PETCT, Cardiac CT, Colonography CT : A New IAEA Safety Report Series

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PET/CT, Cardiac CT, Colonography CT A New IAEA
Safety Report Series

• Dawn Banghart, CHP Sr. Health Physicist/Alternate
  Radiation Safety Officer Stanford University

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Introduction

• The IAEA Safety Report Series recently published
  No. 58, 60 and 61 to address safety issues in
• PET/CT (58)
• Cardiac CT (60)
• Virtual Colonography (61)
• This talk will encapsulate key principals and
  standards highlighted in these reports and raise
  the question
• Is it possible to write a comprehensive document
  in this changing technological environment?

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Learning objectives

• After this talk you will be able to
• Site the average effective dose for CT
  Colonography, Cardiac CT and whole body PET/CT
• Ask three very good PET/CT dose optimization
  questions to raise awareness in the clinical
  setting
• List dose reduction strategies for PET/CT staff
• Compare CT Colonography to conventional endoscopy

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IAEA Safety Reports Series

• Four international organizations collaborated to
  produce reports 58, 60 61
• The International Atomic Energy Authority
• The World Health Organization
• The International Society of Radiology
• The International Commission on Radiological
  Protection
• The reports provide guidance and advice for those
  involved in some of the more dose-intensive areas
  emerging in radiology and cardiology today

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Report General Comments

• Pet/CT (No. 58) directed towards patient AND
  staff radiation protection
• Cardiac CT (No. 60) and Virtual Colonography (No.
  61) directed towards patient radiation protection
  ONLY
• All three identify
• Rapid industry growth
• Sharp increase in patient effective dose since
  the emergence of CT technology (1970s) and PET
  technology (2001)
• Expanded applications (e.g., in psychiatry,
  infection imaging)

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Rapid industry growth?Improvements in Technology
CT use has increased from 3 million scans in 1980
to 62 million a year currently (including 4
million kids)
Circa 1975
Present-day, shows six-fold increase in detail
(images courtesy Siemens Medical Systems and
Imaginis.com)
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Beyond new Technology whats up with
dose?Increasing Obesity 1960 - 2000
From CDC's Diabetes Systems Modeling Project
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Whats up with increased applications?
Over the 20th century, the older population grew
from 3 million to 35 million
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Increased CT Scans in Children

• CT scans in children significantly increased
  between 2004 and 2006 and comprised approximately
  810 of the total number of CT scans in the
  USA(1)
• According to a Duke study from 2000 to 2006,
  pediatric ED patient volume increased by 2,
  triage acuity remained stable (2)
• From the same study, pediatric ED number of scans
  increased
• Chest by 435
• Cervical spine CT by 366 (2)
• Children are at greater risk from a given dose of
  radiation compared with adults due to increased
  radiosensitivity of their bodies and a greater
  period of time in which to manifest these
  changes(1).

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What All 3 Reports Share

• Primary concern
• Cancer induction from PET/CT and CT imaging
• Patient benefits from PET/CT and CT imaging will
  have to be balanced against the cost of the
  radiation burden to the individual patient, and
  possibly to the community
• General Aspects of Patient Radiation Protection
  are directed by identifying the practice,
  justifying and optimizing the practice. The must
  dos
• Use of radiation in medicine must do more good
  than harm (i.e., The procedure should improve
  diagnosis)
• Reasonable measures must be employed to improve
  protection and decrease exposure
• Individual cancer risk seems low compared to
  spontaneous incidence, however, there is room for
  improvement with respect to radiation dose
  exposures to the patient

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IAEA Safety Report Series No. 58 Radiation
Protection in Newer Medical Imaging Technologies
PET/CT - Extracted Gems

• Cautions against using effective dose (whole body
  dose) to estimate cancer detriment
• The effective dose intent was to estimate
  detriment to a population (specifically workers
  exposed to radiation)
• Effective dose intended for whole body exposure,
  not partial exposure (e.g., cardiac scan, head
  scan)
• Note Both effective dose and organ dose are
  estimated using phantoms or via Monte Carlo
  calculations
• Pediatric patient effective dose may be
  underestimated
• Patient-specific dose information can not be
  obtained due to height, weight and age
  considerations

