Transcript Understanding Radiation Risk from Diagnostic Imaging Wednesday, July 23, 2008 12:00 – 1:00 p.m.

Understanding Radiation Risk from
Diagnostic Imaging
Wednesday, July 23, 2008
12:00 – 1:00 p.m. EDT
© American Academy of Pediatrics 2008
Moderator:
Marlene R. Miller, MD, MSc, FAAP
Vice President, Quality - NACHRI
Director of Quality and Safety & Associate Professor
Johns Hopkins Children’s Centers
Baltimore, Maryland
DISCLOSURES
Financial Relationships
One individual involved in this webinar:
Melissa A. Singleton, M.Ed., Project Manager-Consultant
has disclosed a financial relationship with an entity producing,
marketing, re-selling, or distributing health care goods or
services consumed by, or used on, patients. Her husband is
employed by Walgreen Co. as a Workforce Administration
Manager (technology position) for the company’s call centers.
The AAP determined that this financial relationship does not
relate to the educational assignment.
None of the other involved individuals (Speakers, Moderators,
Project Advisory Committee members, or Staff) has disclosed a
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Speaker:
Alan S. Brody, MD, FAAP
Professor of Clinical Radiology and Pediatrics
Division Chief of Thoracic Imaging
Associate Director of Radiology Research, IRC
Cincinnati Children’s Hospital Medical Center
Cincinnati, Ohio
LEARNING OBJECTIVES
Upon completion of the webinar, participants will be able to:



Discuss the radiation risk from CT scanning with patients
and families.
Compare the amount of radiation from different ionizing
radiation exposures.
List methods that should be used to limit radiation
exposure from CT scanning.
Understanding
Radiation Risk From
Diagnostic Imaging
Alan S. Brody, MD
Professor of Radiology and Pediatrics
Chief, Thoracic Imaging
Cincinnati Children’s Hospital
Disclosures
I
have no financial disclosures
Disclosures
I
have no financial disclosures
but
Disclosures
I
have no financial disclosures
but
I
use CT scanning in my clinical
practice
 My research interests include CT
scanning in cystic fibrosis and
interstitial lung disease
Overview
 Radiation
risk from diagnostic
imaging
 Benefits of diagnostic imaging
 Maximizing the benefit/risk ratio
 Discussing risk with patients and
families
Why the Recent
Concern?
Increasing CT Scans
 CT
scanning is almost universally
available
 The number of CT scans is increasing
every year
 Indications for CT use are increasing,
and may not consider possible risks
New Risk Information
 Low
dose radiation risk estimates
from atomic bomb data are now
available for radiation dose levels
similar to the radiation dose from
one CT scan
One Paper Started it All
 Estimating
Risks of RadiationInduced Fatal Cancer from
Pediatric CT
– David J. Brenner
– Carl D. Elliston
– Eric J. Hall
– Walter E. Berdon
AJR 2001:176:289-296
CT Scans in Children Linked To
Cancer Later
 “Each
year about 1.6 million children
in the USA get CT scans to the head
and abdomen -- and about 1,500 of
those will die later in life from
radiation-induced cancer”
 Steve Sternberg, front page, USA
Today, January 22, 2001
American Journal of
Roentgenology February, 2001
 One
CT scan carries a 1 in 1000
risk of a fatal cancer
– Brenner, et al.
 CT
dose for children is often higher
than necessary
– Patterson, et al.
 Simple
methods can decrease CT
dose for children
– Donnelly, et. al
Radiation Risk
from
Diagnostic Imaging
Ionizing Radiation
Radiation capable of producing ionization
in tissues and which can be absorbed
 Continuously present in our environment

