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Objective:To determine and optimize the radiation quality of the calibration system for mammography dosimeters in IAEA/WHO Secondary Standard Dosimetry Laboratory and to study the requirements for accuracy of thickness of the aluminum sheets used in the measurement, with a view to ensure the accuracy of the radiation quality.Methods:For the measurements of tube voltage and RQR-M radiation quality, a standard kV meter was used to determine the actual tube voltage value of the system under continuous exposure for 30 s by setting tube voltage of 25, 28, 30 and 35 kV, respectively, and aluminum sheet method was used to determine the first half value layer (HVL 1). The kV values were adjusted to make the reading of the standard kV meter as close as possible to its nominal value, so as to obtain the set kV value, actual tube voltage and HVL 1 per 1 kV within the nominal 25-35 kV range. For effects of different thickness of aluminum sheets on the result of HVL 1 measurement, a comparison was made between HVL 1 measured by aluminum sheet with thickness of 0.318 mm and 0.369 mm and HVL 1 measured under 18 different groups of aluminum sheet using a selected 30 kV tube voltage. Results:After the set kV values were adjusted, the actual tube voltage deviations from the nominal values under 25, 28, 30 and 35 kV were reduced from 0.55, 0.34, 0.33, 0.30 to 0.04, 0.02, -0.04, -0.01, and the HVL 1 deviations were reduced from 0.011, 0.007, 0.010, 0.012 to 0.000, 0.003, 0.003, 0.010, respectively. When the thickness differences between the two types of aluminum sheet and the reference HVL 1 were both within 0.1 mm, the deviations of the measured HVL 1 were all less than 0.01 mm Al, and the result was relatively accurate. However, when the differences exceeded that of 0.1 mm, most of the deviations of the measured HVL 1 were between 0.01 and 0.02 mm Al, and the measured result was not accurate. Conclusions:Although the RQR-M radiation quality of the calibration system was deviated, it is still within the range specified under the IEC 61267-2005. The radiation quality was closer to the standard values after fine-tuning the system tube voltage. In order to measure the HVL 1 more accurately, the thickness differences between the used aluminum sheet and nominal HVL 1 should not be greater than 0.1 mm Al.
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Abstract Objective: Derive filtered tungsten X-ray spectra used in digital mammography systems by means of Monte Carlo simulations. Materials and Methods: Filtered spectra for rhodium filter were obtained for tube potentials between 26 and 32 kV. The half-value layer (HVL) of simulated filtered spectra were compared with those obtained experimentally with a solid state detector Unfors model 8202031-H Xi R/F & MAM Detector Platinum and 8201023-C Xi Base unit Platinum Plus w mAs in a Hologic Selenia Dimensions system using a direct radiography mode. Results: Calculated HVL values showed good agreement as compared with those obtained experimentally. The greatest relative difference between the Monte Carlo calculated HVL values and experimental HVL values was 4%. Conclusion: The results show that the filtered tungsten anode X-ray spectra and the EGSnrc Monte Carlo code can be used for mean glandular dose determination in mammography.
Resumo Objetivo: Derivar espectros filtrados de raios X de tungstênio utilizados em sistemas de mamografia digital por meio de simulações Monte Carlo. Materiais e Métodos: Espectros filtrados por filtro de ródio foram obtidos para potenciais do tubo entre 26 e 32 kV. Os valores de camada semirredutora (CSR) dos espectros filtrados simulados foram comparados aos valores obtidos experimentalmente com um detector de estado sólido Unfors modelo 8202031-H Xi R/F & MAM Detector Platinum e unidade base 8201023-C Xi Platinum Plus w mAs em um sistema Hologic Selenia Dimensions utilizado no modo radiografia direta. Resultados: Os valores de CSR calculados mostraram boa concordância quando comparados com os valores obtidos experimentalmente. A maior diferença relativa entre os valores de CSR calculados com Monte Carlo e os valores de CSR experimentais foi 4%. Conclusão: Os resultados demonstram que os espectros filtrados de raios X de ânodo de tungstênio e o código de Monte Carlo EGSnrc podem ser utilizados para determinar a dose glandular média em mamografia.
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Background: Different computational methods have been used for the prediction of X-ray spectra and beam quality in diagnostic radiology. The purpose of this study was to compare X-ray beam qualities based on half-value layers (HVLs) determined through measurements and computational model estimations. Methods: The HVL estimations calculated by IPEM78 (Spectrum Processor of the Institute of Physics and Engineering in Medicine’s Report 78) and SpekCalc software were compared with those determined through measurements. In this study, the HVLs of both Philips (Phil) (Philips Healthcare, Best, NL) and General Electric Company (GE) (GE Global Research, Niskayuna, US) diagnostic range X-ray machines (50 kVp to 125 kVp) were evaluated. Results: In the HVL estimations, SpekCalc and IPEM78 showed maximum differences of 10% and 9%, respectively, compared with direct measurements. Both models provided means and SDs of HVLs that were within 5% of the HVL measurements of GE and Phil machines. Conclusion: Both computational models provide an alternative method for estimating the HVL of diagnostic range X-ray. These models are user-friendly in predicting HVLs, which are used to characterise the quality of the X-ray beam, and these models provide predictions almost instantly compared with experimental measurements.