and spare nearby normal tissues. Patients with tumors first undergo a CT-simulation scan – a painless procedure that maps the exact shape of the tumor. In planning the treatment, the radiation oncologist must outline, on each slice of the CT scan obtained for simulation, the specific tumor targets and normal tissues at risk.
 
Patients, whose treatment with irradiation would otherwise result in large amounts of normal tissue exposure, can be treated with IMRT with much less exposure of nearby normal tissues to high doses of radiation and the risk of late radiation damage.
 
As examples, IMRT is widely used to spare the salivary glands when treating head and neck cancers, the brain stem, optic chiasm and optic nerves in brain tumor treatment, the rectum and bladder in prostate cancer treatment, and the small bowel and kidneys in pancreatic tumor treatment.
 
In left-sided breast cancer treatment IMRT can minimize the heart dose, helping to avoid increasing the risk of later coronary artery disease. It also is a method that can be adapted in specialized programs to stereotactically treat certain sized lung and liver tumors. In summary, IMRT is currently the best radiation technique available for treating many cancer patients.
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Copyright 2013 Washington University School of Medicine