Sean Cournane MSc, PhD, Presenter: Nothing to Disclose

Dara Murphy, Abstract Co-Author: Nothing to Disclose

Michael Rowan BSC,MSc, Abstract Co-Author: Nothing to Disclose

Una O' Connor, Abstract Co-Author: Nothing to Disclose

David P. Costello MSc, BSC, Abstract Co-Author: Nothing to Disclose

Niall Sheehy MBBS, Abstract Co-Author: Nothing to Disclose

Neil O'Hare, Abstract Co-Author: Nothing to Disclose

This study presents the establishment of appropriate adult diameter-based local and national DRLs, in order to comprehensively represent the size range of the examined population. 

Diagnostic Reference Levels (DRLs) provide an investigative level to identify unusually high patient doses. CT adult DRLs are currently calculated as the 75th percentile of exam specific CTDIvol and DLP datasets for adult patient samples of weight range 60-80kg and typically based on small samples of 10 or more. While DRLs provide a practical metric for ‘normal’ adult patients, these investigative levels if used for the broad size range of all patients may prove inappropriate. Further, it is well known that body weight is poorly correlated with CT dose metrics, prompting the question as to whether DRLs in their current form are fit for representing the entire adult population. Size-specific reference doses have been suggested for paediatric patients; however, such analyses have not been performed in adults. Accordingly, the object of this work was to propose diameter-based local and national DRLs and to examine the variability of diameter-specific metrics across examinations and hospitals sites.

Dose metric data from 19 CT scanners across the Irish National Integrated Medical Imaging System (NIMIS), for all examinations (n=149784), was captured by Radimetrics eXposureTM software over an 18-month period, allowing for the collation of CT scanning parameters including CTDIvol, DLP, Size-Specific Dose Estimate (SSDE) and effective patient diameter. After data clensing, diameter-specific 25th, 50th and 75th parameter percentiles were calculated to inform on establishing local and national DRLs with high volume, high dose and newly established CT exams investigated.

For patients of increased diameter, elevated 75th percentiles were evident when compared with normal-sized patient levels, suggesting traditional DRLs to be ineffective at flagging higher dose investigative levels for all patients. The work also allowed for the comparison of examination- and size-based CT dose metrics for systems of similar model and manufacturer, in addition to across a range of manufacturers.  

Cournane, S, Murphy, D, Rowan, M, O' Connor, U, Costello, D, Sheehy, N, O'Hare, N, Patient-diameter Specific Local and National DRLs for Adult Body CT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14012942.html