Radiation therapy has a basic principle: to maximize the dose of radiation to the lesion area to kill the tumor cells, while leaving the surrounding normal tissues and organs with less or no unnecessary irradiation. To achieve this, there are some necessary conditions: First, it is required to be able to precisely locate the position of the tumor in the body and its relationship with the surrounding organs, at which time ordinary X-ray film can no longer meet our requirements. Only a device like CT can provide us with such information, which is not only a flat image, but can be reconstructed by computer in three dimensions so that we can see the area to be treated from all angles. Secondly, since the human brain cannot perform complex three-dimensional spatial operations, the help of a computer is necessary to complete the design of the treatment plan at this point. Computers can not only calculate the irradiated area appropriate to the shape of the tumor, but also precisely calculate the dose of radiation received by the tumor tissue and the surrounding normal organs in order to assess whether the treatment is safe and effective. Precision radiotherapy is one such treatment, which has certain advantages over normal radiotherapy. It can protect normal organs to a certain extent by exposing them to less radiation, and it can improve the efficacy by giving a more uniform dose to the tumor area to be irradiated. Therefore, it is a widely used treatment modality nowadays. However, precise radiotherapy is not applicable to all radiotherapy treatments. In some cases, it can be applied but it is not very meaningful and increases the cost burden of patients. For example: superficial tumors of the skin, preventive irradiation of certain lymph node areas, radiotherapy of the whole brain, radiotherapy of bone metastases, etc. It is recommended that you consult your doctor more often to make the right choice.