CT Radiation: What is the
Radiation Risk to Your Patient?
May 19, 2015
Megan Marine, MD
Assistant Professor of Radiology and Imaging Sciences
Pediatric Radiology Division
Disclosures
• None
Objectives
• Understand the risks of ionizing radiation
• Discover specifically the effects of CT radiation
and how dose can be decreased
• Learn how to communicate radiation risk to
patients and their families
Objectives
• Understand the risks of ionizing radiation
• Discover specifically the effects of CT radiation
and how dose can be decreased
• Learn how to communicate radiation risk to
patients and their families
Shoe-Fitting Fluoroscope 1930’s-50’s
Risks of Radiation:1949
• “…present evidence indicates that at least
some radiation injuries are statistical
processes that do not have a threshold…there
is no exposure which is absolutely safe and
which produces no effect.”
Lewis, Leon; Caplan, Paul E. “The Shoe-Fitting Fluoroscope as a
Radiation Hazard.” California Medicine 72 (1): 27. Jan 1, 1950.
Risks of Radiation:1949
• “…present evidence indicates that at least
some radiation injuries are statistical
processes that do not have a threshold…there
is no exposure which is absolutely safe and
which produces no effect.”
Lewis, Leon; Caplan, Paul E. “The Shoe-Fitting Fluoroscope as a
Radiation Hazard.” California Medicine 72 (1): 27. Jan 1, 1950.
Background
• Radiation = Energy emitted from any source
• 2 Types:
– Ionizing Radiation: High frequency with energy to
remove electron from atom/molecule
• X-rays, gamma rays, UV rays
– Non-ionizing Radiation: Low energy; do not
directly damage DNA
• Visible light, infrared rays, microwaves, radiowaves
Background
• Radiation = Energy emitted from any source
• 2 Types:
– Ionizing Radiation: High frequency with energy to
remove electron from atom/molecule
• X-rays, gamma rays, UV rays
– Non-ionizing Radiation: Low energy; do not
directly damage DNA
• Visible light, infrared rays, microwaves, radiowaves
Radiation Biology
• X-ray absorbed
– Recoil electron
• DNA strand breaks
– Single strand breaks
– Double strand breaks
• Unrepaired: Incorrect joining two chromosomes
• Basic lesion for biological effects of radiation
Hall, Eric J. Radiation Biology for Pediatric Radiologists. Pediatr
Radiol (2009) 39 (Suppl 1):S57-S64
Radiation Biology
Radiation Biology
• Three biological effects of concern
– Heritable Effects
– Effects on the Developing Embryo and Fetus
– Radiation Carcinogenesis
Radiation Biology
• Three biological effects of concern
– Heritable Effects
– Effects on the Developing Embryo and Fetus
– Radiation Carcinogenesis
Children are Unique
• More sensitive to carcinogenic effects
– Cells are rapidly dividing
• Longer lifespan
• Risk is greatest in early life
Biological Effects
• Deterministic effects
– Dose threshold
– Preventative
– Fluoroscopy Skin burns
• Stochastic effects
– No threshold
– Occurrence is dosedependent
– Severity independent of
dose
– Tumor
Biological Effects
• Deterministic effects
– Dose threshold
– Preventative
– Fluoroscopy Skin burns
• Stochastic effects
– No threshold
– Occurrence is dosedependent
– Severity independent of
dose
– Tumor
Hall, Eric J. Radiation Biology for Pediatric Radiologists. Pediatr
Radiol (2009) 39 (Suppl 1):S57-S64
Deterministic Effects
• 18-21 months post coronary angiography
Shope, Thomas B. Radiation-induced skin injuries from
fluoroscopy. Radiographics 1996; 16:1195-1199.
Risk Models: Threshold
• 1949
– …”statistical processes that do not have a
threshold”…
• No threshold model
• Linear increase in risk for any dose
• Linear threshold assumes a finite minimum dose
below which there is no increased risk
– Hormesis assumes a threshold below which
radiation may have a (small) beneficial effect
Assume No Threshold
Attributable risk
(Hormesis)
Dose
Quantitative Prospective Studies re:
Radiation Exposure and Cancer Risk
• Number of randomized controlled trials comparing
medical radiation exposure to cancer risk:
Quantitative Prospective Studies re:
Radiation Exposure and Cancer Risk
• Number of randomized controlled trials comparing
medical radiation exposure to cancer risk:
0
Studied
Population
Early
radiologists
Japanese
atomic bomb
survivors
Marshall Island
survivors
Tinea capitis
patients
Thymoma
patients
Exposure type
Fluoroscopy, scatter,
brachytherapy
Effects
Leukemia, cataracts, skin
cancers
Direct gamma exposure,
fallout (I-131)
Leukemia, thyroid cancers,
congenital defects
Fallout (mostly I-131)
Thyroid cancers
Gamma to head
Thyroid cancers
Gamma to neck
Thyroid cancers
"Radium girls"
Radium ingestion
Uranium miners
Chest
fluoroscopy in
TB sanitaria
(prior to 1953)
Inhaled radon
Gamma to breast
(doses were VERY high)
Oropharyngeal cancers,
bone sarcomas, leukemia
Lung cancer
Breast cancer
Risk Model Issues
• Based on retrospective data
• Based on doses much, much higher than are used in
diagnostic imaging currently
– i.e. atomic bomb survivors
– Can we assume a linear relationship between a single
acute very high dose and multiple/fractionated low doses
accumulated over long periods of time?
