Establishment of Diagnostic Reference Levels and Estimation of Effective Dose from Computed Tomography Head Scans at a Tertiary Hospital in South Africa

Head scans are the most frequently performed computed tomography (CT) examinations worldwide. However, there is growing concern over the probability of increased cancer risks among the exposed populations. Diagnostic reference levels (DRLs) identify radiation dose that is not commensurate with clinical objectives. The aim of this study was to establish DRLs for CT head procedures and estimate effective dose (ED).
The dose absorbed by the head slice of a Rando Alderson phantom was measured using calibrated lithium fluoride thermoluminescent dosimeters (TLDs) exposed to a CT scanner operated on clinical parameters. The measurements were done at the periphery and center of the slice, and repeated twice with a new set of TLDs. The radiation dose absorbed by the TLDs was read using a Harshaw TLD reader, Model 5500. The measured doses were used to calculate the weighted CT dose index (CTDIw), CT dose index volume (CTDIv), and dose length product (DLP). Finally, the ED was calculated using the formula; ED = k × DLP, where k was considered as 0.0021.
The mean absorbed dose was 30.9 mGy, while the established CTDIv and DLP values for the head protocol were 40 mGy and 990 mGy.cm, respectively. Additionally, the ED was calculated as 2.1 mSv. These values compared well with some international values.
According to the results of the present study, the established CTDIv, DLP, and ED for head scan were well-compared with some international values, except in the cases using different scan lengths and scanner algorithms.