Document Type: Original Paper
Department of Medical Physics
Sefako Makgatho Health Sciences University
Introduction: Head scans are the most performed computed tomography (CT) examinations worldwide. However, there are concerns over the probability of increased cancer risks among the exposed populations. Diagnostic reference levels (DRLs) were proposed as a tool for identification of CT doses considered not ideal for the clinical objective. The aim of the study was to establish diagnostic reference levels for the CT head procedures and to estimate the effective dose.
Methods: The dose absorbed by the head slice of a Rando Alderson phantom was measured using calibrated Lithium fluoride thermoluminescent dosimeters (TLDs) while exposed to a CT scanner operated on clinical parameters. Measurements were effected at the peripheral and centre of the slice, measurements were repeated three times each with a set of new TLDs. The doses absorbed by the TLDs were read using a Harshaw TLD Model 5500. The measured doses were used to calculate the weighted CT dose Index (CTDIw ), CT dose index volume (CTDIv ) and the dose length product (DLP). Lastly the effective dose was calculated using the formulae, ED = k × DLP where k = 0.0021.
Results: 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. The ED was 2.1 mSv. These values compared well with some international values.
Conclusion: The established CTDIv, DLP and effective dose for head scan compared well with some international values except in cases where different scan lengths and scanner algorithms were used.