Assessment of quality assurance compliance in the use of computed tomography machines in Kenyan hospitals

Abstract

A total of eighteen Computed Tomography (CT) scanners at different hospitals in Kenya were surveyed to assess the state of quality management, image quality and patient dose. This study was conducted between the months of March and August 2005 and as at this time only 21 CT facilities were available in the country. It was estimated that the number of CT examinations in Kenya were 56%, 11%, 13%, 9% and 11% for brain, chest, abdomen, pelvis and other examinations, respectively. It was found that approximately one in every 700 people undergoes a CT examination annually in the country. This study used objective physical parameter measurements from American Association of Physicists in Medicine (AAPM) water phantom to determine image quality from the CT scanners. The quality assurance compliance showed that four (22%) of the CT scanners scored above 75% of a twenty-eight points' scale of both CT performance and patient dose tests. The dose quantities obtained using typical exposure parameters in the head and the body phantoms were compared with the International Commission of Radiological Protection (ICRP) and International Atomic Energy Agency (IAEA) Dose Reference Levels (DRLs). The effective dose obtained showed that the potential optimisation achievable is between 33% and 71%. These high doses in CT procedures require urgent safety measures so as to improve the radiological protection of the patient, workers and the public. Ranges of weighted Computed Tomography Dose Index (CTDIw), MUltiple Scan Average Dose (MSAD), Dose-length product (DLP) and effective dose (E) for the four types of CT examinations considered were respectively as follows; 14 - 96 mGy, 15 - 97 mGy, 430 - 2840 mGy.cm and 1 - 6.53 mSv in the brain, 7 - 28 mGy, 6 - 38 mGy, 238 - 1104 mGy.cm and 4 - 18.77 mSv in the chest, 10 - 44 mGy, 12 - 59 mGy, 342 - 2242 mGy.cm and 5 - 33.63 mSv in the abdomen and 11 - 36 mGy, 14 - 44 mGy, 326 - 1820 mGy.cm and 6.19 - 34.58 mSv in the pelvis. CTDIw values in most hospitals were compliant with DRL while DLP, MSAD and E were mostly non compliant with the DRL. This was mainly influenced by the scanning protocol and device performance. The third quartile effective dose results obtained for the chest examination with the optimally performing CT scanners (33%) showed optimal performance at 47% below ICRP DRL. Further investigation of device performance, optimization and review of the practice is required.