الفهرس 
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Abstract
Introduction:It is important to study the characteristics of diagnostic X – ray machines and the factors that affecting the beam quality and the dose delivered to patients such as reproducibility of tube voltage, dose output, exposure time, accuracy of KVp, exposure time (msec), mAs linearity, and half value layer to reduce the dose delivered to patients. The examinations of these factors are studied using noninvasive KV meter. When taking radiographs, the association of the tube current, exposure time, kilo-voltage and filtration of the x-ray beam are factors affecting the photons number and the spectrum of energy. The main goal of a radiology quality control program is to reduce the exposure dose for patient, increasing the efficiency and the long-life of machines, and improve quality of image. The determination of effective energy is important to characterize of the radiation qualities in X – ray systems used to calibrate of instruments. The effective energy of diagnostic x-rays is important for quality assurance and quality control purposes. All X – ray machines do not always produce the same quality of x-rays for a given voltage. This may be due to incorrect calibration, age of machines, wave form and other causes. Diagnostic x–ray beam quality is usually expressed by means of the KVp and the filtration or, the half–value layer (HVL) in millimeters of aluminum. The effective energy is used for expressing an X-ray quality by one numerical value. When beam quality is expressed by using HVL and the effective energy, it is necessary to describe the tube potential, and the homogeneity coefficient. It is not an easy comparison to express the quality of the diagnostic X-rays, and to calculate physical characteristics of the X-rays by using the effective energy.Half value layer (HVL) is the most frequently used quantitative factor for describing both the penetrating ability of specific radiations and the penetration through specific objects. Another parameter used to describe the penetrating ability of a beam is the homogeneity coefficient. When a polychromatic beam passes through an absorber, photons with low energy are attenuated more rapidly than photons with high energy, the quality of the beam change with increasing amounts of an absorber. The added filtration reduces the intensity of the x–ray beam, increases the HVL, decreases patient exposure, and improves image quality for a given radiation dose. A practical way of expressing the penetrating ability of x–ray beams from x–ray tube is by using the concept of HVL, which must be measured under narrow–beam geometry conditions. The determination of effective energy is important to characterize of the radiation qualities in X–ray systems used to calibrate of instruments. Materials: Three conventional X – ray machines in radiology department at UROLOGY and NEPHROLOGY center in Mansoura were under investigation. Aluminum sheets X2 Ray safe sensor and SpekCalc program. Results:The quality control tests for x – ray machines were good for all machines and were within the tolerance limit. The values of x–rays examinations are measured and compared with the international tolerance limit. The measurements were done through quality control tests as acceptance procedures. There was a difference between the results of HVL, HC and effective energy determined from measurements of Toshiba x-ray machine for the range of x-ray energy peaks from 40 to 100 KVp and the HVL, HC and effective energy estimations of SpekCalc program. Ensure the reduction of the dose and keep the patient from exposure to doses of excessive radiation and maintain the quality of the image and not to repeat the process once again and maintain the age of machines and quality and therefore must spread quality control program in all hospitals in Egypt to ensure the quality of the x-ray machines. SpekCalc program showed a slight difference with the measured HVLs and effective energies from direct measurement from Toshiba X-ray machine. The SpekCalc program is user-friendly in predicting HVLs, and effective energies used for characterizing the X-ray beam quality, and this program provides predictions compared with experimental values of the X-ray machines.