– background radiation

Average exposure 3 mSv/year in US,
varies widely
– Cosmic rays, radon, radiation from rock,
natural radionuclides
– 4-5 mSv in Denver
Ionizing Radiation
 Used
in diagnostic imaging
– Radiography, fluoroscopy, angiography,
nuclear medicine, CT scanning
 Medical
radiation is the largest
source of man-made radiation
Radiation from
Diagnostic Imaging
CT Scanning Use
From 1991 to 1999 CT scans increased
from 6.1% to 11% of radiology
procedures in a busy academic center
 CT scanning accounted for 67% of the
effective dose from diagnostic radiology
 11% of the patients were less than 16

Mettler, J. Radiol. Prot. 20 (2000) 353-359
CT Scanning
 2000
– 11% of exams, 67% of dose
– Mettler, J. Radiol. Prot. 20 (2000) 353-359
 2002
– 15% of exams, 75% of dose
– Weist Semin Ultrasound CT MR. 2002;23:402-10
Why Emphasize CT?
 CT
provides 75% of the current US
population radiation exposure from
diagnostic imaging
 CT
use continues to grow
 Methods
are available to markedly
reduce dose
Radiation from Diagnostic Imaging
 Upper
GI series and VCUG have
radiation doses similar to CT
scanning
One CT can has the same
radiation dose as about how
many chest radiographs?
1.
2.
3.
4.
0.5
10
50
100
Estimated Medical Radiation Doses
for 5 Year-Old Child
Effective Dose
(mSV)
Equivalent
Number of CXRS
3-view ankle
.0015
1/14th
2-view chest
.02
1
Anteroposterior and lateral abdomen
.05
2.5
Tc-99m2 radionuclide cystogram
.18
9
Tc-99m radionuclide bone scan
6.2
310
FDG PET3 scan
15.3
765
Upper GI/small bowel follow through
1
50
Head CT
4
200
Chest CT
3
150
Abdomen CT
5
250
Imaging Area
CXR, chest radiograph; Tc99m, technetium 99m; FDG PET, fluorodeoxygluecose positron emission tomography.
Data provided by R. Reiman MD. Personal Communication. Duke Office of Radiation Safety.
http://www.safety.duke.edu/RadSafety/
Things We Know About Ionizing
Radiation
 High
dose radiation (> 100 mSv) is
known to increase the risk of cancer
 Children
adults
are at higher risk than
Radiation Risk for Children
 Cancer
risk increases with decreasing
age
 The smaller the patient the higher
the exposure from the same
technique
Risk is Age Dependent
Cancer risk for
a 4 year old is
likely 3-5 times
greater than for
a 40 year old
_____ ICRP 60
_ _ _ _ BEIR V
Dose is Size Dependent
Dose in a
4 year old
is up to
two times
higher than
in a 40
year old
Things We Don’t Know About
Radiation
 How
low level radiation (below 100
mSv, especially below 10 mSv)
affects the risk of cancer
Risk from Low Dose Radiation
 The
body of literature on low level
radiation is large and confusing
 Data are available to support
increased, decreased, or no risk of
cancer
 Few of these data are taken from
diagnostic imaging exposure
 All of the data are open to
interpretation
Consensus Statements
on Radiation Risk
Biological Effects of Ionizing Radiation
Report VII
US National Academy of Science
“A comprehensive review of the available
biological and biophysical data supports
a “linear no threshold” (LNT) risk
model-that the risk of cancer proceeds
in a linear fashion at lower doses
without a threshold and that the
smallest dose has the potential to cause
a small increase in risk to humans”
Health Physics Society
“There is substantial and convincing
scientific evidence for health risks
following high-dose exposures.
However, below 50-100 mSv, risks of
health effects are either too small to
be observed or are nonexistent”
Health Physics Society
“The Society has concluded that
estimates of risk should be limited to
individuals receiving a dose of 50
mSv in one year or a lifetime dose of
100 mSv in addition to natural
background.”
The Definitive Study
 The
background fatal cancer rate is
approximately 20%
 Assume a 1 in 2000 risk of a fatal
cancer from diagnostic imaging
 The study must detect the difference
between 0.2000 and 0.2005
 Millions of subjects would be needed
Land, Science 1980;209:1197-1203
The Definitive Study
 Other
methodologies, such as case
control studies, require fewer