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Safety Report Series No. 58 Extracted Gems
continued

• Dose assessment in CT is challenging !!
• On a practical level for patient dose management
  Report Series No. 58 provides three very good
  questions to help raise awareness of dose in the
  clinical setting
• Is a high quality CT scan for PET/CT needed for
  diagnosis or therapy management?
• Can previously acquired anatomical data be used
  for correlative interpretation of PET?
• Can the low dose CT scan be replaced by the
  contrast enhanced diagnostic CT scan?
• Quoting from the reports page 20, image quality
  in CT often exceeds the clinical requirements

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Case in Point - Cedars-Sinai

• Cedars-Sinai error attributed to a
  "misunderstanding" about an incorrectly
  programmed CT machine, remained unchecked for 18
  months, involved 206 people
• Exacerbated nationwide concerns that patients are
  exposed to excess radiation during medical
  testing
• It appears as though Cedars-Sinai group lowered
  the noise ratio which automatically increased mA
  setting
• The chief executive said manufacturers could help
  prevent future errors by
• Improving internal settings and by
• Installing more safeguards

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Typical effective dosesWhole body w/10 mCi FDG
Figure 5. Safety Report Series No. 58
Note Effective dose refers to the detriment to
the whole body
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Staff PET Radiation Protection

• Nuclear medicine technicians receive about 0.3
  0.4 mSv whole body per month performing the usual
  nuclear medicine protocols minus PET (Note
  Radiology Technicians receive minimal
  exposures)
• Technicians dedicated to PET patients will see as
  high as 3 times the above average
• Main Sources of Radiation
• Patient handling
• Unshielded radiopharmaceuticals
• The patient toilet (you know its true!)
• Tasks with greater radiation exposure
• Drawing the dose
• Patient positioning on the scanner bed

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Staff Dose Reduction Strategies

• Exposures to PET radiopharmaceuticals can be
  minimized through
• Good facility design
• Good practice (e.g., conduct patient interviews
  before injection, use shield carrier to transfer
  dose)
• Use unit dose syringes (bulk doses lead to higher
  hand exposures)
• Provide patient instructions/ensure patient
  cooperation (e.g., remind to bring warm clothing,
  any prescribed pain medication, to leave PET
  center when done)
• Minimize time and increase distance by using
  remote video cameras and audio communication

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Question 1

• Of the below dose reduction strategies which task
  might most reduce a nuclear medicine technicians
  exposure?
• a. Using a shield carrier to transfer dose
• b. Conduct patient interviews before lunch
• c. Patient positioning on the scanner bed
• d. Shielded radiopharmaceuticals

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Question 1

• The Correct Answer is
• c. Patient positioning on the scanner bed

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IAEA Safety Series Report Series No. 60 -
Radiation Protection in Newer Medical Imaging
Techniques Cardiac CT

• For several reasons it seems likely that
  pressures will develop to apply new Cardiac CT
  technologies
• Coronary disease is major of cause death in many
  countries
• Accumulation of calcium in coronary arteries may
  predict a future heart attack or other heart
  disease
• Technologies (cardiac CT) are now available to
  monitor the calcification of the coronary
  arteries
• Aging populations for western countries is
  increasing

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The Score on Cardiac CT

• Some authors suggest the use of CT calcium
  scoring in healthy 40-50 year old subjects
• Calcium scoring may be helpful in behavior
  modification programs (i.e., routine follow-up CT
  scans)
• Applications of CT coronary angiography
• Can obviate need for invasive catheterization
  (and its risks)
• Evaluation of artery abnormalities
• Bypass graft condition
• Surgical planning

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Effective Doses (mSv)
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Effective dose (mSv) compared to other common
procedures
Table 2.
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Risk to the patient from Cardiac CT scanning

