Evaluation of factors affecting the exposure indicator of computed radiography and how it relates to radiation organ dose at a second level hospital in Zambia.

REC Approval Reference No: CPUT/HW-REC 2019/H120The main purpose of conducting this research study was to evaluate if there was any significance in the difference between the Exposure Index (EI) of the postero-anterior (PA) chest, antero-posterior (AP) pelvis and lateral lumbar spine views obtained with a Computed Radiography (CR) system for patients referred for conventional diagnostic imaging and the manufacturer’s standard/recommended EI. Secondly the factors affecting EI in the application of CR at a second level hospital in Zambia were also explored, and lastly, to understand the relationship that exists between EIs and radiation dose imparted to the patient.In order to record the required data for the PA chest, AP pelvis and lateral lumbar spine, radiographers had to complete a data collection form which was designed by the researcher to establish how individual radiographers used parameters of the CR imaging system under study. Completion of the data collection form involved entering of data under each column by hand and determining optimum exposure factors and associated EI generated by radiographers.The data collection form was completed by all the participating radiographers where each was assigned a separate form to complete. The completed forms were collected immediately by the researcher and kept securely in the researcher’s office within the radiology department. The data collection form consisted of 15 variables organised around the following headings:i. Patient details included study number, age and gender.ii. Part to be examined which included PA chest, AP Pelvis and lateral lumbar spine.iii. kVp recorded the voltage used for each specific examination.iv. mAs recorded the ‘current’ used for each specific examination.v. FSD (cm) recorded the distance between the X-ray tube focus and the subject.vi. SDD (cm) recorded the distance between the source (focus) and the IP.vii. Field size (cm) recorded the field on the patient which was being exposed to radiation.viii. Anode angle which recorded the angle the target surface of the anode sits at in relation to the vertical. The X-ray unit used in this study had an anode angle of 14º.ix. Filtration: This entails recording the filtration applied for each examination. The X-ray unit used for this study had a permanent filtration of 0.9Al/75.x. Date of examination recorded whether it was Monday - Friday, weekend or on a public holiday.xi. Time of examination recorded whether the time of the examination fell within normal working hours (Monday-Friday 8am – 4pm) or outside working hours (Monday-Friday 4pm – 8am, weekend and public holiday).xii. Height (cm): The height of the patient was recorded.xiii. Weight (kg): The weight of the patient was recorded.xiv. Type of exposure: There was an option of Auto/Manual. The unit used for this study had manual type of exposure.xv. EI: This involved recording the EI generated by the unit for each image processed in this study. This was important since this study explored the optimisation of the EI as a dose-management strategy.Patient dose assessment was done by comparing the radiographer generated EIs for the PA chest, AP pelvis and lateral lumbar spine to those of the manufacturer. To achieve this, and with the help of the statistician, the Monte Carlo formula was used to calculate effective radiation dose for each examination/patient. The kVp, mAs, FSD, SID, Field size, anode angle, filtration, EI, height and weight for each of the PA chest, AP pelvis and lateral lumbar spine examinations done, were computed using the Monte Carlo software. The Monte Carlo computation generated the effective dose.