RADIATION DOSE CONSIDERATIONS IN CT IMAGING

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RADIATION DOSE CONSIDERATIONS IN CT IMAGING

• Jeffrey T. Seabourn, M.D.
• Gem State Radiology

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Disclosures
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Disclosures
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Radiation Dose Considerations in CT
ImagingLearning Objectives

• Learn the reasons for heightened concern about
  radiation exposure from CT
• Learn basic concepts of radiobiology, CT
  radiation measurement, and range of exposures for
  various exams
• Understand the consensus opinions on the risks of
  radiation
• Learn about strategies Radiologists employ to
  minimize radiation exposure from CT

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Radiation Dose Considerations in CT
ImagingLearning Objectives

• Learn the reasons for heightened concern about
  radiation exposure from CT
• Learn basic concepts of radiobiology, CT
  radiation measurement, and range of exposures for
  various exams
• Understand the consensus opinions on the risks of
  radiation
• Learn about strategies Radiologists employ to
  minimize radiation exposure from CT

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Radiation fear Why Now?

• Rapid rise in population radiation exposure from
  medical imaging
• NEJM article 11/07 by Brenner Hall
• Lay press activity USA Today, Time, Washington
  Post, NY Times
• X-rays classified as carcinogens by WHO, CDC, and
  NIEHS

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Radiation exposure from CT

• 60 million CTs/yr in 2006 c/w 3 million in
  1980.
• Estimated at between 69-72 million in 2007.
• 4-7 million CTs performed annually on Peds
• Increasing by 10 per year
• 33 under age 10
• 10 times more sensitive to radiation
• Rate has doubled in last 5 years
• CT has become the largest source of medical
  radiation dose

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Radiation Fear
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Radiation Fear Recent developments

• Radiation over-exposures reported at Cedars-Sinai
  Medical Center involving brain CT perfusion scans
• Prompts FDA investigation 10/09
• Initially reveals 206 cases of over-exposure (8x
  expected level) over an 18 month period.
• FDA finds additional cases in LA area and in
  Alabama
• Class action lawsuit filed

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Radiation Fear Recent developments

• FDA launches initiative to rein in medical
  radiation 2/9/10
• Congressional sub-committee hearings on radiation
  safety 2/26/10
• FDA hearings on radiation safety 3/30/10

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Radiation Fear Recent Publications

• Exposure to Low-Dose Ionizing Radiation from
  Medical Imaging Procedures. NEJM, August 27,
  2009 Number 9 Volume 361849-857 Reza Fazel,
  M.D., et. al.
• Collected CT data from 5 Healthcare markets from
  2005-2007
• Categorized effective radiation doses into 4
  categories
• Low (lt3mSv)
• Moderate (gt3-20mSv) 19.4 of enrollees
• High (gt20-50mSv) 1.9 of enrollees
• Very high (gt50mSv) .19 of enrollees
• Conclusions Imaging procedures are an important
  source of exposure to ionizing radiation and can
  result in high cumulative effective doses

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Radiation Fear Recent Publications

• Projected Cancer Risks From Computed Tomographic
  Scans Performed in the United States in 2007.
  Amy Berrington de González, Dphil et. al.
• Arch Intern Med. 2009169(22)2071-2077.
• Sponsored by NIH and NCI
• Estimated 29,000 new cancers from CTs performed
  in 2007
• Estimates based on BEIR VII risk modeling

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Radiation Fear Recent Publications

• Radiation Dose Associated With Common Computed
  Tomography Examinations and the Associated
  Lifetime Attributable Risk of Cancer. Arch Intern
  Med. 2009169(22)2078-2086. Rebecca
  Smith-Bindman, MD et. al.
• Radiation doses from common CT exams were higher
  and far more variable than previous estimates.
• Up to a 13-fold variation between highest and
  lowest dose for each study type
• Attempted to measure LAR of cancer based on age,
  sex and CT dose estimates.

