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Review of Recent CT Accidents: Dosimetry, Risk Analysis, and Lessons Learned

Review of Recent CT Accidents: Dosimetry, Risk Analysis, and Lessons Learned. NC HPS SPRING MEETING MARCH 4-5, 2010 RALEIGH, NC. Terry Yoshizumi , PhD*, David Enterline , MD Greta Toncheva , MS Duke University Medical Center Durham, NC. ACKNOWLEDGEMENTS. Robert Reiman, MD

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Review of Recent CT Accidents: Dosimetry, Risk Analysis, and Lessons Learned

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  1. Review of Recent CT Accidents:Dosimetry, Risk Analysis, and Lessons Learned NC HPS SPRING MEETING MARCH 4-5, 2010 RALEIGH, NC Terry Yoshizumi, PhD*, David Enterline, MD Greta Toncheva, MS Duke University Medical Center Durham, NC

  2. ACKNOWLEDGEMENTS • Robert Reiman, MD • Don Frush, MD • Ehsan Samei, PhD • James Colsher, PhD

  3. TOPICS • Review of recent CT accidents • What is CT perfusion (CTP)? • Why is the dose so large? • How do we measure organ doses? • Results of Cedars-Sinai’s protocols • Risks identified • Scrutiny began at federal level • Lessons learned • Concluding remarks

  4. Review of Recent CT Accidents 2005 2008 2009 EurRadiol (2005) 15:41-46 Hair loss: 3 cases CTP + angiography study 2 1/2 yr old 151 scans in period of 65 minutes (CBS13.com) FDA Warning 10-8-09 Cedars-Sinai, CTP 206 pts over 18-mo. 3-4 Gy (normal 0.5 Gy) 80 hair loss 56 direct exposure to lens of the eye + 50 identified from other states (FDA Report)

  5. Brain CT Perfusion ImagingClinical Applications • Stroke and Ischemia • Diamox Challenge • Vasospasm • Tumor evaluation • CTP and CT permeability

  6. 0.14 0.12 Area 0.10 0.08 0.06 0.04 0.02 0.0 -0.02 0.14 0.12 Volume 0.10 0.08 Mean transit time 0.06 0.04 0.02 0.0 -0.02 Analysis of time-concentration curves Tracer Kinetic Theory Area under concentration curve Volume = MTT Flow =

  7. 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.0 -0.02 Perfusion Imaging CBV • CT: Conc = k (density) CBF Time Concentration Curve MTT

  8. Choosing Arterial Input Funct (AIF) & Venous Output F (VOF) VOF AIF

  9. Compensated ischemia of LICA Increased CBV (green) due to autoregulation MTT CBF CBV Prolonged MTT (red) Low CBF (blue)

  10. Compensated ischemia of LICA MTT CBF CBV Normal: 3-5 sec > 40 mL/min/100 g brain ~3

  11. Borderline CBF With Low CBV Predicts Infarction (No Intervention) infarct CBV - 5 hours T2WI - 24 hours (MRI)

  12. CT Perfusion- Absolute and Relative CBF Analysis • Absolute CBF of 10-20 ml/100g/min represents ischemic tissue but viability depends on duration of ischemia • When ischemia is associated with an area of core infarct, this represents the penumbra • Decreased CBV with compromised CBF implies infarction

  13. CT Perfusion • CINE mode: • 80 kVp, 200 mA, 1 sec • Repeat 45 sec • Table fixed

  14. WHEN THE DOSE BECOMES AN ISSUE IN CTP When human errors introduced – scan parameters altered, i.e., the energy changed from 80 kVp to 120 kVp, or tube current (mA) modulation used without understanding consequences Why: Display constantly updated images by continuous rotation of the tube at the same location; potential for high dose at the level of scan

  15. How do we measure organ doses? • Manual Look-up tables (Outdated) • Organ dose from CTDI (No value, but CTDI is useful for monitoring dose) • Monte Carlo based dose calculator (complex, time consuming) • Effective Dose from DLP (No value) • Anthropomorphic phantom with TLDs (Labor intensive) • Anthropomorphic phantom with MOSFET(metal oxide semiconductor field effect transistor) detectors (Best value)

  16. Materials and Methods • Patient Dose Verification System AutoSense, Model TN-RD-60 • Radiation detectors: 20 Metal Oxide Field Effect Semiconductor Transistors (MOSFET), Model TN-1002RD, High sensitivity Reader, Model TN-RD-15 Bias supply, Model TN-RD -22 AutoSense PC Software, TN-RD-45 • MOSFET dosimeter: Silicon chip 1mm2 Active area 0.2mm x 0.2mm MOSFET AUTO-SENSE SYSTEM MOSFET

