DOSAGE FORMS AND STRENGTHS Initial U.S. Approval: 2007 aHUS Dosage
AP002 CT Head Dosage Comparison Between … Lifelong Learning...CT Head Dosage: Comparison between...
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Department Clinical Audit Project
CT Head Dosage: Comparison between Scanners and Sites
Bernice Lau Derek Emery
Edmonton, Canada
Disclosure Statement
I have no conflicts of interest to disclose ( i.e. no industry funding received or other commercial rela:onships).
Background
• Computed tomography (CT) contributes a major por:on of ionizing radia:on in medical imaging
• CT head examina:ons are typically the first imaging study for a pa:ent with central neurological symptoms
• Differences between scanner manufacturers and specifica:ons will lead to varying algorithms to achieve a diagnos:c study for interpreta:on
International Commission on Radiological Protection 1996
CT dosage metrics • CT dose index (CTDI) used as a metric to quan:fy radia:on output from a CT exam that consists of mul:ple con:guous CT slices
• Reflects average exposure from a single CT slice to a standardized acrylic phantom, taking into account beam width
• Standardized phantoms allow for comparison of exposure between scanners, but do not necessarily accurately es:mate effec:ve dose
• Image quality is also not taken into account McCollough. Radiology 2011; 259:311-6
Diagnos:c Reference Levels
• CT dose metrics provide reference levels to trigger review processes for imaging algorithms
• Diagnos:c reference level is set at the 75th percen:le of dose distribu:on from a survey conducted across a broad user base
CT Head Reference Level (mGy)
Pass/Fail Criteria (mGy)
ACR (2008) 75 80 UK (2003) 65-‐100 EC (2004) 60
American College of Radiology 2002 (rev 2008); Shrimpton and Bongartz, European Guidelines for Multislice Computed Tomography 2004
Aim
• Assess CT dosage metrics for the CT scanners at the University of Alberta (UAH), Royal Alexandra Hospital (RAH), and Sturgeon Community Hospital (SCH) for adult unenhanced head CT scans
• Target is for 100% of CTDIvol for each scanner to be lower than the ACR pass/fail criteria, 80 mGy
Methodology
• Adult (>17 yo) unenhanced CT head examina:ons
• CTDIvol values, scanner and study algorithm (axial vs. helical) collected from PACS retrospec:vely
• 7 consecu:ve working days (Jan 3-‐11, 2012)
Results: UAH
Scanner Axial Helical
# of Scans
# of scans > 80 mGy
# of Scans
# of scans > 80 mGy
128-‐slice
186 0 22 0
dual source 128-‐slice 27 0 1 0
64-‐slice
42 0 3 0
✔
✔
✔
✔
✔
✔
Ac:on Plan
• Target met for all scanners – no further ac:on needed at UAH
Results: RAH
Scanner Axial Helical
# of Scans
# of scans > 80 mGy
# of Scans
# of scans > 80 mGy
16-‐slice
199 0 4 0
dual source 64-‐slice 3 0 0 -‐
320-slice
0 -‐ 86 86
✔
✔
✔
✖
Ac:on Plan
• Target met for 2 RAH CT scanners – no further ac:on needed
• Target not met for the 320-‐slice RAH CT scanner – Results presented to radiologists at RAH – Radiologists collaborated with CT scanner technical specialists to adjust CT head algorithms
– Re-‐audit of 320-‐slice CT scanner in 6 months
Results: SCH
Scanner Helical
# of Scans
# of scans > 80 mGy
320-slice 115 115
• All scans were performed helically, using automa:c exposure correc:on (AEC)
✖
Ac:on Plan
• Target not met for the SCH CT scanner – Results presented to radiologists at SCH – Radiologists collaborated with CT scanner technical specialists to adjust CT head algorithms
– Re-‐audit in 6 months
Re-‐Audit Results
Scanner Helical
# of Scans # of scans > 80 mGy
RAH 320-slice
55 0
SCH 320-slice
92 2
✔
✖
Ac:on Plan
• Target met for RAH CT scanner – no further ac:on needed
• Target not met for the SCH CT scanner – Re-‐present results to radiologists at SCH
Audit Lessons
• Recently installed CT scanners will have algorithms tailored to site specific needs for image quality, but those algorithms may not be designed to meet ACR dose pass/fail criteria
• Audit can assist in reviewing the es:mated CT dose for these scanners