Inter-tissue brachytherapy with radioactive particles (commonly known as “particle knife”) is a very important tool and a newest method to treat tumors. The radioactive 125 iodine, which has the effect of killing tumor cells, is placed in a metal titanium shell, sealed and made into a short rod of less than half a centimeter in length, like a 0.7mm pencil lead used by elementary school students, and called “particle”. The size of the tumor shown on the patient’s CT and MR films is then input into a three-dimensional stereotactic planning system, which reduces it to a three-dimensional image of the actual size of the tumor, and then precisely distributes the particles in certain locations at intervals of one centimeter long and one centimeter wide. According to this treatment plan, doctors use minimally invasive techniques such as lumpectomy, percutaneous puncture, etc. under the guidance of CT, B-ultrasonic, etc., and use a set of special instruments to place radioactive particles directly into the tumor or permanently bury the tumor bed, sub-tumor area and possible metastatic lymphatic pathways that cannot be cleanly cut during surgical operation. Radioactive particles. The γ-rays emitted by these particles inside the tumor can rapidly kill the tumor cells and cut off the pathway of tumor cells spreading, which is a kind of particle implantation technology that is exactly the same as the tumor form, thus achieving the same effect as scalpel resection, so it is also called “particle knife”.