125I radioactive particles, also known as particle knife, is a new tumor treatment method that complements the defects of surgery and external radiotherapy in the international medical community. Its main feature is to implant 125I radioactive particles under the surveillance of B-ultrasound and CT for long-lasting radiation treatment of tumor, which has the advantages of small trauma, accurate target, low-dose continuous gamma radiation irradiation, no pollution, etc. The local tumor control rate can reach over 90%. 125I particle is an extremely advanced miniature sealed radioactive source. It is composed of a silver rod, adsorbed with the isotope 125I and titanium alloy shell, with a total length of 4.5 mm, cylindrical shape and diameter of 0.8 mm. 125I particles release X-rays with energy of 27.4-31.4 KEV and γ-rays with 35.5 KEV, with a half-life of 60.1 days and a full-life of 400 days. The radioactive source 125I particles are permanently implanted into the tumor lesion and around the lymphatic system through surgery or percutaneous puncture to cause cell degeneration and necrosis, thus achieving the purpose of tumor treatment. Inter-tissue brachytherapy with 125I particles is the clinical application of atomic physics in medicine, which is one of the high-tech treatments in modern medicine. After the mid-1980s, 125I intra-tissue radiotherapy for cancer treatment has been widely used in Europe, the United States, Australia and other countries. Take prostate cancer as an example, the experience of 125I inter-tissue brachytherapy for prostate cancer at Senttle Prostate Cancer Treatment Center in the United States for more than 10 years shows that the cure rate reaches 96.5% and does not affect the physiological function of patients. After years of clinical application results in Europe and America, it was found that all solid tumors except leukemia can be treated with 125I particles. It has obvious efficacy on prostate cancer, head and neck cancer, lung cancer, liver cancer, pancreatic cancer and soft tissue malignant tumors, and has greatly improved the quality of life for patients after treatment. Nowadays, 125I endoradiotherapy has been used as the preferred modality for cancer treatment in many foreign cancer fields.