What is a collimator? The collimator is another alias for the beam beam. “It is composed of two pairs of upper and lower rectangular collimators that can be opened and closed, commonly known as upper and lower diaphragms. The material is made of tungsten, lead or depleted uranium. The opening and closing movements of the upper and lower pairs of rectangular collimators can form square or rectangular radiation. wild.
According to the symmetry of the opening and closing movement, the collimator is divided into:
a. Symmetrical collimator system The upper and lower rectangular collimators of the system both make symmetrical opening and closing movements. In order to reduce the X-ray scattering on the side wall of the collimator and the penumbra of the edge of the collimator, the inner side of the rectangular collimator should be tangent to the direction of radiation. The thickness of the rectangular collimator should be thick enough to ensure that the x-ray transmission through the collimator meets national standards. The transmission amount should be less than 0.5% of the central ray intensity.
b. In clinical applications of the asymmetric collimation system, with the expansion of the requirements for high treatment accuracy and the expansion of the application, the asymmetric collimation system (or called the independent collimation system) has been developed, which still retains a pair of rectangular collimators. The collimator moves symmetrically, that is, it opens and closes symmetrically with respect to the center, while the other pair (usually the lower pair) of rectangular collimators opens or closes asymmetrically with respect to the center, and the rectangular collimator with asymmetric movement can Move each other across the center axis for a period of time on the opposite side.