System delivers radiation precisely to tumor
Intensity Modulated Radiation Therapy (IMRT) provides a precise radiation beam that conforms as closely as possible to the shape of the tumor. Rather than have a single large radiation beam pass through the body with uniform intensity, IMRT breaks the radiation into thousands of pencil-thin beams with varying intensity. The radiation beam itself is shaped by 120 computer-controlled mechanical “leaves” or “fingers” to match the shape of the tumor, and the result is a three-dimensional system providing radiation directed to tumor tissue. IMRT can be used to treat tumors that might have been considered untreatable in the past due to close proximity of vital organs and structures. Treating such tumors requires tremendous accuracy. For example, in the case of head and neck tumors, IMRT allows radiation to be delivered in a way that further minimizes exposure of the spinal cord, optic nerve, salivary glands or other important structures. In the case of prostate cancer, exposure of the nearby bladder or rectum may be minimized to a greater extent than with standard techniques. IMRT is being used to treat tumors in the breast, head and neck, liver, lung, pancreas, prostate and other cancers where precisely placed beams can be focused to carefully target tumor cells without harming surrounding healthy tissue. “Radiation therapy is used today in more than half of all cancer treatments because of its unique clinical advantages, and it is becoming steadily more effective with new technologies that permit ultra-precise dose delivery,” said Kenneth N. Vanek, Ph.D., an MUSC radiation physicist and associate chairman of the Department of Radiation Oncology. With IMRT, a powerful computer program optimizes a treatment plan based on a physician's dose instructions and information about tumor size, shape and location in the body. A medical linear accelerator is equipped with a special device called a multileaf collimator that shapes the radiation beam. This enables the delivery of the radiation in accordance with the treatment plan. The equipment can be rotated around the patient to send radiation beams from the most favorable angles for giving the tumor a high dose while preserving important healthy tissues. Clinical studies conducted at Memorial Sloan Kettering Cancer Center
in New York indicate that the higher dose rates delivered with IMRT techniques
significantly improved the rate of local tumor control. At the same time,
clinicians delivered these higher doses while simultaneously reducing the
rate of normal tissue complications from 10 percent to 2 percen.
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