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Increased use of Advanced Medical
Imaging, Radiation Exposure, and
Cancer Risk
Diana L. Miglioretti, PhD
Group Health Research Institute
Rebecca Smith-Bindman, MD
University of California, San Francisco
May 31, 2011 | D. Miglioretti, PhD
Outline
 Background
• Utilization of medical imaging
• Cancer risk from radiation
• Radiation from medical imaging
 Study of dose from CT at 4 San Francisco Bay Area Facilities
• Dose from CT is high and variable
 Study of imaging at 7 integrated healthcare systems
• Imaging utilization and radiation exposure
• CT use in children
• Radiation exposure from CT in children
• Leukemia risk
 Discussion & Conclusions
Benefits of Medical Imaging
 Earlier and more accurate diagnosis of disease
• Earlier treatment
• Improved patient outcomes
 Quick diagnosis (e.g., CT use in ED)
 Less invasive diagnosis
 Accurate prognosis
 Reassurance
Harms Associated with Imaging
 Radiation exposure
 Doses of common exams (e.g., CT) in carcinogenic range
 Rare - accidental overdose
 False positives – Unnecessary follow-up testing, anxiety, cost
 Incidental findings – Cascade of testing to rule out disease
 Overdiagnosis – Unnecessary treatment
 Contrast reactions – Most minor, some major
 Healthcare costs
 Advanced imaging is expensive
2008
CT and MRI
use tripled
in 10 years
Radiation
and Cancer Risk
Measures of Radiation Exposure
 Effective dose (ED)
• Estimates a patient’s overall exposure from non-uniform radiation like
medical imaging
• Accounts for
• amount of radiation from machine
• body part irradiated (sensitivity of organs to radiation)
• patient’s age and possibly gender
• Reflects sensitivity to developing cancer from radiation exposure
• Younger children more sensitive to radiation
• Some organs more sensitive to radiation
• Expressed in milliSieverts (mSv)
BEIR VII Report
 The U.S. National Academies of Sciences Biological Effects of Ionizing
Radiation Committee (BEIR) conducted a comprehensive review of
literature on health risks of low dose radiation exposure
 Members included leading scientists from a broad range of disciplines
 Estimated cancer risk based on dose and age at exposure using a
variety of studies
Japanese Atomic Bomb Survivors
 Life Span Study of the 120,000 survivors of the atomic bombings in
Hiroshima and Nagasaki Japan
 The median dose of survivors was 40 mSv
 Organ specific radiation doses are linked with organ specific cancers
for nearly every cancer
 Even at low doses (10 mSv), survivors were at a significantly increased
risk of developing cancer
Medically Irradiated Populations
Malignant Disease
 Following radiotherapy for malignant disease, there is an elevated risk
of second cancers
 Second primary malignancies particularly high among survivors of
childhood cancer
 Among Hodgkin’s survivors, radiation-induced second primary cancers
are a leading cause of mortality
Medically Irradiated Populations
Benign Disease
 Radiation commonly used 1930-1960 for benign conditions
• Tinea capitis
• Enlarged tonsils
• Enlarged thymus
• Breast conditions (i.e., post partum mastitis)
 Increased risks of radiosensitive cancers
• thyroid, salivary gland, central nervous system, skin, and breast
Medically Irradiated Populations
Repeated X-rays
 Studies have assessed groups who received repeated radiographs
• Scoliosis
• Tuberculosis
• Children with cardiac catheterizations
 All significantly more likely to develop cancer
Radiation Workers
 400,000 radiation workers in the nuclear industry
 Average doses of 20 mSv
 Significant association between exposure (5 - 150 mSv) and cancer
mortality
 Ongoing studies of radiology technologists, physicians who use
radiation suggest increase cancer risks
Summary of Evidence of Harmful Effects of
Radiation
 A large body of epidemiological and biologic evidence links exposure
to radiation (even low doses) with development of cancer
 The results are highly consistent across studies
 “It has not been scientifically demonstrated that any cancer risk exists
below 100 mSv” is untrue
 The A-bomb survivor data provides best dose response data
• However, the effect size is consistent across studies
Radiation Exposure
from Medical Imaging
Imaging Studies Associated with Radiation
Nuclear Medicine (25% of cumulative dose)
• Radioactive material is inhaled, injected, or swallowed
• Gamma rays are emitted by the nuclei, and detected energy is collected
and displayed on a computer
X-Rays (75% of cumulative dose)
• X-rays are generated by a machine, pass through patient to form
pictures on film / computer screen
• Radiographs, fluroscopy, angiography, interventional procedures = 10%
of dose
• CT = 65% of dose
Medical Radiation
 The risks associated with ionizing radiation are not new
• Many of the radiology pioneers developed burns or died from
radiation-induced cancers
 What is new is the dramatic increase in exposures to ionizing radiation
from CT
Radiation Exposure of US Public Has
Doubled Due to Medical Imaging
1985: total 3.7 mSv
75% from natural sources
25% imaging
2006: total 6.2 mSv
50% from natural sources
50% imaging
Sample Annual Radiation Exposures
Source
mSv
Radon
2.0
Living in Denver
0.63
Food
0.40
Sun exposure
0.27
Dental radiographs (series)
0.05
Jet travel (6 hours)
0.03
Airport screening
0.00001
Chest radiographs (PA & Lat)
0.06
CT chest
8.0
CT head, chest, abdomen, pelvis
35-100
Radiation Doses of Common Imaging
Tests
Source
mSv
Chest radiographs (PA & Lat)
0.06
Mammogram series, film-screen
0.80
IVP
2.5
GU contrast studies
1–4
Nuclear medicine renal
2–3
CT head
2.0
CT chest
8.0
CT abdomen & pelvis
12.0
Coronary angiogram
4.6 – 15.8
Nuclear medicine heart
8.9 – 17.0
Radiation Doses from CT: High, Variable,
and Potentially Harmful
 Study of four facilities in San Fran Bay Area
• Smith-Bindman et al., Arch Intern Med, 2009
• Adults, median age 59 years
• January 1 – May 30, 2008
 Dose from CT 1.5-5 times higher than widely cited
• Higher than needed for medical diagnosis
 Doses highly variable for same test and indication
• Vary 15-20 times among facilities
• Even greater variation among patients (even at same facility)
• Expect ~2-fold variation due to differences in body size
Effective Dose for Common CT Types:
Variation within Imaged Region
Typically
Reported
Doses
(mSv)
Mean
Effective
Dose
(mSv)
Equivalent No.
