Contact beam limiter

Electron beam limiters are divided into contact beam limiters and non-contact beam limiters. So what is contact beam limiters? Next, let’s take a look

1. The shape of the shape contact beam limiter is conical or barrel. It can be fixed or adjustable.

2. Material The electron beam limiter material is made of low atomic number material, and the selection of material directly affects the quality of the electron beam used for treatment. In order to reduce the share of bremsstrahlung generated by the electron beam in the beam limiter, materials with lower atomic number should be used. However, the use of materials with lower atomic number will generate significantly more low-energy electrons into the electron beam, so it is necessary to choose the best atomic number.

3. The use of the beam limiter wall has the function of scattering electrons, which can improve the evenness. During use, the bottom of the beam limiter should be directly contacted with the patient’s skin, otherwise the evenness will change significantly with the distance from the end face of the beam limiter. Although the risk of the patient being squeezed has been taken into account in the design, most of them are equipped with compressible buffer springs, so it is still necessary to be very careful when using the motor-driven lifting treatment bed.

In addition, the electron energy scattered by the inner wall of the beam limiter is lower than that emitted directly from the radiation source, which will increase the surface dose, and the maximum absorbed dose point will move towards the surface, reducing the steepness of the dose drop at the end of the range. The average energy of the electrons scattered into the electron beam by the wall of the electron beam limiter is about 40% lower than that of the incident electron beam. Therefore, shallow “hot spots” will be formed at the edge of the field. In order to reduce this effect, high-density materials are generally used at the edge of the electron beam limiting cylinder, such as 1mm tungsten metal as a bushing. The above is the contact beam limiter. If you need it, please consult. Tel:+8617616362242                                                                                                      

Author:X Ray Collimator