Recently, online articles about whether radiation from CT examinations can cause harm to the body and how likely it is to cause cancer have raised concerns. The articles mentioned that “the risk of radiation causing cancer is 1 in 4000”; “the small probability event of radiation-induced cancer is magnified due to the bias of perception, while the possibility of not causing cancer is downplayed”; ” The American College of Physicians stated in 2011 that the risk of cancer from radiation doses of less than 50 mSv (mSv, the equivalent dose unit for measuring radiation damage) per imaging examination, or multiple doses of 100 mSv in the short term, is undetectable because the dose is too low, or such risk does not exist at all”, etc. These statements make one wonder if radiation protection, which radiology has always emphasized, is not too strict and outdated. There is some scientific basis for the views in such articles. In 1990, the International Commission on Radiology recommended a dose limit of 1 mSv per year for any radiation caused by work and life, and an average of 20 mSv per year for 5 years for radiation workers, not exceeding 50 mSv in a single year. belongs to a relatively high dose of X-ray examinations (e.g., routine chest CT plain scan is about 4-8mSv). How does CT cause damage to people? CT examinations can be harmful, mainly because of the biological effects of relatively high doses of X-rays, which are high-energy particles that can damage the body’s cellular functions and metabolism when they penetrate the body. If the dose is not high, it will only produce short-term effects, and the body can repair itself, so the harm is relatively small. However, if the dose of X-rays is high, it will damage genes and produce various harmful biological effects, and as the radiation dose increases, the chance of biological effects will also increase. Biological effects include not only carcinogenic effects, but also effects in hematopoiesis, reproduction, genetics, growth and development, and hormone regulation. The occurrence and development of CT is a revolutionary progress in the medical field, and the rational application of CT examination can bring great convenience to the clinical diagnosis and treatment of diseases, such as the determination of acute cerebral hemorrhage, part of which CT has certain advantages. Used to detect early lung cancer, determine brain hemorrhage, vascular reconstruction, malignant tumor staging, etc. are very suitable, but what is said about using CT to diagnose gastric ulcer, pelvic CT to diagnose uterine fibroids, such belongs to simply unnecessary, because each disease has its most adapted examination method; ordinary pneumonia patients in a very short period of time repeated CT review, it is very easy to put the examinees in the danger of excessive radiation dose . Therefore, CT examinations should not be used and abused indiscriminately, in the case of the use or can be assured that, after all, one to two examinations will not cause serious harm So, when conducting CT examinations, we should strictly follow the three basic principles of the International Commission on Radiological Protection basic radiation protection. The first is the principle of justification, which must ensure that the application of ionizing radiation practice is less harmful to the population than the benefits; the second is the principle of optimization, which means that any exposure is kept at a reasonable minimum level to avoid unnecessary exposure; the third is the principle of limit, which ensures that the dose to the individual does not exceed the corresponding dose limit, so as to minimize the harm brought to the examinees by radioactive examination. If CT is used as a screening tool for tumor patients, it is undoubtedly a misuse of CT, but whether we need to do CT or not, if we use low radiation methods such as ultrasound, X-ray plain film, or non-radiation and non-invasive methods such as tumor gene mutation detection before doing CT, we can separate the healthy people from them. If we separate the healthy people from those who do not need CT, we can avoid the harm from CT.