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Background: Designing and shielding of an appropriate radiography room has been one of the major concerns of radiation scientists since the first decade after the invention of X-rays. Recently, report No.147 of National Council on Radiation Protection and Measurements (NCRP) has been published. In this study the researchers have investigated the effect of new report recommendation on primary and secondary barriers thicknesses in comparison to NCRP 49, and 116 recommendations. Materials and Methods: To calculate the walls thickness of a conventional radiography room, the workload of a radiography room of a university hospital was determined by recording the number of exposures, mAs and kVp for each patient during six months. Three types of calculations were done: (1) Using NCRP 49 formulations and dose limits (2) Using the NCRP 49 formulations and NCRP116 dose limits and (3) Using the NCRP 147 recommendations. Results: The estimated workload was 172 mA min wk-1 for the studied radiography room which was slightly lower than the workload recommended by NCRP147. The results showed that using the NCRP49 formulation and NCRP116 dose limits, the barriers thickness increases substantially. Moreover, the dose limits were lower in NCRP 147, using the third method. The primary barrier thickness is decreased considerably in comparison to two other methods. For the secondary barrier the results of the two methods (1) and (3) did not differ and remained the same. Conclusion: Application of NCRP 49 and NCRP116 dose limits for radiography room shielding (second method) overestimated the primary and secondary barriers thickness, significantly. But, applying NCRP 147, not only the new dose limits were considered, but also the cost of primary barrier construction was reduced. Iran. J. Radiat. Res., 2009 6 (4): 183-188

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Background: X-ray computed tomography (CT) examinations deliver a significant amount of radiation doses to patients comparing to conventional radiography examinations. The objective of the current study was to analyze and investigate the average patient received dose from axial and spiral CT exams in a medical imaging center. Material and Methods: In this study, the patient imaging technique, weight and height were recorded. The patients’ doses provided by CT unit in terms of CTDIw were also recorded. Then, other dosimetric quantities including dose-length product (DLP) and effective dose were calculated for each patient using the recorded data. The average values were obtained for all the studied dosimetric quantities. Also, their distribution in terms of examined regions and imaging mode ie, axial and spiral CT were analyzed by SPSS software. Results: For all patients, the mean effective dose of 4.4 mGy with the standard deviation of 9.2 was found. The CTDIw for axial group was two times higher than spiral ones. Conversely, the effective dose of axial group was less than spiral group. Additionally, the effective doses of 2.3 and 5.2 mSv were found for axial and spiral, receptively. For both quantities of CTDIw and effective dose, the observed difference between axial and spiral modes were significant (P<0.001). Conclusion: Our results showed that although the patient doses in the current study was comparable with the reported values by similar studies in other countries, it was higher than the reported values of a similar study in Iran. Exposure technique’s optimaization and further review in routine CT examinations were recommended. Iran. J. Radiat. Res., 2012 10(2): 89‐94