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Radiation Dose Considerations in CT
ImagingLearning Objectives

• Learn the reasons for heightened concern about
  radiation exposure from CT
• Learn basic concepts of radiobiology, CT
  radiation measurement, and range of exposures for
  various exams
• Understand the consensus opinions on the risks of
  radiation
• Learn about strategies Radiologists employ to
  minimize radiation exposure from CT

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Radiation Bio-effects

• Direct interaction
• Cellular macromolecules (proteins or DNA) are hit
  by ionizing radiation
• Cell death
• DNA mutation
• Indirect interaction
• Radiation interacts with cellular water
• Hydrolysis of H20 resulting in a OH- free radical
• Formation of unstable H2O2 stable organic
  peroxide lack of essential enzyme cell
  death
• Anti-oxidants block recombination into H2O2
  preventing stable organic H2O2 compounds from
  occurring

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Radiation terms and definitions

• Radiation exposure (R) ionization of air by
  photons (x-rays).
• Absorbed dose (Gy) energy absorbed due to
  ionizing radiation.
• Equivalent dose (Sv) takes into account the
  type of radiation involved (gamma vs. x-rays)
• Effective dose (Sv) accounts for tissue
  radiosensitivity in determining equivalent whole
  body dose.

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Organ Radio-sensitivity
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Biological Effects of Ionizing Radiation

• Stochastic Effects
• Deterministic Effects

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Stochastic Effects

• Exposure to low-dose radiation
• Severity is independent of dose
• No safe threshold dose
• Probability of a biological effect increases with
  dose
• May take a lifetime to manifest (or more)
• Results in carcinogenesis and genetic effects

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Deterministic Effects

• Result from high radiation doses
• Generally not an issue in diagnostic imaging
• Severity is dose dependent
• Higher dose increased severity
• There is a threshold
• Examples hair loss, cataracts, skin changes,
  sterility, nausea, CNS damage, death

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Deterministic effect Band alopecia CTA Brain
perfusion
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CT RADIATION MEASUREMENTS CDTI AND DLP

• CTDI CT dose index (mGy)
• DLP Dose length product (mGy-cm)

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CT RADIATION MEASURMENTS CTDI

• CTDI (mGy)
• CTDI100
• CTDIW Weighted avg. of center (1/3) and
  peripheral (2/3) contributions of dose.
• CTDIVOL CTDIW/pitch
• For the same tube current and voltage,
• Decrease in diameter will increase effective
  dose
• Smaller pitch will increase CTDI

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CT RADIATION MEASUREMENTS DLP

• DLP (mGy-cm)
• CTDIVOL x scan length
• Represents the integrated dose across the scan
  length.
• Can be multiplied by a conversion factor to yield
  an effective dose estimate

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CT RADIATION MEASUREMENTS

• CTDIVOL and DLP are displayed on newer CT
  scanners.
• Useful for comparing CT protocols between
  scanners.
• Do NOT represent effective dose measurements
  (mSv).
• Represent calculations from phantom measurements.
• Can be used to estimate effective dose using
  conversion factors.

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ESTIMATING EFFECTIVE DOSE FROM CT

• Effective dose estimates can be calculated using
  anatomic region specific conversion factors and
  multiplying them by the DLP.
• Effective dose (mSv) DLP k(E/DLP)
• Representative adult values for k(E/DLP) are
• Head/Neck .0031
• Head .0021
• Neck .0059
• Chest .014
• A/P .015
• Trunk .015

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Comparison of Adult and Pediatric k-values
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ESTIMATING EFFECTIVE DOSE EXAMPLE ADULT HEAD CT

• Head CT
• CTDIVOL 118.4 mGy
• DLP 1183 mGy-cm
• Effective dose estimate DLP x 0.0021
• 2.5 mSv

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Radiation Dose Considerations in CT
ImagingLearning Objectives

• Learn the reasons for heightened concern about
  radiation exposure from CT
• Learn basic concepts of radiobiology, CT
  radiation measurement, and range of exposures for
  various exams
• Understand the consensus opinions on the risks of
  radiation
• Learn about strategies Radiologists employ to
  minimize radiation exposure from CT

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Risks of Ionizing Radiation from Diagnostic
imaging

• No published studies have directly attributed
  cancer to CT scanning
• Relationship between radiation exposure and
  cancer risk at low radiation doses is less clear
• Proving this definitively and accurately would
  require hundreds of thousands to millions of
  subjects
• Therefore, assumptions must be made based on
  other forms of ionizing radiation exposure
• Most widely used source Atomic bomb survivors
• Additional sources of risk estimates come from
  expert panel reviews
• BEIR reports
• ICRP
• UN Subcommittee on Atomic Radiation

