Introduction: Nowadays, the absorbed dose of patients is on the rise due to the widespread use of computed tomography (CT) during the diagnosis process. Patients' doses for similar procedures are very different due to diversity in scanners and protocols. Hence, the purpose of this study was to determine the diagnostic reference levels for routine CT scan procedures in Kohgiluyeh and Boyer-Ahmad province, Iran. Material and Methods: In this study, four common brain, sinus, chest and abdominopelvic procedures (overall ۲۰۰ scans) in spiral mode were selected in five CT centers of Kohgiluyeh and Boyer-Ahmad province, Iran. Next, the doses were measured in head and body phantom, based on scan parameters of ten patients in each procedure at each centers (۲۰۰scans). Then, the third quartile of CTDIw was considered as the diagnostic reference dose. Finally, considering the pitch factor and the mean scan length in each protocol, the diagnostic reference level values based on the third quartile of the
dose length product (DLP) and volume CTDI (CTDIvol) were determined. Results: The dose reference level values according to CTDIw third quartile in the brain, sinus, chest and abdominopelvic procedures were ۳۹.۸۲, ۲۰.۸۸, ۱۴.۱۰ and ۱۷.۰۷ mGy, respectively. In terms of dose length product, the diagnostic reference level values in the above procedures were determined to be ۷۰۲.۷۵, ۲۴۳.۹۰, ۴۲۲.۰۲, ۸۶۵.۶۲ mGy.cm, respectively. Conclusion: The DRLs of the CTDIW, DLP and CTDIvol of brain and sinus scans calculated in this study, were comparable to other provinces, national DRL and eight other countries. However, the same quantities for the chest and abdominopelvic scans showed higher values compared to the mentioned studies, suggesting lowering mAs and increasing pitch number for patient’s dose optimization. In some centers to preserve image quality, it is necessary to optimize radiation conditions, especially for chest and abdominopelvic scans.