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Q: How does radiation therapy work?
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A: Cancer cells grow and divide more rapidly than many of the normal cells around
them. High doses of radiation can kill cells or keep them from growing and dividing,
and it has proven to be particularly effective in killing cancer cells and shrinking
tumors. Although some normal cells are affected by radiation, most normal cells
recover more fully from the effects of radiation than do cancer cells. Doctors
carefully limit the intensity of treatments and the area being treated so that the
cancer will be affected more than normal tissue.
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Q: What is IMRT (Intensity Modulated Radiation Therapy)?
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A: IMRT involves varying (or modulating) the intensity of the radiation (in this case, X-rays), being used as therapy for cancer. It is a new form of radiation therapy that uses computer-generated images to plan and then deliver more tightly focused radiation beams to cancerous tumors than is possible with conventional radiotherapy. With this capability, clinicians can deliver a precise radiation dose that conforms to the shape of the tumor, while significantly reducing the amount of radiation to surrounding healthy tissues. Consequently, the technique can increase the rate of tumor control while significantly reducing adverse side effects.
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Q: Why would I want to be treated with IMRT?
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A: IMRT is the most precise form of radiation therapy available. It allows physicians to escalate the radiation dose to cancer cells, and in some cases, even more precisely to specific metabolically active regions within a tumor, while keeping the dose to surrounding tissues as low as possible.
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Q: What kind of radiation is used in IMRT?
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A: Currently, photons (X-rays) are used to deliver IMRT. The radiation is generated by a machine called a linear accelerator. This machine stands approximately nine feet tall, is nearly 15 feet long and can be rotated around the patient with great precision. Operationally, microwave energy, similar to that used in satellite television transmission, is used to accelerate electrons to nearly the speed of light. As they reach maximum speed they collide with a tungsten target, which in turn releases photons, or X-rays. Very small beams with varying intensities can be aimed at a tumor from various angles to attack the target in a complete three-dimensional manner. In fact, IMRT can be delivered with beams the size of 2.5 x 5-millimeter pixels – the size of a pencil tip – each with varying intensity. The idea is to deliver the lowest dose possible to the surrounding tissue, reducing the chance of causing a radiation side effect, while still delivering the maximum dose to the tumor.
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Q: Does radiation therapy expose people to radioactive substances?
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A: Many people, when they hear the word "radiation," think immediately of radioactive substances. However, no radioactive substances are involved in the creation of X-rays or electrons by a linear accelerator. When a linear accelerator is switched "on," radiation is produced and aimed directly at cancer cells. Then, like a flashlight, when the machine is switched off, there is no more radiation - none is "stored" or "transported."
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Q: What happens when a person is treated with IMRT?
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A: IMRT treatment involves four basic steps: diagnosis, simulation, treatment planning and delivery. As part of diagnosis, physicians generate three-dimensional diagnostic images (usually CT or MRI) of the patient's anatomy and use these to specify the dose of radiation each area will receive. In all cases, treatment planning includes a simulation session to further localize the cancer and finalize the radiation treatment plan. Patients receive the IMRT treatment according to various schedules, usually five days a week for six or seven weeks. Each treatment takes ten to fifteen minutes.
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Q: How long is a course of IMRT treatment?
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A: Radiation therapy usually is given five days a week for six or seven weeks. When radiation is used for palliative care, the course of treatment lasts for two to three weeks. For each radiation therapy session, the patient is in the treatment room for about 15 to 30 minutes. These types of schedules, which use small amounts of daily radiation rather than a few large doses, help protect normal body tissues in the treatment area. Weekend rest breaks allow normal cells to recover. The total dose of radiation and the number of treatments a patient needs depend on the size and location of the cancer, the type of tumor, the patient's general health and other factors.
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Q: What are the effects of treatment?
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A: External radiation therapy does not cause a patient's body to become radioactive. Patients need not avoid being with other people because of treatment. Even hugging, kissing, or having sexual relations with others pose no risk to them of radiation exposure. Side effects of radiation therapy most often are related to the area that is being treated. Most side effects that occur during radiation therapy, although unpleasant, are not serious and can be controlled with medication or diet. They usually go away within a few weeks after treatment ends. With IMRT, some patients have no side effects at all.
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