en Radiation Biology Radiation Biology تحقيق بديع Original Research <p align="center"><strong>  ABSTRACT </strong></p><p> <strong> Background: </strong>While the benefits of Computed Tomography (CT) are well known in accurate diagnosis, those benefits are not risk free. CT is a device with higher patient dose in comparison with other conventional radiological procedures. Is the reduction of exposures by requiring optimization of CT procedures [a principle concern in radiological protection]? In this study, the radiation dose of conventional and spiral CT were investigated and compared with European Commission Reference Dose Levels (EC RDLs). </p><p> <strong> Materials and Methods: </strong>The dosimetric quantities proposed in the European Guidelines (EG) for CT are Weighted Computed Tomography Dose Index (CTDI_W) for a single slice for axial scanning or per rotation for helical scanning and Dose-Length Product (DLP) for a complete examination. The patient-related data were collected for brain, neck, chest, abdomen and pelvis examination s in each scanner. For each type of examination, 10 typical patients were randomly included. CTDI with an active length of 10cm was measured in two CT scanners by using UNFORS (Mult-O-Meter 601) in head and body phantom (PMMA) with 16 cm and 32 cm in diameter respectively. Mean values of CTDI_W , DLP and Effective Dose(ED) were estimated for those examinations . </p><p> <strong> Results: </strong>CTDI_W had a range of 15.8-24.7 mGy for brain, 16.1-30.6mGy for neck, 6.8-9.2 mGy for chest, 6.8-9.8 mGy for abdomen and pelvis. DLP had a range of 246.4-397.7 mGy.cm for brain, 104.6-262.2 mGy.cm for neck, 135-248.4 mGy.cm for chest, 187-298.9 mGy.cm for abdomen and 197.2-319.4 mGy.cm for pelvis. The mean values of effective dose were 0.74 mSv for brain, 0.9 mSv for neck, 3.1 mSv for chest, 3.7 mSv for abdomen and 5 mSv for pelvis. </p><p> <strong> Conclusion: </strong>The obtained results in this study have shown that CTDI_W and DLP are lower than EC RDLs and other studies, in other words , the performance of all scanners has been satisfactory as far as CTDIw and DLP are concerned. The CTDI_W and DLP in the conventional CT are higher than the spiral CT values . With regard to ALARA principle, for the establishment of reference dose levels, the radiation dose with spiral CT scanners should be taken into account. </p> ,CTDIw,patient dose,CT, DLP,RDLs 183 189 http://ijrr.com/browse.php?a_code=A-10-1-175&slc_lang=en&sid=1 F. Bouzarjomehri Bouzarj_44@yahoo.com 79003194753284600482 79003194753284600482 Yes M. H. Zare 79003194753284600483 79003194753284600483 No D. Shahbazi 79003194753284600484 79003194753284600484 No