What is Stereotactic Radiation Therapy? The concept of Stereotactic Radiosurgery (SRS) became a new discipline with the invention of the Gamma Knife and the good treatment results. Around the concept of stereotactic radiosurgery, different medical devices were invented and new technologies emerged. In the 1980s, Colombo and Betti and other scholars improved the medical linear gas pedal by adding a stereotactic system and collimator, using a non-coplanar multi-arc small-field three-dimensional beam to irradiate the lesion, achieving similar treatment results as the Gamma Knife. This modified linear gas pedal is called the X-knife (X-knife). It is generally used for fractionated treatment and is known as stereotactic radiotherapy (SRT) in academic circles. In the 1990s, linear gas pedal three-dimensional conformal radiation therapy (3 dimensional conformal radiation therapy, 3DCRT) and intensity modulated radiation therapy (IMRT) technology, whole-body gamma knife and body gamma knife have gradually matured. and body gamma knife and other devices belong to the category of stereotactic radiation therapy. It is characterized by three-dimensional, small-field, focused, fractionated, high-dose irradiation. SRT is currently divided into two categories according to the size of the single dose and the degree of field clustering. The first category of SRT is characterized by the use of three-dimensional, small-field, cluster, fractionated, high-dose (much larger than conventional fractionated doses) irradiation. These all use multi-arc non-coplanar rotational focusing techniques, and the additional tri-polar collimators are generally circular. The second type of SRT is conventional fractionated radiation therapy using stereotactic techniques. 3DCRT, especially IMRT, falls into this category. Stereotactic radiotherapy and stereotactic radiosurgery are two concepts that can be easily confused, and they have both similarities and distinct differences. The similarity is that under stereotactic orientation, different techniques are used to maximize the irradiation dose to the target area and reduce the amount of tissue exposed outside the target area. The difference lies mainly in the accuracy of positioning and the degree of dose attenuation outside the target area. SRT has a larger error than SRS, and the attenuation of radiation dose outside the target area is not as steep as that of SRS. For this reason, SRT has not yet reached the level of “surgery”, which determines that SRT is a multiple high-dose treatment (larger than conventional radiotherapy fractional dose, smaller than SRS), while SRS is a one-time high-dose treatment. In any case, SRT has developed the site of stereotactic radiotherapy to the whole body, which basically represents the current development direction of tumor radiotherapy in the world, and is suitable for treating malignant tumors in the body and high-grade brain malignant tumors.