One of the most widely used methods for the screening of cancer patients today is PET/CT. The most widely used radiopharmaceutical in PET/CT imaging is fluorine-18 deoxyglucose (18F-FDG). PET/CT imaging is performed 40-60 min after intravenous injection of F18-FDG to the patient. After the FDG injection, the patients transmit radiation to the environment. The emitted radiation dose rate varies according to the activity of the radioactive substance given to the patient. In this study, the dose rate of radiation emitted from FDG-injected patients was determined both by distance and by time. The results obtained are compared with similar studies. In terms of radiation safety, the required distance between the patient and the radiation worker is calculated. This calculated distance varies according to the time of injection, since fluorine-18 radioisotope has 110-min half-life.