Abstract:
Introduction: The computed tomography (CT) is identified as the highest contributor of the population
radiation dose among medical radiation examinations. Therefore, routine monitoring of the delivered
radiation dose is critical. The Diagnostic Reference Levels (DRL) are identified as a form of investigation
level that can be used as a tool in identifying the abnormally high radiation doses which cannot be
justified based on the image quality requirements. Therefore, many countries now attempt to define their
own DRL which reflect their own practice. However, to date no formal effort has been taken in
establishing a National DRL (NDRL). Therefore, the present study is aimed to establish NDRLs for
commonly performed CT examinations which include brain, chest and abdomen.
Methodology: A nationwide survey was conducted covering more than 40% (25 CT units) of the CT
units in the country. The patient morphometric (age and gender) together with dosimetric data (Volume
CT dose index: CTDI vol and dose length product: DLP) were recorded for non-contrast studies of head,
chest and abdomen regions belonging to 2982 patients. The median doses for each CT units were
calculated initially and the third quartile of the distribution of the medians were considered as the NDRL.
The obtained NDRLs were compared with the internationally published NDRLs of Japan, Canada and
France to determine the degree of optimization requirements.
Results and Discussion: The NDRLs based on CTDI vol and DLP for head, chest and abdomen regions
were 82.2 mGy/1556 mGy.cm, 7.4 mGy/350 mGy.cm and 10.5 mGy/721 mGy.cm respectively.
Conclusion: The majority of the NDRLs were well below the internationally published values. However,
further dose reductions can be achieved through implementing dose optimization strategies.
