Abstract
Background: 18F-fluorodeoxyglucose (FDG) is a radiopharmaceutical (radioactive tracer), generally used in the medical indicator on positron emission tomography/computerized tomography (PET/CT). PET/CT is an essential device for patients' diagnosis and their responses to treatment; it uses radioactive tracers for diagnosis. PET/CT is used with a special detector and worked with a computer to evaluate the sick organ and the functions of the tissues. PET/CT scanning is a special type of nuclear medicine indicator, highly used in clinics. In this study, we aimed to measure the level of radiation and its effectiveness in mentioned organs in PET/ CT devices. In the basis of this study, we want to reveal the level of radiation in different age range of patient's absorbed organ 18F-FDG. Methods: The absorbed organ's radiation level and the affected organ's radiation level were calculated in accordance with Monte Carlo (MC) methods. Results: The results for the patient's target organs in the used phantoms showed variations in age stages when compared with those determined by the MC simulation. These variances result from the structural anatomical differences in the age studied and in significant changes in the relation to their activity rate. Conclusion: The medical radiation which is exposed from PET/CT studies should be important in all the patients groups, furthermore, is more considerable in pediatric and adolescence patients. The As Low As Reasonably Achievable principle must be implemented in either by reducing the radiation dose on PET/CT or by considering alternative diagnostic imaging unit or device should be used.

Key words: Positron emission tomography/computerized tomography (PET/CT), florodeoxyglucose (18F-FDG), radiation protection.