Equipment and Techniques
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The CHEM Center specializes in external beam Radiation Therapy (also called Radiotherapy and Radiation Oncology). Radiotherapy is very dependant on specialized equipment and sophisticated computers to deliver therapy.
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Linear Accelerator
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The majority of Radiation Therapy is delivered by a Linear Accelerator. This is a very powerful machine capable of rapidly moving or accelerating electrons down a long (linear) tube. At the end of the tube, the electrons will strike a small target made of tungsten and their energy, measured in the millions of volts, is converted into x-rays. X-Rays are photons, just like visible light, only far more energetic. When the Linear Accelerator is used in this configuration, we say it is in Photon Mode.
The Linear Accelerator (or Linac as it is sometimes referred to) may also be used in Electron Mode. If the tungsten target were slid aside then the electrons would not be converted into x-rays and a Beam of Electrons would be emitted. An Electron Beam is another form of radiation and it behaves quite differently from Photons. Electrons are quite effective in treatment of shallow tumors, located from ½ to 3 inches from the skin surface.
The CHEM Center has 2 Linear Accelerators, one of which is designed to produce electrons as well. These Linacs are located in a special room sometimes called a vault.
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Superficial Treatment Unit
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CHEM is equipped with a Superficial Treatment Unit. This is a machine which produces x-rays which, while far more energetic than light or microwaves, are much LESS energetic that those produced by the Linac. While the x-rays produced by a Linac can be from a few up to 18 Million Electron Volts (MV) the x-ray beam produced by the superficial unit is ‘only’ a hundred thousand electron volts (100 KV). What this means to the Radiation oncologists is that the beam from this machine is perfectly suited for treating very shallow or Superficial tumors like those of many skin cancers.
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Simulator
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The Simulator is a diagnostic type x-ray unit capable of taking x-ray images (Films) or the area that the physician wishes to treat. A Simulator, however, is more than just an x-ray unit . The arm which supports the x-ray head, commonly called the Gantry, is engineered to very high rigidity and precision so that it will accurately mimic, or Simulate the rotational treatment geometry of the Linac.
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CT Scanner
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CHEM installed a Computed Tomography (CT) Scanner dedicated to the imaging of cancer patients for the purpose of precise targeting and treatment delivery. The CT Scanner is a computer controlled x-ray unit which rapidly rotates around the patient (inside it’s housing and out of view) to produce cross sectional images of great detail. Information such as that provided by the CT scanner is essential to the Radiation oncologist and the Physics staff for their goal of precise and efficacious treatment techniques. The CT scanner produces a series of cross sectional images which a special computer, called the Treatment Planning Computer can ‘stack up’ like a loaf of bread and reconstruct a 3 dimensional model of the patient.
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3D Treatment Planning (conformal therapy)
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Radiotherapy often involves aggressive treatment of tumors which are difficult to identify or are located close to sensitve structures. In these cases, the Radiation Oncologists at the CHEM Center will rely on 3 Dimensional (3-D) treatment planning. This advance enables the identification of a tumor on multiple CT scan "slices" and the reconstruction of the tumor in 3-D on a computer screen so that it may be viewed from any angle. Carefully angled beams can then be directed to the tumor while avoiding sensitive structures. With this tool, the physician can confidently design complex treatment schemes using many small beams to reliably irradiate the tumor.
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