I. Basic Concept and Scope of Particle Implantation Therapy 1. Concept: Particle implantation is one of the contents of brachytherapy, and its basic practice is to put the closed radioactive source with certain specifications and activity into the human body tissues through minimally invasive way to irradiate the tumor tissues with high dose, so as to achieve the purpose of treating the tumor. 2. Characteristics of particle morphology: radioactive particle implantation can only be a broadly defined means of targeted therapy, which strictly speaking belongs to radiation therapy. Commonly used radionuclides such as 125I, 106pd, etc. have long half-life, respectively 60 days and 17 days. However, the energy of r-rays produced is very low, with a range of 17mm within the tissue, which can produce a high radiation dose locally.125I, 106pd are sealed by high-density needle alloy tubes to form 4.8mm×0.8mm seeds, which are implanted into tumors with the help of surgery, ultrasound, and CT guidance to irradiate tumors at a close distance and for a long period of time. Second, particle implantation method: applying ultrasound guidance, CT, MRI positioning technology, the accuracy of the implantation position is fully guaranteed, the dose distribution in the treatment target area is more ideal, and it is better than the conventional treatment while improving the therapeutic effect, with fewer side effects and higher quality of life. Significantly reduced treatment complications. Particle implantation is divided into temporary implantation and permanent implantation. Temporary implantation is characterized by high activity of radioactive source, mostly high dose irradiation, and most of them need to be removed by surgery again. For permanent implantation, the activity of radioactive source is small, and the particles stay in the tumor body for a long time. Specific implantation methods: 1, template implantation; 2, ultrasound or CT-guided implantation; 3, intraoperative direct implantation; 4, three-dimensional stereotactic implantation; 5, direct implantation with the help of various scopes. Biological advantages of radioactive particle implantation therapy: 1. Tumor tissue is composed of parenchymal cells (tumor cells) and mesenchymal cells (blood vessels and connective tissue). The sensitivity of tumor tissues to radiation follows the B-T law, i.e. the sensitivity of human tissues to radiation is directly proportional to the reproduction ability and inversely proportional to the degree of differentiation. The stronger the reproductive ability, the more sensitive the tissue is to radiation, and the lower the degree of differentiation, the more sensitive the tissue is to radiation, and vice versa. The radiosensitivity of tumor tissues is regulated by oncogenes and oncogenes, and the difference between tumor tissues and normal tissues is manifested in value-added ability, differentiation ability, regeneration ability and microvascularity of tissues. 3.Tumor cells have uncontrolled unlimited proliferation ability, but due to space limitation and insufficient vascular supply, which causes part of tumor tissues to stop proliferating and stay away from the vascular cell layer, becoming the layer of anoxic cells and necrotic layer, and necrosis occurs in tumors with a radius of more than 200um. The existence of oxygen-depleted cells is an important factor affecting radiosensitivity. 4.The radioactive damage of cells is divided into lethal damage, sub-lethal damage, and potential lethal damage. Advantages of radioactive particle implantation: 1. There is a three-dimensional treatment plan design, which can accurately complete the three-dimensional morphology reconstruction of the tumor and the surrounding tissue relationship, and accurately design the position and quantity level of implanted particles to be applied into the path. It meets the requirements of specific and individualized optimal design of target area dose. 2.It clearly improves the acceptable dose to the tumor target area, achieves high dose target area fitness, and reduces the complication of radiation damage. 3.Improved radiosensitivity, low-dose continuous irradiation, uninterrupted irradiation of tumors with different division cycles, and high radiobiological effect. 4.It can effectively protect the surrounding normal tissues. The radiation distance of radioactive particles in the tissue is short, only 1.7 cm, and the dose distribution outside the target area can be well controlled by adjusting the spacing and activity of the particle source. 5, radioactive particles for titanium alloy encapsulated micro-particles, and the human body has better tissue compatibility, and will not produce radiation leakage and pollution of the treatment path. 6.Simple operation, small trauma, low cost of equipment and treatment. 7, protection and safety, short half-life, low-energy, low-activity closed radioactive sources are always placed in special containers, the surgical process will not be irradiated by particles. 8.Radiation complications are much lower than external radiation therapy. Solve the external radiation sub-irradiation, short-term insufficient, due to breathing up and down to move the thoracic cavity malignant tumors, receiving radiation dose is not uniform and due to the external radiation radiation source intensity, resulting in complications such as obvious shortcomings. V. Scope of treatment: Radioactive particles were firstly approved by FDA for the treatment of prostate cancer, and now it is also applied to lung cancer, liver cancer, glioma, nasopharyngeal carcinoma, oral cancer, rectal cancer and so on. Especially for lung cancer, liver cancer and local bone metastasis or other soft tissue metastasis, etc., it is relatively safe and mature, with good curative effect.