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Patient-dose audit and subsequent optimisation of CT aortic angiograms
EP23349
Poster Title: Patient-dose audit and subsequent optimisation of CT aortic angiograms
Submitted on 09 Sep 2015
Author(s): Mr David J Platten (1), Dr Davis V Thomas (2)
Affiliations: 1. Medical Physics Department, 2. Department of Radiology, Northampton General Hospital, United Kingdom
Poster Views: 1,695
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Poster Information
Abstract: Audit showed that doses for CT Aortic Angiograms (CTAA) were above the recommended national reference dose (NRD). This group of patients was looked at in more detail, which showed the dose was within the NRD. Nevertheless, changes were made to reduce cumulative doses.

Study information was exported from OpenREM for adult studies carried out using a Siemens Definition AS scanner between June and August 2014. The mean DLP for CTAA was 1170 mGy.cm (n=45), exceeding the NRD (1040 mGy.cm). A larger number of studies was analysed in more detail (n=70). Each was reviewed: scans that included the peripheral run-off or thoracic aorta were excluded. Patients with a diameter larger than 500 mm were also excluded.

The mean DLP of the filtered dataset was 1180 mGy.cm (n=64). However, due to the skewness of the dose distribution, the median (1030 mGy.cm) was used. This is comparable with the NRD (1040 mGy.cm) and therefore acceptable.

The CTAA scan protocol was examined with a view to optimise cumulative dose. The patient group is typically men between the ages of 60-80 with abdominal aortic aneurysms (AAA). AAA is usually treated using endovascular stent-graft insertion (EVAR), necessitating up to three follow-up CTA scans in the first year.

The existing scanning protocol involved pre- and post-contrast acquisitions from diaphragm to groins. We concluded that the pre-contrast acquisition was required on the initial study but not at follow-up, thereby reducing dose by 50% for each follow-up scan and the cumulative dose in the first year by up to 37%. A follow-up re-audit is planned after one year to confirm our estimates and re-evaluate practice.
Summary: The results of a routine CT patient dose audit prompted a review of the CT Aortic Angiogram scanning protocol. The pre-contrast helical acquisition has been removed from follow-up CTA studies. An estimated saving of 500 mGy.cm will be made per follow-up study. Assuming up to three follow-up CTAs in the first year, this represents a cumulative dose reduction of up to 37 % compared with previous practice.References: 1. “PHE-CRCE 013: Doses from computed tomography (CT) examinations in the UK (2011 review)”, Public Health England, September 2014.
2. http://www.openrem.org
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