1. CT Radiation: What is the Radiation Risk to Your Patient?
Pediatric Conference 5/19/2015
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
LMEF

2. Disclosures
None

5. 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

6. 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

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Marshall island craters bomb test spectators
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8. Pediatric Conference 5/19/2015
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10. Shoe-Fitting Fluoroscope 1930’s-50’s

11. 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.

12. 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.

13. 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

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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
Graph electromagnetic frequencies
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16. Radiation Biology X-ray absorbed DNA strand breaks Recoil electron
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

17. Radiation Biology

18. Radiation Biology Three biological effects of concern
Heritable Effects
Effects on the Developing Embryo and Fetus
Radiation Carcinogenesis

19. Radiation Biology Three biological effects of concern
Heritable Effects
Effects on the Developing Embryo and Fetus
Radiation Carcinogenesis

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Children are Unique
More sensitive to carcinogenic effects
Cells are rapidly dividing
Longer lifespan
Risk is greatest in early life
Diagram for risk for age
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22. Biological Effects Deterministic effects Stochastic effects
Dose threshold
Preventative
Fluoroscopy Skin burns
Stochastic effects
No threshold
Occurrence is dose-dependent
Severity independent of dose
Tumor

23. Biological Effects Deterministic effects Stochastic effects
Dose threshold
Preventative
Fluoroscopy Skin burns
Stochastic effects
No threshold
Occurrence is dose-dependent
Severity independent of dose
Tumor
Hall, Eric J. Radiation Biology for Pediatric Radiologists. Pediatr Radiol (2009) 39 (Suppl 1):S57-S64

24. Deterministic Effects
18-21 months post coronary angiography
Shope, Thomas B. Radiation-induced skin injuries from fluoroscopy. Radiographics 1996; 16:

25. 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

26. Assume No Threshold No threshold model Attributable risk
Dose
(Hormesis)

27. Quantitative Prospective Studies re: Radiation Exposure and Cancer Risk
Number of randomized controlled trials comparing medical radiation exposure to cancer risk:

28. Quantitative Prospective Studies re: Radiation Exposure and Cancer Risk
Number of randomized controlled trials comparing medical radiation exposure to cancer risk:

29. Studied Population Exposure type Effects
Early radiologists
Fluoroscopy, scatter, brachytherapy
Leukemia, cataracts, skin cancers
Japanese atomic bomb survivors
Direct gamma exposure, fallout (I-131)
Leukemia, thyroid cancers, congenital defects
Marshall Island survivors
Fallout (mostly I-131)
Thyroid cancers
Tinea capitis patients
Gamma to head
Thymoma patients
Gamma to neck
"Radium girls"
Radium ingestion
Oropharyngeal cancers, bone sarcomas, leukemia
Uranium miners
Inhaled radon
Lung cancer
Chest fluoroscopy in TB sanitaria (prior to 1953)
Gamma to breast
(doses were VERY high)
Breast cancer

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Early radiologist From the movie “the Fall”
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Scalp necrosis after gamma therapy for tinea capitis
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34. 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

35. 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

36. 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

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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.
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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.
LMEF

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2006
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Slovis T. Where we were, what has changed, what needs doing: a decade of progress. Pediatr Radiol (2011) 41 (suppl 2): S456-S460.
LMEF

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2006
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48%
Slovis T. Where we were, what has changed, what needs doing: a decade of progress. Pediatr Radiol (2011) 41 (suppl 2): S456-S460.
LMEF

41. Why CT? Not most common exam CT scans largest contributor
7 million CT exams in children/year in US
Dose ~100x

42. Effects of CT Radiation
Risk from low-level radiation from single pediatric CT uncertain
Challenge
US risk cancer 25%
Added risk CT %
Inherent uncertainties
Dose calculation
Frush, Donald P. Ct dose and risk estimates in Children. Pediatr Radiol (2011) 41 (Suppl 2): S483-S487

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CT Dose Estimate
Dose
CTDI vol
DLP
Age patient
Sex patient
Exam type
Organ dose: phantoms- computerized simulated body 3D
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44. CT Dose Estimate Objective Data Estimate CTDI volume: CT output
Based on phantom data
DLP: Length irradiated
Estimate
Wrong by an order of magnitude
No organ-specific risk

45. 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.

46. 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:

47. 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

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Results
1 excess case of leukemia and 1 brain tumor per 10,000 children
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49. 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

50. Even if the 1 in 10,000 number is true, how many of those 10,000 lives were saved or prolonged by their scan?

51. 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 x 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…

52. 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 long-term 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.

53. 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

58. Riley Hospital for Children
Low Dose
Prior and ongoing studies working to decrease dose
CT, radiography, fluoroscopy

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Tube mAs Modulation —
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60. Tailored Dose for Every Patient
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Tailored Dose for Every Patient
Water equivalent diameter
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Average dose reduction 20%
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Abdomen CT Scan Dose
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Chest CT Scan Dose
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Head CT Scan Dose
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66. 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

67. 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

68. CT Dose Reporting at Riley
Pediatric Conference 5/19/2015
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:
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69. 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)

70. Communicating Radiation Risk to Patients and Families

71. 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?

72. 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

73. 2. How Much Radiation is my Child Receiving?
Exam
Background Radiation
Chest x-ray
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

74. 3. Will this Cause Cancer in my Child?
We really do not know
Differing medical opinions
Estimated risk of cancer from 1 single CT % over lifetime
Compares to 25% baseline risk

75. 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
Ultrasound, MRI

76. 5. Where can I Learn More? Image Gently
Society of Pediatric Radiology website

77. Image Gently
“…Goal is to change practice by increasing awareness of the opportunities to promote radiation protection in the imaging of children”

78. Image Gently
Referring physicians, radiologists, technologists, physicists
Parents
FAQs

79. Image Gently Informational brochures CT Fluoroscopic procedures
Interventional procedures
Nuclear Medicine
Digital Radiography

80. Image Gently
“My Child’s Medical Imaging Record”

81. 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

82. Helpful Information www.imagegently.org
xkcd.com/radiation/
iuhealth.org/riley/radiology-imaging/

83. Helpful Information Riley Radiology: Pediatric Radiologist
iuhealth.org/riley/radiology-imaging/

84. Riley Hospital for Children

85. Thank You

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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. Published online June 7, Pierce D, Preston D. Radiation-related cancer risks at low doses among atomic bomb survivors. Radiat Res (2000), 154: Brenner D, Elliston C, Hall E, et al. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR (2001) 176: Slovis T. Where we were, what has changed, what needs doing: a decade of progress. Pediatr Radiol (2011) 41 (suppl 2): S456-S 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), Norris B, Wilson J. Childata: The handbook of child measurements and capabilities – data for design safety. London, UK: Dept Trade and Industry, Peebles L, Norris B. Adultdata: The handbook of adult anthropometric and strength measurements – data for design safety. London, UK: Dept Trade and Industry, 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), 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-S Brenner, David J.; Hall, Eric J. (2007). "Computed Tomography — an Increasing Source of Radiation Exposure". New England Journal of Medicine 357 (22):
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87. References
11. Image Gently. 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
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):
Brenner DJ, Elliston CD, Hall EJ et al (2001) Estimated Risks of radiation-induced fatal cancer from pediatric CT, AJR 176:
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.
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):
Shope, Thomas B. Radiation-induced skin injuries from fluoroscopy. Radiographic 1996; 16: