Broadly speaking, radiation therapy includes both radiation therapy for tumors in the Department of Radiation Therapy and internal isotope therapy in the Department of Nuclear Medicine (e.g., iodine 131 for thyroid cancer and hyperthyroidism, and Phosphorus 32 for cancerous pleural fluid, etc.). Radiation therapy in a narrow sense generally refers only to the former, i.e., what is commonly known as radiation therapy for tumors. Radiation therapy has two types of irradiation: one is long-distance radiotherapy (external irradiation), which is to keep a certain distance between the radiation source and the patient's body for irradiation, and the rays penetrate from the patient's body surface to a certain depth in the body to achieve the purpose of treating tumors, which is the most widely used and the most important; the other is close radiotherapy (internal irradiation), which is to place the radiation source in a sealed place within the tumor or on the surface of the tumor, such as into the natural cavity of the human body or within the tissue, and the other is to place the radiation source in a sealed place within the tumor. The other one is brachytherapy (internal irradiation), in which the radioactive source is sealed and placed inside the tumor or on the surface of the tumor, such as into the natural cavity of the human body or inside the tissues (such as the tongue, nose, pharynx, esophagus, trachea, and uterus) for irradiation, i.e., using the intracavity, inter-tissue insertion, and modeling of the way of dressing for the treatment. In recent years, with the continuous improvement of medical equipments in hospitals, brachytherapy has been popularized.
There are three basic differences between in vivo and ex vivo radiation therapy: ① compared with in vitro irradiation, in vivo irradiation, the intensity of the radiation source is smaller, from a few milli-curies to about 100 milli-curies, and the therapeutic distance is shorter; ② ex vivo irradiation, most of the energy of the radiation is shielded by collimator, beam limiter, etc., and only a small portion of the energy reaches the tissues; in vivo irradiation is the opposite, and most of the energy is absorbed by the tissues; ③ ex vivo irradiation, the radiation must pass through the skin and normal tissue to reach the tumor, the tumor dose is limited by the skin and normal tissue tolerance, in order to get a high and uniform tumor dose, the need to choose different energy rays and the use of multi-field irradiation technology, etc.; and in vivo irradiation, the radiation up to the tumor tissue, the deeper part of the normal tissue by the irradiation amount is very small.
According to statistics, about 70% of cancer patients need to be treated with radiation therapy in the process of cancer treatment, and about 40% of pain can be cured by radiotherapy. The role and status of radiation therapy in tumor treatment is becoming more and more prominent. Radiation therapy has become one of the main means of treatment of malignant tumors.