Diagnostic reference levels for lumbar spine x-ray examinations in eight x-ray health units in Kampala, Uganda

Abstract

Introduction Lumbar spine plain radiography contributes relatively high doses of radiation compared to a chest x-ray; 10mGy for AP and 30mGy for lateral projections according to IAEA and European commission on radiation protection. There is an increase in the number of lumbar spine x-rays as reflected from records at Mulago national referral hospital, where 21% of the X-ray examinations done are lumbar spine (2013) but previously in year 2002 these used to account for 10.5%. The ICRP and the Bonn Call-for-Action Setting the Scene for the Next Decade” in Bonn, Germany, in December 2012, requires the implementation of the principle of optimization of protection and safety by ensuring establishment, use of, and regular update of diagnostic reference levels for radiological procedures. Countries that have developed DRLs have registered a reduction in dose of more than 30%. There are no established DRLs for lumbar spine x-ray examination in Uganda and no prior data has been collected for lumbar spine examination. Objectives To determine the diagnostic reference levels for adult AP and lateral lumbar spine x-ray examination in Kampala, compare the DRLs among the different x-ray units and with the International standard Methodology This was a cross-sectional study involving 8 health x-ray units in Kampala city. X-ray units 1 and 4 were public, 7 was research based, 5and 6 were religious based and 2, 3, and 8 were private for profit. Adult patients presenting at the x-ray units for lumbar spine x-ray examinations were recruited. Systematic sampling was used where every 5th patient in 7 units who met the inclusion criteria and consented was eligible for the study. Every 10th patient was recruited from one unit which received the highest number of patients. The study variables were; Age, Sex, Weight, Focus skin distance, Computer radiography, Digital radiography, Conventional/Analogue, kilo voltage peak kVp, milliampere second mAs, Incident air Kerma, Entrance Skin Dose. Patients’ radiographs were taken with optimal factors were used to obtain quality radiographs. The ESDs were calculated from these factors by calculating the IAK, ESDs and obtaining the 75th percentile of ESDs to give the DRLs. A descriptive statistic data analysis was used; univariate analysis answered objective 1 and 2. ESDs were summarized as means with standard deviations. The 75th percentiles of ESDs gave us the DRL for each unit which we compared. The 75th percentiles were summarized as means to get the local DRL which was compared to the international standards. Results A total of 160 patients undergoing lumbar spine x-rays with a 320 views, anteroposterior and lateral views were studied . The majority of the units 6 (76%) used analogue x-rays, while 12% used CR and 12% used DR radiography. The majority of the patients were female with a female to male ratio of 1.2:1. The patients’ age ranged from 19 to 97 years. The majority of the patients were between the age group of 59-68 years. The mean weight of 71.6 kilograms. The majority of the patients were between 60-89kg. The mean tube voltage for AP was 81.4 kVp. The mean tube current was 35.7 mA. While the mean tube voltage for lateral view was 90.1 kVp and mean tube current 46.61 mAs. The DRL for AP and lateral lumbar spine x-ray examination were 3.7mGy and 6.2mGy respectively. These were lower than those of IAEA (5and 15mGy) and CEC (10 and 30mGy) Conclusion These DRLs for antero-posterior and lateral lumbar spine x-ray examination are 3.7mGy and 6.2mGy respectively, and both of these are lower than those recommended by IAEA and European commission. Recommendation These results are recommended for baseline data in the development of the national DRLs