Intensity Modulated Radiation Therapy (IMRT)
The goal of all radiation therapy is to irradiate a tumor with a lethal dose while limiting the radiation received by the normal tissue that surrounds a tumor. Methods used by doctors to accomplish this include shaping the radiation beam with the use of lead shields in the front or head of the linear accelerator and the angling of several beams of radiation to intersect at the targeted tumor. Both of these methods allow for normal tissues to be spared while at the same time delivering a higher dose of radiation to the tumor.
IMRT uses a complex system of shields inside the machine together with sophisticated dose calculation methods to use literally thousands of tiny beams, each individually shaped and coming from many different angles, to target the area to be irradiated. This dynamic beam is different from the static conformal treatment method.
IMRT is useful in treating small, fairly stationary targets surrounded by a large volume of normal tissue and/or critical structures that are especially close to the targeted tumor. Because these treatments focus on such a small area near critical structures, it is necessary to verify patient positioning and targeting of the beam on a daily basis. Daily verification is vital to ensure accuracy and takes only a few additional minutes before treatment begins. The total length of time a patient is in the treatment room is usually 15 to 30 minutes depending on the complexity of the treatment delivery. Types of tumors that may be treated with IMRT include prostate, brain, spinal cord, head and neck, and tumors very close to radiosensitive normal tissues such as the optic nerve.
Some tumors may be too mobile to be treated with IMRT. Your physician will discuss with you if IMRT is appropriate in your case.