  17. Adult Male Phantom Tissue Equivalent Anthropomorphic Phantom Model 701-D Steven SN : 701-285 39 slabs Height -173 cm, Weight - 73 kg Thorax Dimensions: 23 x 32 cm Head: AP 21cm, Lateral 17.1cm Neck at the thyroid: AP 13 cm, Lateral 14.6 cm CIRS www.cirsinc.com

  18. A FEW WORDS ABOUT THE ED AND WEIGHTING FACTORS

  19. CONCEPT OF EFFECTIVE DOSE EQUIVALENT OR EFFECTIVE DOSE • ICRP Report 60 (1990) • Equivalent Dose • Radiation Weighting Factor • Tissue Weighting Factor • Effective Dose • ICRP 103 (2007) • Equivalent Dose • Radiation Weighting Factor • Tissue Weighting Factor • Effective Dose • ICRP Report 26 (1977) • Dose Equivalent • Quality Factor • Weighting Factor • Effective Dose Equivalent

  20. WT : ICRP 26 (1976), ICRP 60 (1990), ICRP 103 (2007)

  21. ICRP 103 Weighting Factors

  22. Notes on Effective Dose Calculations • Skin Dose: taken the highest of the anterior and posterior, the posterior skin dose is reduced due to attenuation by the table • Brain Dose: the dose is averaged from the dose of all brain locations • Bone marrow: the dose is a sum of the measured bone marrow dose at different locations multiplied by the % distribution • Lens of the eye: average of the two • Bone surface: the measured dose is adjusted with the dry bone f-factor (different for soft tissue and bone), f-factor is the conversion from R to cGy, at different tissues and energies used during the MOSFET calibrations • All protocols were measured three times and the averaged value was used • Misc.: in occasions where out of three measurements two are “0”, only the one number was used, or if there was one “0” and two numbers, the average of the only two was used • The new ICRP 103 was used with the new weight factors (listed in the next slide)

  23. ADULT CTP FDA 0.5 Gy

  24. TUBE CURRENT MODULATION • Basic Concept: • Adjust the tube current to accommodate the patient contour and composition

  25. TUBE CURRENT MODULATION mA2 mA1 mA1 mA2 modulation around the z-axis modulation around the cross-section mA2 mA1 modulation – axial and helical

  26. Fixed mA 100% Z Modulation - Auto mA 55% XYZ Modulation 40% mAs How smart mA works • Projection data from a scout scan measures the patient and determines how to modulate the mA for improve dose efficiency and consistent IQ CHEST ABDOMEN PELVIS Jim Colsher, GE Healthcare

  27. An AutomA Example (Noise Index =24) sd 25.4 sd 23.7 sd 22.6 GE Healthcare

  28. Results: Effective Dose ED (Adult), excerpt from NCRP 160, 2009

  29. Results: Organ doses

  30. Results: Lens of the Eye

  31. Results: Skin Dose

  32. Brain Dose

  33. Risks identified from CTP

  34. FDA Report (10-7-09)http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?MDRFOI__ID=1495886 (GE Version) SUMMARY: • No malfunction on the scanner • Protocol altered by the site user

  35. Recommendations from FDA • Check for excess radiation from CT Perfusion • Review radiation dosing protocols for all CT perfusion studies • Implement quality control procedures • Check the CT scanner display panel before performing a study to make sure the amount of radiation to be delivered is at the appropriate level for the individual patient. • For multiple scans on a patient during one imaging session, practitioners should adjust the dose of radiation

  36. Lessons learned • Need for quality assurance of protocol development/modification including dosimetry oversight • Need for team approach in dealing with patient safety • Need for radiation safety education for all personnel involved • Need for institutional oversight by the Radiation Safety Committee

  37. Concluding remarks Key questions to ask regarding Cedars-Sinai incident? • Was it machine failure? • Was it human failure? • Wrong scan protocols implemented – no one challenged changing 80 kVp to 120 kVp, or use of Auto mA mode with low noise factor • Failure by the technologists, radiologists and physicist • What signs were there? • High CTDI values missed. You must look for it! • What was the protocol review process?

  38. Concluding Remarks CONGRESSIONAL HEARING OCCURRED (F-2-26-2010). This may be the beginning of a new period for radiation protection.

  39. Concluding remarks WHAT WAS LOST IN ALL THESE HYPE? • Cold Facts on Stroke • The third leading cause of death in the US • The leading cause of adult disability • Every year about 750,000 Americans experience stroke and about 160,000 (21%) die from it • Fundamental issue: Over-radiation without oversight • CTP is a valid protocol that uses 0.5-0.8 Gy , but should be < 1Gy Live/die vs. Hair Loss WHICH WOULD YOU CHOOSE?

  40. THANK YOU.

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