Positron Emission Tomography (PET)/ Computed Tomography (CT) is a hybrid diagnostic technique which is used in medicine and biomedical research. One of the main advantages of this technique is the in vivo study of the metabolism of normal or pathological tissues. [1] PET/CT imaging is employed in nuclear medicine field and it utilizes short-lived radionuclides emitting positrons and provides molecular imaging of the organs. PET whole body imaging is a useful tool to identify early disease, distinguish benign from malignant lesions, inspect all organs for metastases, as well as determine an effective individual treatment. [1], [2] CT techniques provide attenuation correction of PET image data, anatomic information for diagnosis, staging and follow-up of the disease. For these purposes, CT imaging combined with PET has been proposed to optimize clinical images and contribute to more effective clinical processes. [3]

Diagnostic reference levels (DRLs) are a basic tool for the radiation protection of patients in ionizing radiation and they are not recommended doses. National DRLs are used in dose optimisation for every imaging technique using ionizing radiation. [4], [5], [6]The local medical laboratories are establishing DRLs on a regional level compared with the national DRLs, depending on the imaging modality available in every hospital.[7], [8] This process provides opportunity to avoid overexposure, as well as to ensure good practice in medical examinations according to ALARA (as low as reasonably achievable) principle. [9], [10], [11] The purposes of this study are to estimate the values of the radiation dose to patients and establish local Diagnostic Reference Levels (DRLs) of the combined PET/CT examinations in a large territory hospital in Greece (Evaggelismos General Hospital of Athens).