Diagnostic reference levels for computed tomography of the head in Anambra State of Nigeria

Background: Diagnostic reference levels (DRLs) were first conceptualized in 1996 by the International Commission on Radiological Protection as a result of wide variations in patient dose levels for the same examination. Current works on computed tomography (CT) doses in Nigeria produced significant variations. These observed variations, coupled with unavailable national or regional DRLs have presented the need for the establishment of standards through a dose survey. Objective: The aim of this study is to establish DRLs for CT of the head in adult populations of Anambra State of Nigeria. Materials and Methods: The retrospective survey was carried out from February to June 2016 in the four busiest CT centers. The digital CT population considered was those of subjects examined in 2015, and who were aged ≥18 years. Two hundred folders, comprising fifty from each center were included. The on-screen volume computed tomography dose index (CTDI vol ) and dose-length product (DLP) for the subjects were recorded. The 75 th percentile was then calculated for each center to establish center-specific DRLs. Finally, a combined 75 th percentile of the CTDI vol and DLP for all centers was calculated to establish the DRLs for the state. Data were analyzed using SPSS version 20.0 (SPSS Incorporated, Chicago, Illinois, USA). Results: The digital folders of 104 male and 96 female subjects with age range of 18–93 years were analyzed. The specific 75 th percentile of the CTDI vol and the DLP of the centers ranged from 46 to 86 milligray (mGy) and 794 to 1785 mGy centimeters (mGy-cm), respectively. The DRLs for the State are 66 mGy and 1444 mGy-cm, respectively. Conclusion: The DRLs for head CT in Anambra State has been derived. Although the CTDI vol is comparable to the recommendations of the European Commission, the DLP is significantly higher. Further training on dose optimization may help to bring the radiation dose in the locality at par with foreign values.