Radiotherapy, one of the three main methods of tumor treatment, is a technique that uses high-energy rays to kill cancer cells, either given from outside the patient’s body by an instrument or released by a radioactive substance placed in the body. The rays damage the DNA in the patient’s body that carries the cell’s genetic information, thus killing the cancer cells. More than 70% of cancer patients require radiation therapy as part of their treatment. Radiotherapy alone can cure a tumor, but radiotherapy can also be used in conjunction with surgery and chemotherapy as part of a comprehensive treatment to improve the cure rate of cancer. This shows the importance of radiotherapy in the treatment of tumor patients. Radiotherapy has been used as a means of treating tumors for more than 100 years. The most commonly used medical linear gas pedal was introduced into the clinic in the late 1840s. With the development of imaging technology, radiotherapy technology has been developed rapidly in recent times. Since the 1970s, radiotherapy has gradually entered the era of three-dimensional, intensity-modulated, image-guided precision radiotherapy. This has enabled radiation therapy to continuously improve the therapeutic effect while reducing normal tissue damage. The efficacy of radiotherapy alone is determined by several factors. The radiosensitivity of cells is an important factor. Cells from different types of tumors have different radiosensitivity. Highly sensitive tumor cells do not require very high doses to be killed, such as lymphoma and seminoma. Whereas, insensitive tumor cells require very high doses to be controlled, e.g., kidney cancer cells, melanoma, etc. In addition, the size of the tumor is also very important. Tumors with small volume can be treated well with radiotherapy. Tumors with large volume are very difficult to control. Therefore, some tumors can be cured with radiotherapy alone, while others need to be combined with surgery, chemotherapy and other integrated means to achieve a radical cure. Radiation therapy is a complex discipline integrated by several disciplines. The entire treatment requires a complete working team. This team includes: radiation oncologists (physicians), radiation physicists, radiation technologists and nurses. The radiation oncologist is a specially trained clinician who can develop the most appropriate radiation treatment plan based on the clinical characteristics of the tumor and the individual patient, using the appropriate radiation and radiation therapy techniques to precisely identify the area to be treated. Radiation physicists are involved in the design and quality assurance of radiation treatment plans, as well as maintaining the normal operation of radiation therapy equipment, and they are the workers behind the scenes. The radiation technologist is responsible for the operation of the radiation therapy equipment and the specific implementation of the radiation therapy plan designed by the physician and the physicist. Radiotherapy nurses, on the other hand, help patients understand radiotherapy and give care during treatment. It is clear that radiotherapy is different from other clinical disciplines. Each patient’s radiation therapy plan, the equipment used for radiation therapy, the length of treatment, and the side effects during treatment will vary from person to person. In modern precision radiotherapy, physicians use a variety of measures to ensure good reproducibility of each radiotherapy position. Marking the patient’s body with a marker is the most common method. Many people feel that this marker affects the aesthetics, but this marker is the therapeutic reference point for each patient during treatment, so it is important to keep the marker clearly visible during treatment, and if it is no longer clear, make sure to ask the doctor to retrace it! Due to the special nature of radiation therapy equipment, the treatment will be arranged in a closed environment without windows, and many patients will feel nervous when facing the huge machine. However, the radiation is actually invisible to the naked eye, and when receiving radiation therapy, the rays do not cause pain or discomfort, and the treatment time is only a few minutes. So try to relax and don’t be nervous. In addition, external radiation therapy does not cause radiation to the patient, so you do not have to worry about “irradiating” others during the whole treatment process. All in all, radiation therapy is an effective treatment for tumors with relatively limited side effects. With the rapid development of technology, the current equipment allows radiotherapists to increase the dose to the tumor and at the same time, control the chance and degree of side effects of radiotherapy. Patients do not need to be nervous during radiotherapy, but should relax and cooperate with doctors, technicians and nurses, and communicate any changes in their body during the treatment with doctors in time to complete the whole treatment successfully.