Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 12 3 2025 07 01 557 563 EN Atefeh Tahmasebzadeh Research Committee, Department of Medical Physics, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Hosein Kaeidi Radiology Assistant, Department of Radiology, School of Medicine, Shahid Beheshti University of Medical Science, Tehran, Iran Maryam Kaeedi Neurology Assistant, Department of Neurology, School of Medicine, Tehran University of Medical Science, Tehran, Iran Reza Paydar Radiation Biology Research Center, Iran University of Medical Sciences, Tehran, Iran 2023 08 13 2023 12 04 Introduction: The use of CT scan in diagnosis is increasing significantly. The purpose of This study is evaluating the normal brain and chest Computed Tomography (CT) scans at six medical imaging departments in Tehran and evaluate the radiation dose and estimate the cancer risk associated with these normal CT scans. Materials and methods:  The data of 1080 patients between 20 to 50 years old referred to the six medical imaging centers in Tehran hospitals (1st January to 30th March) were collected. Patients were categorized into six groups according to their ages. In this study, a radiologist helped us in interpreting the CT scan images. The DRL was assessed and the BEIR VII model was used to estimate the radiation cancer. Results: Among the 1080 patients, 642 (59%) were males and the average age of the patients was 45.05 ± 22.60 years. Brain CT scans in 65% cases and chest CT scan in 52% were reported normal. The third quartile of CTDIvol, DLP, and ED values in the brain and chest scans were calculated and introduced as local DRL values. These values were determined as 22.13, 428.58, and 0.65 for CTDIvol, DLP, and ED values in the brain scan, and 5, 187.35, and 3.71 in the chest scan. The highest risk of cancer incidence in the brain scan was related to leukemia with a value of 0.73 per 100000 exposures, followed by thyroid with a value of 0.62 in women aged 20-25 years. And in the chest scan, the highest risk of cancer incidence was related to breast cancer with a value of 22.4 per 100000 followed by lung cancer with a value of 19.02 in the same age group. Conclusion: As the age decreases, the risk of cancer increases, therefore, by optimizing the radiation dose and avoiding CT scans without indications, the risk of cancer can be significantly reduced.  https://fbt.tums.ac.ir/index.php/fbt/article/view/794 https://fbt.tums.ac.ir/index.php/fbt/article/download/794/403