Radiation Therapy

Radiation is a special kind of energy carried by waves or a stream of particles. When radiation is used at very high levels it can be used to treat cancer and other illnesses. High levels of radiation can kill cells or keep them from growing and dividing. Cancer cells grow and divide more rapidly than many of the normal cells around them and so are very vulnerable to radiation.

Radiation therapy is an effective way to treat many kinds of cancer in almost any part of the body. Very special techniques are used to make sure that cancer cells are destroyed by the radiation while healthy tissue is protected. About half of all people with cancer are treated with radiation.

Radiation therapy is given by an expert team, which includes physicists, dosimetrists, nurses and therapists. A physician called a radiation oncologist leads the team.

Equipment and Techniques

The CHEM Center specializes in external beam Radiation Therapy (also called Radiotherapy and Radiation Oncology). Radiotherapy is very dependent on specialized equipment and sophisticated computers to deliver therapy.

Linear Accelerator

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 1.5 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.

Superficial Treatment Unit

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, is 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.

CT Scanner

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.

3D Treatment Planning (conformal therapy)

Radiotherapy often involves aggressive treatment of tumors, which are difficult to identify or are located close to sensitive structures. In these cases, the Radiation Oncologists at the 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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