The so-called internal radiation refers to brachytherapy, which is the opposite of external radiation. Clinically, internal radiation mainly includes the following ways: First, surface irradiation, for example, clinically applied dressing treatment for skin cancer hemangioma is surface irradiation. The so-called intracavitary irradiation refers to putting the radiation source into the natural cavity of human body, such as uterine cavity, nasopharyngeal cavity and esophageal cavity, which is used to treat cervical cancer, nasopharyngeal cancer and esophageal cancer, etc. Third, inter-tissue irradiation, inter-tissue irradiation is the insertion of the irradiation source into the tumor tissue according to certain rules, such as local insertion radiotherapy for breast cancer and tongue cancer, and also the placement of the irradiation source in the unresected tumor during surgery, and giving radiotherapy after surgery is also internal radiation.