ABDOMINAL EXAMINATION IN KNH USING 16 MULTI-SLICE CT SCAN: REVIEW OF ALARA PRACTICE IN MANAGING PATIENT DOSE

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Objective of the study: To assess the justification of abdominal CT examinations carried out, quantify radiation dose and evaluate the optimization of scanning parameters that contribute to radiation dose determination within the ALARA principle in comparison to international standards.

Methodology:
Through cross-sectional study, 76 patients aged between 20 and 65 years of age, who were referred for abdominal CT scanning at KNH’s department of Diagnostic Radiology were recruited through random sampling between July 2008 and March 2009. Justification of the CT examinations was studied through perusing the request forms from clinicians for the patients that were being scanned to establish how specific the indications were. The CT diagnostic findings were also analyzed in view of how they offered clinical solutions to the requesting clinician. Association between the specificity of the indication and the CT result was also studied. Dose quantification was done through estimation of effective dose, E calculated from the dose length product (DLP) displayed on the console during scanning. Optimization was studied by analyzing the matching of scan protocol with the clinical indication and evaluation of the operator control of scan parameters during the image acquisition process. Patient descriptors including the  transverse abdominal width and scanning protocol practices were also interrogated as possible contributors to this
relatively high dose. Data collection was through a structured table and management was done using Epi Info, SPSS and MS-Excel software.

Results : 18.4% of the examinations had a non-specific clinical indication and 26.3% of the CT findings did not  support a clinical diagnosis. The average E was five times higher than internationally published guidelines for abdominal scanning and within epidemiological concerns. 39.5% of the examinations were done with mismatched  protocols. Specificity of the request and correct protocol matching were positively associated with supporting CT result to the clinical indication.

Conclusion: MDCT as a new and useful technology in medical imaging is providing technical challenges to end users that compromise optimization in reducing patient dose, from Kenyatta National Hospital’s experience. Local protocol practice was shown not only to have had an impact on the dose but also to have influenced the diagnostic yield of
the examinations. Further Quality Assurance practices are needed. This highlighted the fact that in regard to dose reduction, justification for the examination appears to be the main component of ALARA that clinicians and  radiologists can take advantage of