subjects
 These studies are open to additional
methodological criticism
 A convincing answer is unlikely soon
 It is impossible to prove a negative
Land, Science 1980;209:1197-1203
I Need a Number
 The
most widely used estimate of
risk of cancer from ionizing radiation
is 5% per sievert (Sv).
 Diagnostic imaging doses are in the
millisievert (mSv) range (5 mSv for
abdominal CT)
 Risk for 1 CT = 1 in 4,000
What Should We Do?
Is it reasonable to believe that
ionizing radiation from diagnostic
imaging can increase cancer?
Is it reasonable to believe that
ionizing radiation from diagnostic
imaging can increase cancer?
What is the benefit that
justifies this risk?
Benefit of CT Scanning
CT Alters Treatment
 Children
with seizures
 Adults with stroke
 Blunt abdominal trauma
 Appendicitis
 Spine trauma
 Diffuse lung disease
Avoiding Surgery
 29,200
children undergoing general
anesthesia
 95% normal or mild systemic disease
Cohen MM, Anesth Analg 1990;70:160-167
Risk of Surgery
 29,200
children undergoing general
anesthesia
 95% normal or mild systemic disease
 1 in 30 risk of a “major event”
Cohen MM, Anesth Analg 1990;70:160-167
Risk of Surgery
 29,200
children undergoing general
anesthesia
 95% normal or mild systemic disease
 1 in 30 risk of a “major event”
 1 in 2500 risk of death
Cohen MM, Anesth Analg 1990;70:160-167
Risk of Hospitalization
 33,000,000
hospital admissions
annually in the United States
 44,000 to 98,000 deaths from
medical errors
 > 1 in 1000 risk of death from a
medical error per hospitalization
Kohn, National Academy Press 2000
http://newton.nap.edu/books/0309068371/html/
index.html
If an institution performs 300 CT
scans per year, the risk benefit
equation balances if CT saves one
life every 4 years
“a no brainer”
Haaga AJR 2001;177:289-291
Maximizing the
Benefit/Risk Ratio
Maximizing the Benefit/Risk Ratio
 Consider
modalities that do not use
ionizing radiation
 Optimize imaging protocols
 Decrease unnecessary examinations
 ALARA
 Image quality
Is Radiation Necessary?
 Magnetic
resonance imaging
 Ultrasound
 Non-imaging evaluation
Is Radiation Necessary?
 Magnetic
resonance imaging
 Ultrasound
 Non-imaging evaluation
 Not
doing a CT scan reduces the
radiation by 100%
Maximizing the Benefit/Risk Ratio
 ALARA
(As low as reasonably
achievable) CT technique
 Designing imaging protocols to
reduce radiation exposure
 Reducing unnecessary imaging
CT Scanning and Dose
 Changing
CT dose primarily affects
images by altering image noise
 Higher dose results in decreased
image noise
 The larger the patient, the higher the
dose needed to produce the same
amount of noise
CT #1
CT #2
Which CT Is Noisier?
#1
#2
#1 Had Twice the Dose of #2
#1
#2
CT #5
CT #6
Which CT Is Noisier?
#5
#6
#5 Had Three Times the Dose of #6
#5
#6
#5 Had Three Times the Dose of #6
21 years old
4 years old
Weight
(kg)
mAs
kVp
Slice
Interval
(mm)
1-7.5
10-20
100
5
7.5-10
20-25
100
7.5
10-12.5
30
100
7.5
12.5-15
25
120
10
15-20
30
120
10
20-25
35
120
10
25-35
40
120
10
35-50
45
120
10
50-70
50
120
10
Adult
100
120
10
Technique for
High–Resolution
Chest CT
Imaging Protocols
Imaging Protocols that Reduce
Radiation Exposure
 Scan
only the area of interest
 Use techniques that require less
radiation
6 Year Old, Pulmonary Cavity
?
Underlying congenital abnormality
 CT
scan showed no other disease
 Chest radiograph showed improvement
 CT scan requested to re-evaluate
6 Year Old, Pulmonary Cavity
?
Underlying congenital abnormality
 CT
scan showed no other disease
 Chest radiograph showed improvement
 CT scan requested to re-evaluate
 Limit
CT to upper lobes, avoid thyroid
 Use breast shields
Pulmonary Embolism Imaging at
a Children’s Hospital
Increasing requests for CT pulmonary
angiograms in children prompted a review
of imaging
 Most pediatric chest radiographs are
normal or minimally abnormal, decreasing
the number of indeterminate ventilation
perfusion scans
 Additional diagnoses such as heart disease
and cancer rare in children