• Assumes a “standard” mid-20s, 70 kg, otherwise healthy
patient
– Ethnicity effects?
• Data is population-based/epidemiologic, which is not
necessarily specifiable to individual patient risk
ALARA
• “As Low As Reasonably Achievable”
• Potential low risk at population level
• Conservative approach
– In reducing dose, and thus reducing the assumed
risk, we should take care not to reduce dose to the
point that the study is non-diagnostic
Objectives
• Understand the risks of ionizing radiation
• Discover specifically the effects of CT
radiation and how dose can be decreased
• Learn how to communicate radiation risk to
patients and their families
Early 1980s
Slovis T. Where we were, what has changed, what needs doing: a decade of
progress. Pediatr Radiol (2011) 41 (suppl 2): S456-S460.
Early 1980s
15%
Slovis T. Where we were, what has changed, what needs doing: a decade of
progress. Pediatr Radiol (2011) 41 (suppl 2): S456-S460.
2006
Slovis T. Where we were, what has changed, what needs doing: a decade
of progress. Pediatr Radiol (2011) 41 (suppl 2): S456-S460.
2006
48%
Slovis T. Where we were, what has changed, what needs doing: a decade
of progress. Pediatr Radiol (2011) 41 (suppl 2): S456-S460.
Why CT?
• Not most common exam
– CT scans largest contributor
– 7 million CT exams in children/year in US
– Dose ~100x
Effects of CT Radiation
• Risk from low-level radiation from single
pediatric CT uncertain
• Challenge
– US risk cancer 25%
– Added risk CT 0.03- 0.05%
• Inherent uncertainties
– Dose calculation
Frush, Donald P. Ct dose and risk estimates in Children. Pediatr
Radiol (2011) 41 (Suppl 2): S483-S487
CT Dose Estimate
Age
patient
DLP
CTDI
vol
Dose
Sex
patient
Exam
type
CT Dose Estimate
• Objective Data
– CTDI volume: CT output
• Based on phantom data
– DLP: Length irradiated
• Estimate
– Wrong by an order of magnitude
– No organ-specific risk
Can We Predict Risk for Individual
Patients?
• CTDI and DLP do not represent individual patient dose
– Not designed to characterize dose or risk to individual patients
– Designed for demonstrating exposures of standard populations
• By some estimates, error in estimating cancer risk based on
individual exposures may be up to 500%
– Some data indicate that risk has far more to do with inherent
variability in patient-specific DNA repair capacity than with
radiation dose
• Fanconi’s anemia, Riddle syndrome, ataxia-telangiectasia, etc.
Literature on CT Radiation
• “In the United States, of approximately
600,000 abdominal and head CT examinations
annually performed in children under the age
of 15 years, a rough estimate is that 500 of
these individuals might ultimately die from
cancer attributable to the CT radiation.”
– Death from cancer will increase from 25% to
25.08%
Brenner DJ, Elliston CD, Hall EJ et al (2001) Estimated Risks of radiation-induced fatal cancer from
pediatric CT, AJR 176:289-296.
That Lancet article
• 179,000 pediatric patients receiving head CT
(283,919 total scans)
Radiation exposure from CT scans in childhood and subsequent risk of
leukaemia and brain tumours: a retrospective cohort study Lancet,
Volume 380, No. 9840, p499–505, 4 August 2012
Results
• 1 excess case of leukemia and 1 brain tumor
per 10,000 children
But… Limitations
• No standardization of scan protocol
• Dates of scans from 1985 to 2002
– Protocols are MUCH improved, doses MUCH lower
• Questionable statistics
• The authors themselves acknowledge:
– Risk found in the study very small compared with
the lifetime cancer risk of the general population
– Risk likely small compared with the benefits of a
clinically justified scan
Even if the 1 in 10,000 number is
true, how many of those 10,000
lives were saved or prolonged by
their scan?
Even if the 1 in 10,000 number is true,
how many of those 10,000 lives were
saved or prolonged by their scan?
