The most common machine used to distribute external beam radiotherapy treatment is known as a linear accelerator or LINAC for short. LINAC systems generate high energy x-rays that are carefully aimed at the cancerous tumors. This process is done with much care given to direct the rays in a manner that does as little harm as possible to the healthy tissue surrounding the tumor. Linear accelerators are used to treat cancerous tumors on all areas of the body.
Some LINAC systems that are more advanced have the capability to deliver radiation on or near the surface of the skin. In this type of treatment electrons are used in replacement of high energy x-rays.
Newer linear accelerators have the ability to deliver radiation using Intensity Modulated Radiation Therapy, IMRT. These systems use multi-leaf collimators adjust the shape of the radiation beam to match the shape of the tumor. Without these adjustments LINAC systems would only be able to shoot radiation beams in the shape of a square or rectangle.
Radiographers all have different methods that they use to make sure the radiation treatment is targeting the exact location of the cancerous tumor. In its most fundamental form radiation is just a plain x-ray. Most linear accelerators work through digital imaging where the bottom arm of the machine takes an EPI, electronic portal image, or PI, portal image.
The image is compared by radiographers, to images that were generated during the planning process of your treatment as a type of checks and balances before treatment is delivered. The quantity of images that are taken to compare between depends on the departments protocol for imaging. Different types of radiotherapy treatment machines have an On-Board Imager, OBI, that is comprised of a Kv x-ray and detector. Higher quality images are obtained as a verification which allows for another radiotherapy technique known as Image Guided Radiotherapy, IGRT. With IGRT the accuracy of treatment is improved as daily changes are accounted for such as changes in organ location which can in turn reduce unpleasant side effects.
Electrons are generated and speed up to almost as close to the speed of light using electrical fields. The energy continues to increase until it collides with its intended target and then releases the photon energy. These photons enter the patient in an attempt to break down the DNA cells in the cancerous tumor. Healthy cells are most often able to mend themselves where as the cancerous tumors don’t and eventually die.
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