Implementation of an audit and dose reduction program for ct matyagin

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Implementation of an audit and dose reduction program for ct matyagin

  1. 1. Implementation of an Audit and Dose Reduction Program for CT Y. Matyagin and P.J. Collins Department of Nuclear Medicine, PET and Bone Densitometry Royal Adelaide Hospital
  2. 2. CT exposure  Increasing concern worldwide regarding the relatively high level of CT radiation exposure  National Council on Radiation Protection and Measurements: US average dose from medical procedures increased 6x between 1980 and 2007  60% due to CT F.A Mettler Jr., et al. Radiology 2009 Nov;253(2):520-31.
  3. 3. CT exposure  CT now constitutes:  15% of total number of radiological imaging procedures  50% of population’s medical radiation exposure  25% of total radiation exposure F.A. Mettler Jr., et al Health Phys. 95(5), 502-507 (2008).
  4. 4. Radiation induced health risk  A 2009 study estimates (using LNT model) 29,000 cases of cancer could be due to CT scans that were performed in USA during 2007  There is potential for significant dose reduction in many studies as part of an image/dose optimization process B.A. de Gonzales, et al. Arch Intern Med 2009 Dec 14;169(22):2071-7.
  5. 5. Spiral CT CT machine Motorized table Rotating X-ray detectors X-ray beam Rotating X-ray source
  6. 6. Weighted Computed Tomography Dose Index (CTDIw) http://www.impactscan.org/slides/impactcourse/principles%20of%20ct%20dosimetry/index.html • Weighted CTDI represents the average dose in scan plane of Perspex phantom • CTDIW = 1/3 CTDICentre + 2/3 CTDIPeriphery • Phantom diameter: 32 cm or 16 cm • Units: mGy
  7. 7. Volume CTDI (CTDIvol)  CTDIvol: average dose over scanned volume  CTDIvol: accounts for non-contiguous exposure along z-axis  CTDIvol = CTDIw / pitch Pitch 1.5 Pitch 1.0 Pitch 0.75
  8. 8. Dose-length product (DLP)  Total dose: CTDIvol integrated along the scan length, ie.  DLP = CTDIvol • L (where L = scan length)  Units: mGy • cm
  9. 9.  Different tissues of the body have different radiosensitivity  Unit of Effective dose (E) is the Sievert where wT = weighting factor for organ, or tissue T HT = equivalent dose to organ/tissue Effective dose E w HT T T  
  10. 10. Automatic Exposure Control (AEC)
  11. 11. Aim  Compare CT doses (adults) at RAH with an International benchmark  Modify protocol settings to optimize dose/image quality
  12. 12. Dose reference levels  RANZCR have adopted EC1999 values  European Guidelines (EC 2004) were used in this study  Address multi-slice scanners  Includes data from 8 countries EC 2004. G. Bongartz, et al. European Guidelines for Multislice Computed Tomography. FIGM-CT2000-20078-CT-TIP. March 2004
  13. 13. Methods  CT configured to display relevant dose information (CTDIvol, DLP etc.) in PACS  Baseline audit performed  CT scanner exposure settings were reduced in step-wise fashion so as not to compromise image quality
  14. 14. Results CT Doses (% of EC2004) Siemens "Somatom Definition AS+" and Toshiba "Aquilion 16"
  15. 15. Brain perfusion  Major International concern regarding brain perfusion CT  Cedars-Sinai Medical Center in USA:  excessive CT doses in 250 patients  Some studies 8 times expected level  FDA reported significant CT overexposure at several other medical centers in 2009
  16. 16. Brain perfusion overdose Hair loss in patients who received radiation overdoses W. Bogdanich, New York Times, July 31, 2010
  17. 17. Discussion CT Doses (% of EC2004) Siemens "Somatom Definition AS+" and Toshiba "Aquilion 16"
  18. 18. CT Doses (% of EC2004) Siemens "Somatom Definition AS+" and Toshiba "Aquilion 16" Discussion
  19. 19. CT Doses (% of EC2004) Siemens "Somatom Definition AS+" and Toshiba "Aquilion 16" Discussion
  20. 20. CT Doses (% of EC2004) Siemens "Somatom Definition AS+" and Toshiba "Aquilion 16" Discussion
  21. 21. Dose parameters - PACS Store in separate dose information page:  CTDIvol  DLP  Dose/image quality reference settings  Scan time  Patient’s size information
  22. 22. Toshiba dose page 1
  23. 23. Toshiba dose page 2
  24. 24. Siemens dose page
  25. 25. Automatic exposure control (AEC)  AEC switched on  Dose references level set  Effect of other CT parameters on functioning of AEC evaluated  Min and max tube current  Tube voltage  Beam collimation and reconstructed slice thickness  Image reconstruction filters and algorithms
  26. 26. Large/small patients A separate protocol should be employed:  Higher tube voltages for large and (possibly) lower tube voltages for small patients  Rotation time and pitch adjusted to ensure tube current is within acceptable limits  Somewhat higher image noise is acceptable for large patients
  27. 27. Future work  More detailed analysis of image quality  eg. using phantoms  Investigate other key parameters  Slice thickness  Inter-slice intervals  Streak artefacts
  28. 28. Acknowledgement  Radiology Department  George Kourlis (CT senior)

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