• Estimated latency of 2 years for leukemia, 5 years for
thyroid cancer, 10+ years for solid tumors
• Observed risk of a patient dying within 5 years from
underlying disease process is 10-100x higher than the
theoretical risk of a leukemia or thyroid cancer
• The yield of brain injury detection in pediatric head CT
based on established CDM tools (blunt head trauma
setting) is 1-8%
• Yield of an urgent incidental finding is ~1/700
• Compared to 1/10,000 reported cancer risk…
ACR’s Official Response
…results of a study (Pearce et al) to be published in the
Lancet … should not keep parents from getting
needed medical imaging care for their children
If an imaging scan is warranted, the immediate
benefits outweigh what is still a very small longterm risk. Children who get CT scans are doing so
because of an immediate and significant health
condition. These are not screening exams given to
the general population of children.
Recently…
Estimated risk of radiation-induced cancer from paediatric chest
CT: two-year cohort study
• Pediatric Radiology, March 2015 issue
• 2 year cohort of 522 patients
• Relative risk of a chest CT is miniscule compared to lifetime
baseline population risk
– But not 0 – risk/benefit analysis and appropriateness criteria for
studies must still be followed
http://www.ucdmc.ucdavis.edu/radiology/health_info/CT_risk.pdf
http://www.ucdmc.ucdavis.edu/radiology/health_info/CT_risk.pdf
Riley Hospital for Children
• Low Dose
• Prior and ongoing studies working to decrease
dose
– CT, radiography, fluoroscopy
Tube mAs Modulation
Tailored Dose for Every Patient
Water equivalent diameter
Chest CT scan dose reduction
from tube modulation
60%
50%
40%
Dose reduction 30%
20%
10%
0%
0
20
40
60
Body weight (Kg)
Average dose reduction 20%
80
100
Abdomen CT Scan Dose
14
12
10
8
CTDIvol
Riley
6
UK post 2001
4
2
0
0
5
10
Age (years)
15
20
Chest CT Scan Dose
12
Chest CT scans dose
10
12
10
8
8
CTDIvol 6
Riley
CTDIvol 6
UK post 2001
Riley
4
4
UK post 2001
2
0
0 0
0
5
5
10
10
Age (years)
Age (years)
15
15
20
20
Head CT Scan Dose
60
50
40
CTDIvol 30
Riley
UK post 2001
20
10
0
0
5
10
Age (years)
15
20
Conclusions of CT Radiation Risk
• Literature demonstrates low risk
• No direct evidence that diagnostic CT
increases mortality
• Assumption exists : ALARA
– Any radiation carries minimal risk
Objectives
• Understand the risks of ionizing radiation
• Discover specifically the effects of CT radiation
and how dose can be decreased
• Learn how to communicate radiation risk to
patients and their families
CT Dose Reporting at Riley
CT output Dose:
CTDIvol (32 cm phantom): […] mGy
We do our best to maintain the CT radiation dose as
low as possible. The risk from CT radiation is very
low. CTDI represents CT radiation dose output and
not the risk or dose absorbed by the patient. These
measurements help us ensure a maintenance of low
dose CT scans. More information on CT radiation
parameters and risks can be found at:
http://iuhealth.org/riley/radiology-imaging/ct-scan/
California Law: July 2013
• Dose documentation of every CT study
• Annual verification of dose calculations/scanner
calibration by medical physicist
• Required reporting of dose errors to patients (more
than 20% above DRL)
Communicating Radiation Risk to
Patients and Families
5 Common Questions
1. What are the risks from medical radiation?
2. How much radiation is my child receiving?
3. Will this cause cancer in my child?
4. How can we minimize the radiation dose?
5. Where can I learn more?
1. What are the Risks from Medical
Radiation?
• No conclusive evidence radiation from
diagnostic x-rays causes cancer
• Studies large populations exposed to radiation
demonstrate slight increases in cancer risk
• To be safe, act as low doses radiation may
cause harm
2. How Much Radiation is my Child
Receiving?
Exam
Background
Radiation
Chest xray
1 Day
Head CT
Up to 8
months
Abdominal
CT
Up to 20
months
Background Radiation= Soil, rocks, building materials, water, air, and cosmic radiation
3. Will this Cause Cancer in my Child?
• We really do not know
• Differing medical opinions
• Estimated risk of cancer from 1 single CT 0.030.05% over lifetime
– Compares to 25% baseline risk
4. How can we Minimize Radiation
Dose?
