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Measurement of radiation doses to patients undergoing routine X-ray examinations in Windhoek, Namibia to develop diagnostic reference levels
Daniels, Edwin Ralph
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Background: The National Radiation Protection Authority (NRPA) of Namibia was tasked in 2005 by the IAEA under the project RAF9/033 to develop diagnostic reference levels for conventional radiographic examinations. To date, no study that examines the radiation dose in diagnostic radiology has been undertaken in Namibia and radiation protection of patients may not be optimised. Diagnostic reference levels acts as a quality assurance tool that identifies procedures or activities where patient doses are high. Objectives: The purpose of the study was to develop local Diagnostic Reference Levels (LDRL’s) for commonly performed conventional radiography projections in Windhoek, Namibia. The objectives of the study were to: • Measure KAP (Kerma Area Product) for postero-anterior (PA) and lateral (LAT) chest, antero-posterior (AP) and LAT lumbar spine, AP pelvis, and PA and LAT skull projections. • Calculate entrance skin and effective doses from the recorded KAP values. • To compare the KAP, entrance skin doses and effective doses with internationally established reference levels for the same procedure as well as similar studies in Africa. • Develop conversion coefficients from KAP values for estimation of effective and skin doses in clinical practice. Method: In this study, three (3) hospitals located in Windhoek, Khomas region were selected and KAP measurements were recorded on 218 patients with a mean weight of 70±5kg.The entrance skin, and effective doses were calculated through Monto Carlo simulations by entering the geometric data, exposure parameters and equipment specifications and KAP values into PCXMC 2.0 software (Finland). Diagnostic Reference levels (75th percentile), entrance skin doses (ESDs) and effective doses were calculated for anterior (PA) and lateral (LAT) chest, antero-posterior (AP) and LAT lumbar spine, AP pelvis, and PA and LAT skull projections. Results: The 75th percentiles of the entrance skin doses combined for PA and LAT chest, AP and LAT Lumbar spine, AP Pelvis and PA and LAT skull were, 0.0333 mSv, 0.0663 mSv, 0.1970 mSv, 0.2740 mSv, 0.2497 mSv, 0.0922 mSv, and 0.0584 mSv respectively. The effective doses for the same procedures were 0.0545 mSv, 0.0942, 0.3792, 0.2970 mSv, 0.3061 mSv, 0.0267 and 0.0283 respectively. The highest skin dose was recorded for the lateral lumbar spine projection while the highest effective dose was measured for AP lumbar spine projection. Conclusion: The ESD’s in this study were much lower than previously reported values. However the effective doses were generally similar and compare well with previous studies. On the basis of the results it can be concluded that the effective dose is a better dosimetry quantity than ESD to determine deterministic effects of radiation.