Patient Dose Assessment And Optimization Of Pelvic Radiography With Digital X-Ray Systems

ABSTRACT

Low doses of ionizing radiation are delivered to the area of clinical interest in projection radiography. However, the application of digital radiography systems (DRS) is characterized by higher doses than film-screen radiography. Radiation exposure of the pelvis is of primary concern because of the radio sensitive reproductive organs in the pelvic region. For the radiation protection of patients, dose monitoring is essential in pelvic radiography and whenever possible, dose and image quality must be optimized to ensure safety of patients. The aim of this study was to assess the entrance surface dose (ESD) and effective dose (ED) to patients undergoing pelvic X-ray examinations with computed radiography (CR) systems, and develop dose and image quality optimization strategies with the aid of an anthropomorphic phantom. Hence, determine the optimum exposure factors for AP pelvic examinations. This was to serve as basis for dose and image quality optimization in pelvic radiography. Patient and phantom radiographic image quality was assessed in terms of signal-to-noise ratio (SNR). The dose and image quality was assessed for 102 patients. Twenty-four different exposures with varying tube potential (kVp), tube current (mAs) and focus-to-detector distance (FDD) were made for the optimization studies. Results of patients‟ dose estimation showed that the 3rd quartile ESD of 2.56 0.60 mGy for pelvis AP radiography was lower than DRLs by at least 24% with ED of 0.27 0.07 mSv. The mean SNR of patients‟ radiographs was 8.5 2.2 which is 70% higher than the recommendation by the Rose model. After the phantom optimization process, the optimum exposure factors were 70 kVp, 12.5 mAs and 100 cm FDD giving ESD and SNR of 1.09 mGy and 16.23 respectively. It was found that the dose could be reduced further by using lower kVp settings than what is currently xvi being used without degradation in image quality of the radiographs. The dose at the optimum exposure factors was reduced by 29.2% with 65 kVp, 12.5 mAs and 105 cm FDD. Thus the SNR of the image reduced by 19.6% to a SNR of 13.0404, which is still of optimum diagnostic quality.