• Risks versus benefits
– ACR Appropriateness Criteria
• Avoid multiple scans when possible and image
only indicated area
• Alternative studies
100
90
80
– Ultrasound, MRI
70
60
MR enterography
50
CT enterography
40
30
20
10
0
2010
2011
5. Where can I Learn More?
• Image Gently
• Society of Pediatric Radiology website
• http://www.pedrad.org
Image Gently
• “…Goal is to change practice by increasing
awareness of the opportunities to promote
radiation protection in the imaging of
children”
Image Gently
• Referring physicians, radiologists,
technologists, physicists
• Parents
• FAQs
Image Gently
• Informational brochures
– CT
– Fluoroscopic procedures
– Interventional procedures
– Nuclear Medicine
– Digital Radiography
Image Gently
• “My Child’s Medical Imaging Record”
Conclusions
• The risk of an individual scan is extremely
difficult to quantify precisely, but is certainly
miniscule
• When a CT scan is indicated, the risk of not
getting the scan almost always outweighs the
risk of the scan itself
– ACR Appropriateness Criteria Worksheet
Helpful Information
• www.imagegently.org
• www.informationisbeautiful.net/visualizations
/radiation-dosage-chart/
• xkcd.com/radiation/
• www.imagewisely.org
• iuhealth.org/riley/radiology-imaging/
Helpful Information
•
•
•
•
Riley Radiology: Pediatric Radiologist
iuhealth.org/riley/radiology-imaging/
317-948-6315
mbshelto@iupui.edu
Riley Hospital for Children
Thank You
References
1.
Peace M, Salotti J, Little M, et al. Radiation exposure from CT scans in childhood and subsequent
risk of leukemia and brain tumors: A retrospective cohort study. www.thelancet.com. Published
online June 7, 2012.
2. Pierce D, Preston D. Radiation-related cancer risks at low doses among atomic bomb survivors.
Radiat Res (2000), 154:178-186.
3. Brenner D, Elliston C, Hall E, et al. Estimated risks of radiation-induced fatal cancer from pediatric
CT. AJR (2001) 176:289-296.
4. Slovis T. Where we were, what has changed, what needs doing: a decade of progress. Pediatr Radiol
(2011) 41 (suppl 2): S456-S460.
5. Shrimpton, P, Hillier M, Lewis M, Dunn M. National survey of doses from CT in the UK:2003. The
British Journal of Radiol, 79 (2006), 968-980.
6. Norris B, Wilson J. Childata: The handbook of child measurements and capabilities – data for design
safety. London, UK: Dept Trade and Industry, 1995.
7. Peebles L, Norris B. Adultdata: The handbook of adult anthropometric and strength measurements
– data for design safety. London, UK: Dept Trade and Industry, 1998.
8. Kim K, Gonzalez A, Pearce M, et al. Development of a database of organ doses for pediatric and
young adult CT scans in the UK. Radiation Protection Dosimetry (2012), 1-12.
9. Linet M, Kim K, Rajaraman P. Children’s exposure to diagnostic medical radiation and cancer risk:
epidemiologic and dosimetric considerations. Pediatr Radiol (2009) 39 S4-S26.
10. Brenner, David J.; Hall, Eric J. (2007). "Computed Tomography — an Increasing Source of Radiation
Exposure". New England Journal of Medicine 357 (22): 2277-2284.
References
11. Image Gently. http://www.pedrad.org/associations/5364/ig/. Accessed September 2012.
12. Kleinerman, Ruth A. Radiation-sensitive genetically susceptible pediatric sub-populations.
Pediatr Radiol (2009) 39 (Suppl 1):S27-S31
13. Hall, Eric J. Radiation Biology for Pediatric Radiologists. Pediatr Radiol (2009) 39
(Suppl 1):S57-S64
14. Frush, Donald P. Ct dose and risk estimates in Children. Pediatr Radiol (2011) 41 (Suppl 2):
S483-S487
15. Jablon, Seymour MA; Hrubec, Zdenek, ScD; Boice, John D Jr, ScD . Cancer in Populations Living Near
Nuclear Facilities: A Survey of Mortality Nationwide and Incidence in Two States. JAMA.
1991;265(11):1403-1408.
16. Brenner DJ, Elliston CD, Hall EJ et al (2001) Estimated Risks of radiation-induced fatal cancer from
pediatric CT, AJR 176:289-296.
17. Linet MS, Kim KP, Rajaraman P (2009) Children’s exposure to diagnostic medical radiation and
cancer risk: epidemiologic and dosimetric considerations. Pediatr Radiol 39:S4-S26.
18. Brenner DJ, Doll R, Goodhead DT et al. (2003) Cancer risks attributable to low doses of ionizing
radiation: assessing what we really know. Proc Nat Acad Sci USA 100(24):13761-13766.
19. Shope, Thomas B. Radiation-induced skin injuries from fluoroscopy. Radiographic 1996; 16:11951199.