The development of pet-ct technology has provided a lot of very meaningful information for the diagnosis and staging of tumors, and the population of pet-ct check-ups has been growing in recent years, accompanied by people’s concern about the radiation of pet-ct. With the promotion of large medical equipment Positron Emission Tomography /Computed Tomography (pet-ct), more and more people have started to contact and accept pet-ct testing and tumor screening, and even used for health check-ups. With the media’s publicity about nuclear accidents and nuclear military knowledge abroad, the public has received more knowledge about radiation safety, and some people have started to realize the radiation problem of PET/CT examinations like other radiological examinations, and have questions about the radiation safety of pet-CT examinations, “Is PET/CT examination safe in the end? How long is the interval between exams?” PET-CT has been used in China since 2002, and with the continuous upgrading of PET-CT equipment, the dose of nuclide used in PET is getting smaller and smaller, the scanning speed of CT is getting faster and faster, and the radiation dose control is getting better and better, there is a need to re-understand the amount of radiation and safety of PET-CT examinations. There is a need to re-conceptualize the issue of radiation dose and safety of pet-ct examinations. The source of radiation dose of pet-ct comes from radionuclide and X-CT, among which, most of the radioactive radiation used in PET comes from fluorine-18 (18F), 18F emits positron and produces high-energy γ-rays, which has certain radiation to human body, and the radiation dose is about 2.1×10-2mSv/MBq, generally 222-296 MBq is used in one examination, i.e. The radiation dose from the nuclide required for PET scan is about 4.6-6.2 mSv, but with the modernization of the equipment, the third generation of pet-ct products, the dose of radionuclide used can be reduced to about 185 MBq, and the radiation dose to the patient is reduced to about 3.8 mSv. The radioactive drug used is a physiological metabolite. The radionuclide used is an analogue of physiological metabolites, such as 18F-FDG, which is an analogue of glucose and is non-sensitizing and does not pose any harm to human body. The radionuclide used is an ultra-short half-life isotope that decays rapidly and disappears completely from the body within a few hours. By drinking more water and accelerating the excretion of the drug, the total dose of radiation received by the patient from the nuclide can also be reduced appropriately. The main source of radiation dose for pet-CT examinations is the CT scan, but the CT used for PET/CT has a lower dose than conventional CT. In the past, the radiation dose from older generation CT examinations was much higher, generally above 18 mSv, while the CT scans in pet-CT generally used lower electric flow acquisition, and the radiation dose was less than 1/2 of the radiation dose from conventional CT scans, according to a study by the University of Hong Kong. However, with the modernization of PET/CT, pet-ct is also equipped with more advanced CT, which shortens the scanning time and significantly reduces the radiation dose. The radiation dose for a single whole-body examination with PET-CT is reduced from about 15 mSv to about 7.5 mSv (7.0 to 10.2). However, if high mA scan mode or enhanced scan mode is used, the CT dose can be as high as 14.1 to 18.6 mSv, so the increased dose in the pet-ct scan mainly depends on the CT scan mode, and low dose (low mA) scan mode is generally recommended for CT scans in routine pet-ct imaging, and a diagnostic dose scan is used locally for suspicious organs to minimize the radiation dose to the recipient. The dose of radiation to the recipient is minimized. After all, pet-ct examination has a certain radiation dose, as with other medical examinations and treatments, such as taking medicine, although it can treat diseases, but there will be certain side effects, when using to weigh the pros and cons; also such as surgery can effectively treat diseases, but may also bring a certain amount of tissue and organ structure or function of damage. Therefore, any medical treatment should be based on patient benefit, i.e., find the best node in the cost-benefit, strictly grasp the indications for pet-ct examination, and adopt the principle of justification and optimization in using pet-ct examination, so that the benefit received by the examinees is obviously greater than the risk. For active prevention of tumors, early detection and early treatment, 70% of malignant tumors can be avoided and 90% can be cured. A survey in the United States showed that 87% of respondents approved of routine cancer screening, and 68% of women believed that screening could prevent or reduce the risk of breast cancer. The National Cancer Society estimates that 30 to 35 percent of premature deaths from cancer can be prevented with proper screening. Screening data for lung malignancies show that 80% of positive pet-CT lung findings are for stage I lung cancer. Because PET/CT has improved the accuracy of early diagnosis, staging, and differentiation of benign and malignant nodules in lung cancer, pet-ct examination is perhaps the best early diagnosis method for lung cancer, and even systemic solid tumors. Some scholars have also shown that the median survival of patients with non-small cell lung cancer who received radical radiotherapy or chemotherapy with or without 18F-deoxyglucose (FDG) PET to determine tumor stage before treatment was nearly double. pet-ct examination is used in the diagnosis and differential diagnosis of tumor; staging and re-staging of tumor, degree of differentiation; identification of tumor recurrence; guidance of tumor treatment plan; evaluation of tumor treatment efficacy; assessment of tumor prognosis; search for primary and metastatic foci of tumor in tumor high-risk patients such as blood tumor markers are continuously increased and tumor families, as well as in the diagnosis and treatment assessment of neuropsychiatric diseases and cardiovascular diseases. The examinees can get greater benefits. Although pet-CT is associated with a certain amount of radiation, the benefits of PET/CT for patients with indications clearly outweigh the risks of radiation exposure and may even result in life-saving opportunities. The decision to repeat PET/CT for patients with suspicious lesions or changing conditions can be based on the condition and the need for treatment decisions, and should not be abused indefinitely.