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Atomic Bomb Survivor Data

• Largest longitudinal study to date
• 35,000 survivors exposed to doses lt 150mSv
• Followed for cancer incidence over 55 years
• Direct, statistically significant evidence for
  risk in the dose range from 5-150 mSv
• Instantaneous WB exposure to x-rays, particulate
  radiation, neutrons
• Pierce, DA and Preston, DL. Radiation-related
  cancer risks at low doses among atomic bomb
  survivors. Radiation Research, 200, 154(2) p.
  178-86.

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Radiation Exposure

• Background 3 mSv/ year at sea level
• Transcontinental Flight 1mSv/hour
• Chest X-Ray 0.02 mSv
• MDCT Abdomen and Pelvis 10 mSv
• Hiroshima Survivors showing excess cancer deaths
  2 to 20 mSv

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Radiation Dose Comparisons
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Adults age 45 or older

• Very low risk of excess cancer for one scan
• High prevalence of cancer in patients over 45
• May not live long enough to express mutation
• Usually past reproductive age

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But for a 10 year old

• Long lifespan in which to manifest mutation
• Immature, rapidly developing body systems, more
  radiosensitive
• May pass mutations to progeny

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Compare the Risk
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Compare the Risk
Estimated radiation-induced cancer risk is 3-5
times greater in children than in adults
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Radiation Risk in Context

• Baseline risk of cancer 20-25 (1 in 4-5)
• Late middle aged adult getting average CT has
  lifetime risk of cancer increased from 20 to
  20.01

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Comparable non-radiation risks

• Assume 10 mSv CT scan
• Smoking 140 cigarettes in lifetime (lung CA)
• Spending 7 months in NYC (air pollution- lung CA)
• Driving 4,000 miles in a car (accident)
• Flying 250,000 miles in a jet (accident)

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Risks of Ionizing Radiation from Diagnostic
ImagingBottom Line

• No direct cause-effect relationship established
  between low-dose radiation and cancer
• Although the risk is small, it is also cumulative
• Statistically significant increase in cancer
  risks above 50mSv
• The benefits of an indicated CT far outweigh the
  risks

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Radiation Dose Considerations in CT
ImagingLearning Objectives

• Learn the reasons for heightened concern about
  radiation exposure from CT
• Learn basic concepts of radiobiology, CT
  radiation measurement, and range of exposures for
  various exams
• Understand the consensus opinions on the risks of
  radiation
• Learn about strategies Radiologists employ to
  minimize radiation exposure from CT

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Radiation exposure from CT

• Collective dose to population is rising
• High radiation dose per exam
• Increasing number of indications
• Increasing availability
• Easier to perform
• Faster

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Two Pillars of CT Dose Reduction
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Appropriate Utilization

• Causes of over-utilization
• Defensive medicine practices
• Estimated that up to 30 of imaging is
  unneccessary
• Physician self-referral
• Imaging the worried well
• Inappropriate recommendations for CT imaging by
  Radiologists
• ACR appropriateness criteria
• Whole Body CT screening

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Appropriate Utilization

• Strategies to reduce radiation exposure from CT
  exams
• CT vs. other imaging tests
• Avoid repetitive studies
• Tailor the exam to the patient
• Tailor the exam to the application
• Reduce dose as much as possible
• Limit the scan range

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Appropriate Utilization

• CT should be avoided when an US or MRI is of
  comparable diagnostic utility
• Body MR Liver, Pancreatic, and Renal imaging
• US vs. CT for appendicitis in children
• ACR appropriateness criteria
• US 8/9 RRL none
• CT 7/9 RRL high

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Appropriate Utilization

• CT should be avoided when prior diagnostic
  radiation exposure is excessive
• Repeat visits to ED
• Chest pain CTPA
• Abdominal pain A/P CT

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Optimization of CT protocols

• CT technique should be tailored to the patient
  and his/her body habitus
• Use of pediatric specific imaging protocols
  (Image Gently campaign)
• Reduction of peak KvP relative organ dose
  reductions range from 30-55
• Use of AEC programs
• Patients with a larger body habitus will receive
  a larger dose, but still have issues with image
  noise

