When it comes to radiation therapy, there are generally two extreme views. On the one hand, many people will talk about radiation therapy, thinking that radiation therapy will definitely be accompanied by pain, and even associate it with death, thinking that radiation therapy is harmful and not beneficial. On the other hand, some people imagine radiation therapy to be very simple, thinking that it is just to irradiate the patient lying on the machine, and some tumor patients, once admitted to the hospital, immediately say to the doctor, “Let’s start radiation therapy right away”. Radiation therapy for tumors is a local treatment method using radiation to treat tumors. Radiation includes α, β, γ rays produced by radioisotopes and x-rays, electron beams, proton beams and other particle beams produced by various types of x-ray therapy machines or gas pedals. About 70% of cancer patients need to be treated with radiation therapy in the course of treatment, and about 40% of cancers can be cured radically with radiation therapy. CT localization before radiotherapy Patients need to do a CT localization before formal radiotherapy, and need to collect CT images to find the location of the tumor.CT can be based on the different tissues of the human body to the different absorption and transmission rate of X-rays, the application of highly sensitive instruments to the human body to carry out measurements, and then the measurement of the data obtained by the input of electronic computers, electronic computers to process the data, can be photographed the human body is the cross-section or three-dimensional part of the examination. After processing the data, the computer can take a cross-section or three-dimensional image of the part of the body being examined, and discover small lesions in any part of the body. After the CT, the doctor marks the location of the tumor on the patient’s body so that the rest of the treatment process can proceed smoothly. Importance of Physicists Before the patient undergoes radiation therapy, the physicists also customize a treatment plan for him. Physicists are very, very important members of oncology radiation therapy, and it is not an exaggeration to say that without them, radiation therapy cannot be carried out. Especially with the rapid development of tumor radiation therapy equipment and technology in recent years, the role of physicists in ensuring radiation safety, improving the level of therapeutic technology, and providing patients with high-quality services is becoming more and more important. Physicists have a long history as a profession in oncology radiotherapy departments in European and American hospitals, and the number of physicists engaged in the profession is also increasing due to the development of equipment and precise radiotherapy techniques, while the responsibility they bear is also getting heavier and heavier. Image Guided Radiation Therapy (IGRT) is a four-dimensional radiation therapy technique, which adds the concept of time factor on the basis of three-dimensional radiation therapy technique, takes into full consideration the movement of anatomical tissues in the treatment process and the displacement error between treatments, and utilizes a variety of advanced imaging equipments for real-time monitoring of tumors and normal organs before and during the treatment of the patients. Before and during the treatment, various advanced imaging equipments are used to monitor the tumor and normal organs in real time, and adjust the treatment conditions according to the changes in the position of the organs, so that the irradiation field closely “follows” the target area, which makes it possible to achieve accurate treatment in the true sense.