Intensity modulated radiation therapyIntensity modulated radiation therapy (IMRT) is a powerful cancer-fighting technology. Annually, Mayo Clinic radiation oncologists treat more than 200 patients using IMRT.
Oncologists consider IMRT to be ideal for prostate cancer as well as benign and malignant tumors of the head and neck, and other organs that lie near important body parts such as the eyes, optic nerves, brain, brain stem, salivary glands, bladder, rectum, small bowel, kidneys, liver, lung and spinal cord.
Conditions Treated with IMRT
Advantages of IMRT
The advantages of IMRT, compared to traditional radiation therapies,
include : -
- Decreased radiation to normal sensitive surrounding tissue
- Decreased chance of harming normal cells
- Higher radiation dosage to cancer cells
- Precise radiation distribution
- Increased chance of destroying cancer cells
How It Works ?
A more standard radiation therapy called three-dimensional conformal radiation therapy (3-D CRT) uses digital diagnostic imaging, computers and special software to conform the radiation beam to the shape of the tumor. IMRT is the latest advance in 3-D CRT technology. IMRT involves the use of varying intensities of hundreds of small radiation beams to produce dosage distributions that are more precise (conformal) than those possible with 3-D CRT.
In intensity modulated radiation therapy (IMRT), very small beams, or beamlets, are aimed at a tumor from many angles. During treatment, the radiation intensity of each beamlet is controlled, and the beam shape changes hundreds of times during each treatment. As a result, the radiation dose bends around important healthy tissues in a way that is impossible with other techniques. Because of the complexity of these motions, physicians use special high-speed computers, treatment-planning software, diagnostic imaging and patient-positioning devices to plan treatments and control the radiation dose during therapy.
For IMRT to be effective, the anatomical position of the tumor and surrounding healthy tissues must be accurately defined. Computed tomography (CT), positron emission tomography (PET) and magnetic resonance (MR) imaging provide the necessary three-dimensional anatomical information. It's also important to accurately position and immobilize the patient during treatment.
This may be done with special head frames (if the head or brain is being treated), or with advanced imaging devices such as electronic portal imaging and scanning ultrasound, which provide daily information about the location of internal organs. Some organs, such as the prostate, move due to normal daily volume changes in the bladder and rectum. Gold seeds may be placed into the prostate to track prostate movement daily and ensure more precise targeting.
A device called a multileaf collimator adjusts the size and shape of the computer-determined radiation beams. The collimator, a computer-controlled mechanical device, consists of up to 120 individually adjusted metal leaves. These leaves move across the irradiated tissue while the beam is on, blocking out some areas and filtering others to vary the beam intensity and precisely distribute the radiation dosage.
Radiation oncologists usually administer a regimen of IMRT treatments over four to eight weeks. The total dose of radiation and the number of treatments given depend on the size, location and type of cancer; the patient's general health; and other medical therapy the patient is receiving.
IMRT permits the delivery of a high dose of radiation to the cancer while minimizing dose to other sensitive organs. Here multiple beams are all focused on the prostate. Each of these beams has a number of sub-beams or segments, and the intensity of each segment is varied according to the treatment plan.
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