Pulmonary Embolism Imaging
 15%
of ventilation perfusion scans
indeterminate
 10% of CT pulmonary angiograms
technically limited
 Breast dose with CT 30X greater
than with ventilation/perfusion scan
Pulmonary Embolism Imaging
 15%
of ventilation perfusion scans
indeterminate
 10% of CT pulmonary angiograms
technically limited
 Breast dose with CT 30X greater
than with ventilation/perfusion scan
 Perfusion
scanning recommended as
first study in patients with normal
CXRs
Limiting Examinations
Limiting Examinations
 1/3
of diagnostic examinations in the
United States are estimated to be
inappropriate or noncontributory
National Imaging Associates web site
6 Year Old, Pulmonary Cavity
6 Year Old, Pulmonary Cavity
 CT
scan ordered “just to check”
 Child doing clinically well
 No surgery planned
CT Scan Cancelled
Pulmonary Embolism
 Deep
vein thrombosis on ultrasound
– Positive in 11 of 15 patients with
pulmonary embolism
 D-dimer
level
– Normal in 0 of 10 patients with
pulmonary embolism
– Elevated in 9 of 12 patients without
pulmonary embolism
Victoria, et al. Society for Pediatric Radiology
Annual Meeting, Miami, FL USA; 21 April 07
CT for Pulmonary Embolism
 IF
D-dimer is negative or if
ultrasound is positive, no chest
imaging other than chest radiograph
is needed
Guidelines
 Many
guidelines are available that
include recommendations for
imaging
 The National Guideline Clearinghouse
– Worldwide guidelines included
– Over 2000 guidelines
– www.guideline.gov
Gastroesophageal Reflux
Upper GI radiation dose approximately
1.5 mSv
 Recommendations of the North American
Society for Pediatric Gastroenterology and
Nutrition
 “A thorough history and physical
examination is generally sufficient to
allow the clinician to establish the
diagnosis of uncomplicated GER (the
‘happy spitter’).”
 “An upper gastrointestinal series is not
required unless there are signs of
gastrointestinal obstruction.”

Image Quality
Chest CT Request
5
yo with chronic cough and failure
to thrive
 On treatment for gastroesophageal
reflux
 Fundoplication planned if CT shows
bronchiectasis
5 Year Old, ? Bronchiectasis
Speaking to Patients
and Families
Speaking to Families and
Patients
 Participation
in medical care should
include the decision to perform
diagnostic imaging
 15% informed of radiation risk of CT
 9% informed of alternatives to CT
scanning
Lee CI AJR 2006;187:282-7
Explaining Radiation Risk
 Families
are more interested in
efforts to control the risk than the
actual number
 After reading a handout on radiation
risk, preference for CT over no
imaging decreased, but no families
refused CT
Larson, et al. AJR 2007:189;271-275
What Do Families Want to
Know?
 The
examination is needed to best
care for their child
 The risk of the examination is real,
but very low
 The examination is being performed
with the lowest possible risk
Summary
 Ionizing
radiation from diagnostic
imaging may cause a very small
increase in the risk of cancer
 For an indicated CT scan, the likely
benefit is far greater than the
estimated risk
 Pediatricians and radiologists should
work together to make the
population exposure ALARA