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Optimization of CT protocols

• CT technique should be monitored and controlled
  to ensure that the dose is as low as reasonably
  achievable (ALARA principle)
• Peak KvP optimization BMI or weight-based
  protocols
• Tube current adjustment (mAs) AEC software
• Adjust pitch in pitch, decrease in dose
• Develop and use a chart or table of tube-current
  settings based on patient weight or diameter and
  anatomical region of interest.
• Reduce the number of multi-phasic scans with
  contrast
• Limit the scan range

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Sure Exposure Dose Reduction System
After the operator sets plan on scanogram, the
scanner will calculate the absorption of patient
body, and decide appropriate scan technique
. During scanning, the scanner modulates mA with
every gantry rotation. (right)
As a result, detector output is maintained.
Therefore, the image noise of each slice is also
maintained, providing the same Image Quality at a
lower patient dose. (left)
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Future efforts at CT dose reduction

• Hardware improvements from vendors
• Shift away from slice wars with a renewed
  emphasis on dose reduction strategies
• Volume scanning- Aquilion One
• Dual energy- Siemens Definition Flash
• More efficient detectors- GEMS
• Software Iterative reconstruction techniques
• ASIR- GEMS
• IRIS- Siemens

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Technological Advancements in CT Dose Reduction
ASIR
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Future efforts at CT dose reduction Dose
Awareness

• Requirements to list CTDIvol and DLP with the
  patients image data
• Pilot program to integrate patient dose profile
  at order entry level
• Would require the ordering provider to break the
  glass if patient has exceeded agreed upon
  cumulative dose thresholds

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Future efforts at CT dose reduction Dose
Awareness

• Dose Index Registry (DIR)
• Part of National Radiology data Registry (NRDR)
• Will collect and provide feedback on dose
  estimate information from various modalities
• Allows fine tuning of protocols and increases
  awareness

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Future efforts at CT dose reduction Legislative
and Regulatory reform

• Congressional oversight and legislation to reduce
  medical radiation errors
• Intelligently attempt to modify the currently
  fragmented oversight, accreditation, licensing
  and QA requirements for medical use of radiation
• Rep. Waxman astonished that no federal agency
  has authority over medical radiation safety
  issues
• FDA regulations

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What can patients do?

• Keep accurate health records to document exposure
  to ionizing radiation
• Google Health
• EMR patient portals
• Seek out facilities that are committed to
  radiation safety
• ACR accredited facilities
• Independent audit of CT utilization
• Protocols
• Tech training
• Image quality

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What can patients do?

• Ask questions
• Why do I need this exam?
• How will having this exam improve my
  healthcare?
• Do you have an ownership interest in the CT
  scanner?
• Be an advocate for your children
• Is CT the best test for this indication?
• Will the exam be adjusted based on the size of my
  child?

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What Providers can do

• Become dose aware
• Education
• Lectures
• Websites
• www.acr.org
• www.radiologyinfo.org
• www.imagegently.org
• Appropriate utilization
• ACR appropriateness criteria with RRLs
• Utilize Radiologists as a resource

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Physician Education

• Useful websites
• www.acr.org
• Radiation safety
• ACR appropriateness criteria
• www.radiologyinfo.org
• Jointly sponsored by ACR/RSNA
• Information for patients
• www.imagegently.org
• Image gently campaign
• Sponsored by the alliance for Radiation Safety in
  Pediatric Imaging

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What GSR does

• Standardization of CT protocols across facilities
• Reduce dose for or eliminate multi-phasic exams
• Individually protocol every CT exam that gets
  ordered
• Change to a different modality
• Limit or modify the scan range
• Review outside CTs to determine whether a follow
  up CT is indicated

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What GSR does

• ACR accreditation
• All IMI sites
• Medicaire requirement 1/2012
• Implementation of dose reduction strategies
• Requires detailed knowledge of CT technology
• Ongoing efforts at tech education and training

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Conclusions

• Advancements in CT imaging have revolutionized
  the practice of medicine
• Increasing utilization has led to an increase in
  population exposure, of particular concern for
  children.
• Radiologists have role as principal gatekeepers
• ALARA principal
• Educate and counsel regarding risks