A multileaf collimator (MLC) is a medical device used to shape a beam of radiation for precise targeting of tumors while avoiding healthy tissue. It consists of collimators, tungsten shields, and position sensors, with computer software used to control movements and ensure safety.
A multileaf collimator (MLC) is a medical machine used to adjust a beam of radiation in the shape of a tumor or other abnormality. Connected to a linear accelerator, the machine is made up of collimators, or mobile jaws, which shape the radiation field. Sets of shields called leaves, made of tungsten metal, act as blocks to focus the beam into the desired shape. The device also comes in the form of a multi-leaf micro collimator (mMLC), suitable for treating irregularities approximately three inches (about eight centimeters) in diameter. It also has a slightly smaller leaf diameter than the full-sized system; computers are used in both types to sense and control the position of the sashes.
Parts of the multifoil collimator include a leaf control system, the mechanics that position the leaves, and position sensors. A video-optical system can be installed to visually show the position of each sash on a computer screen. Position sensing is also supported by limit switches and linear encoders, while linear motion systems are used in conjunction with motors for precise positioning of the leaves. Calibration is required for accurate readings between leaf positions and the signals generated by the positioning equipment.
Multi-leaf collimators can be particularly useful because they help focus radiation on tumors, at the exact dosage needed. They form a beam of radiation and control the dose so that healthy tissue, such as that in the lungs, spinal cord or eyes, is not affected. In targeting a specific area, a multifoil collimator can send multiple beams of radiation to a site so that the intensity does not cause damage to healthy parts of the body. Radiation detectors are also included in the machine; in the case of mMLC, a specific type of film is used to measure the dose, how the radiation is transmitted, and whether it is leaking.
The mechanical operation of a multileaf collimator is complex, with motion of the different components controlled in different axes. An operator uses computer software to monitor the position of each part and to control the precise movements that are required. The software also provides a graphical representation of the radiation field, so the operator knows exactly where the radiation is and can adhere to the machine manufacturer’s safety guidelines. All the functions of the machine, and the common configurations, can be controlled according to the exact conformation of the area to be treated.
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