• Induction of cancer
• Note epidemiological studies have not
  demonstrated excess risk of cancer induction at
  doses less than 100 mSv
• However as the number of procedures per
  individual increases the closer that individual
  gets to the 100 mSv dose
• Authors (3) consider the cumulative effective
  dose of 50 cardiology patients. On average, each
  patient underwent a median of 36 examinations
  Three types of procedures were responsible for
  86 of the total collective effective dose
• Arteriography and interventional cardiology (12
  of examinations, 48 of average dose per
  patient)
• Nuclear medicine (5 of examinations, 21 of
  average dose per patient
• CT (4 of examinations, 17 of average dose per
  patient).
• Median cumulative effective dose was 60.6 mSv

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Cardiac CTPatient Safety Considerations

• Based on cumulative exposures and higher dose
  techniques professional societies view the level
  of detriment set against benefits is too tenuous
  to warrant use of cardiac CT in mass screening
  programs
• Less frequent referrals with identified risk
  profiles (combined with dose reduction
  methodology) provides a more favorable
  risk-benefit profile

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Safety Series Report 61 Radiation Protection in
Newer Medical Imaging Techniques CT
Colonography (CTC)

• The report proposes that CTC might be applied for
  the screening of symptom free patients (but is
  this justified - does CTC benefit outweigh
  harm?)
• Colorectal cancer is the second leading cause of
  deaths from cancer (Europe and USA)
• Screening programs may decrease fatality by
  15-30
• 80 of colorectal cancers arise in persons with
  no known risk factors
• Most carcinomas arise from polyps but the vast
  majority of polyps do not become carcinomas
• There is a direct relationship polyp size and its
  propensity to become malignant

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CTC discussion

• Conventional endoscopy regarded as the gold
  standard against which all other procedures are
  compared
• There are substantial variations in the
  scientific literature in estimates of CTC
  accuracy
• 10 of polyps greater than 1 cm become malignant
  in ten years
• Polyp size has a great influence on detection
  sensitivity

From Table 1.
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Procedure Risks

• Large intestine wall perforation may occur during
  CTC, barium enema, fiberoptic colonoscopy
• The risks for CTC perforation (lt1/2000) are
  higher than the rate quoted for barium enemas and
  lower than that for conventional colonoscocpy
• 40 of patients have CTC abnormalities which may
  be of no clinical interest
• CTC positive findings
• Polyps found should be removed

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Radiation Dose
Table 3.
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CTC Conclusions

• Cancer risk low compared to spontaneous incidence
• As CTC screening increases the number of extra
  cancers from the procedure may also increase
• Proposed CTC screening interval is five years
• Implementation of low dose techniques are likely
• A number of authors have developed innovative
  colonic phantoms to optimize CTC protocols
• Ultra-low dose protocols result in an effective
  dose of 1-2 mSv (even 0.05 mSv shown to be
  feasible!) with polyp detection sensitivity of
  over 80 for polyps greater than 5mm
• Low dose options optimize the procedure, reduces
  risk and perhaps justifies routine use of CTC

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• In conclusion

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The dilemma

• The dilemma expressed to some degree in all three
  reports.
• When sophisticated but expensive equipment is
  available there are inevitable pressures to
  expand applications
• New technologies associated with computed
  tomography are changing rapidly with time,
  providing improved images and, possibly, better
  diagnoses of disease BUT due to radiation dose,
  different considerations need to apply to
  symptomatic and to asymptomatic patients.

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In conclusion

• IAEA Safety Report Series No. 58 , No. 60, No. 61
  are a nice compact introduction to the primary
  and basic challenges with patient and
  occupational radiation exposure from PET/CT and
  CT procedures.
• They are reports to keep in your pocket but
  technologic advances leave a few questions
  unanswered.
• Being one step behind may be the perpetual
  dilemma of all comprehensive reports
• We are still in the wild west

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• Thank you

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• References
• 1) Brenner D. J., Hall E. J. Computed
  tomographyan increasing source of radiation
  exposure. N. Engl. J. Med (2007) 35722772284.
• 2) Broder J., Fordham L. A., Warshauer D. M.
  Increasing utilization of computed tomography in
  the pediatric emergency department, 20002006.
  Emerg. Radiol (2007) 14227232
• 3) Bedetti et al., Cumulative patient effective
  dose in Cardiology, Br Inst Radiology 81
  (2008),699-705