Assessment of Radiological Patient Exposure for Computed Tomography Scanning Examinations - a Case Study at the Nairobi Hospital, Kenya

Abstract

The Nairobi Hospital is recognised in the region as an advanced diagnostic, treatment, and referral centre in medical expertise and services. The hospital has a Brilliance 64-slice CT scanner with an estimated diagnostic output of approximately 3000 to 5000 scans per annum. This research investigation was conducted on available records of all patients to identify radiation protection dosimetry for the optimization of patient-specific CT protocols. A total of two hundred and fifteen CT scans examined were distributed as follows; head with no contrast, head with contrast, chest non-contrast, chest contrast, neck non-contrast, abdomen non-contrast, abdomen contrast, cervical spine non-contrast, cervical spine contrast, lumbar spine contrast, angiography, angiography non-contrast, and paranasal sinuses. The record of the age distribution of patients was 13 to 87 years, 113 female and 102 male patients. An areal background radiation measurement of the CT facility room was performed using a RAD 60TM dosimeter. The radiation dose exposure rate values measured at various localities varied from 0.01 to 0.20 μSv/hr and were within the 0.25 μSv/hr ICRP limits. Quality assurance of the 64- slice CT Scanner was assessed for radiological compliance with 60601-2-44 standard by the International Electro-Technical Commission using 2-part PMMA Phantoms for Computed Tomography Dose Index measurements. For the QA/QC of the CT scanner, there was an observable significant difference (> ± 20%) in all CT practices, between the certified CTDIvol and measured and for both the abdomen and head examinations. The CTDIw values obtained from measurements with anthropomorphic phantoms for both head (92.04 ± 0.08) mGy and abdomen (52.89 ± 0.7) mGy examination protocols, were above EC values; 60 mGy and 35 mGy, respectively. Seventy-two out of 215 patients underwent two or more CT scans, and the cumulative effective dose values for patients with repeated examinations ranged between 3.68 to 83.48 mSv, representing an overall increase by factors 2 to 3. The results for the 75th percentile of the Dose Length Product values for head non-contrast (1134.72 vs. 1050 mGy.cm), abdomen with contrast (2865.4 vs. 800 mGy.cm), and chest non-contrast (773.7 vs. 650 mGy.cm) were all higher than the European Commission guidelines. In conclusion, there is a need for re-evaluation for optimizations of various CT examinations, to obtain genderspecific protocols, to reduce exposure levels to an achievable level following the International Commission on Radiological Protection publications 60 and 87