of Chest
Radiographs
Equivalent
No. of
Mammograms
Routine head
2
30
5
Suspected stroke
14
199
33
Routine chest
8
118
20
Suspected pulmonary
embolism
10
137
23
Coronary angiogram
22
309
51
Routine
15
234
39
Multiphase
31
442
74
2–3
Head
Chest
7
Abdomen-pelvis
8 – 10
Smith-Bindman et al., Arch Intern Med, 2009
Effective Dose for Common CT Types:
Variation across Facilities and Patients
Site 1
Site 2
Site 3
Site 4
Range
Across
Patients
Head
Routine head
3
2
3
2
0.3 – 6
Suspected stroke
18
15
8
29
4 – 56
Routine chest
6
12
11
7
2 – 24
Suspected PE
8
21
9
9
2 – 30
Coronary angiogram
21
20
Routine
12
19
20
12
4 – 45
Multiphase
24
35
45
34
6 – 90
Chest
7 – 39
Abdomen-pelvis
Smith-Bindman et al., Arch Intern Med, 2009
Radiation exposure varies among and within CT types
Smith-Bindman et al., Arch Intern Med, 2009
Radiation exposure varies among and within CT types
Smith-Bindman et al., Arch Intern Med, 2009
Average exposure among
Japanese atomic bomb survivors
Why are doses so high and variable?
 No clear dose targets for CT in US
 No professional or governmental organization responsible for
collecting and reporting dose data
 Few clear standards
 Lack of knowledge about dose levels among physicians and
technologists
• May be changing
 Technical improvements in CT have ironically led to increasingly high
doses for more exams
Cancer Risks are Not Trivial
Smith-Bindman et al., Arch Intern Med, 2009
Cancer Risks are Not Trivial
Smith-Bindman et al., Arch Intern Med, 2009
If 1000 20 year old women undergo a
multi-phase abdomen and pelvis CT, 4
are estimated to develop cancer from
the test (range in estimate 2- 12)
Image Utilization
Study of Imaging Use
 Retrospective observational study
 7 integrated healthcare systems
 1994-2007 [adding data through 2010]
 2.5 million members each year
Study Sites
Increase in CT Use
CT use by Age and Year
Contributions of Imaging Tests to Rate of Testing
and Radiation Exposure
Imaging Exams per
1000 enrollees
N, %
1994
Total Radiation Exposure
per 1000 enrollees
mSv, %
2007
1994
2007
Angiography +
Fluroscopy
66
7%
66
4%
408
35%
357
13%
CT
47
5%
197
12%
342
30%
1,662
61%
MRI
18
2%
89
6%
Nuclear Medicine
22
2%
65
4%
136
12%
411
15%
Radiographs
704
70%
880
55%
271
23%
311
11%
Ultrasound
153
15%
294
18%
Annual (Cumulative) Effective Dose
1%
10%
Median
For each patient, each year, we summed radiation form all imaging examinations and described the
distribution in dose among those with the highest annual exposure
Summary of Results
 A quadrupling in CT
• From 47 to 197/1000 enrollees per year
• 10% annual growth
 Similar increases for other imaging modalities
• Quadrupling in MRI
• Doubling in ultrasounds and nuclear medicine
• No decrease in radiographs
 Annual imaging costs increased three-fold and by 2007 averaged ~$300
per person per year.
• Half of costs from CT and MRI
 Preliminary results from 2008-2010 shows rates may be starting to
plateau or possibly even coming down
Summary of Results
 In 1994, CT accounted for 5% of imaging and 30% of radiation
exposure
 In 2007, CT accounted for 12% of imaging and 61% of radiation
exposure
 In 2007, ~ 7% of enrollees received an annual radiation exposure of 10
mSv or higher
Pediatric Imaging
Study of Imaging Use
 Retrospective observational study
 7 integrated healthcare systems
 1994-2010 (some sites only until 2007)
 Ages 14 years or younger
 169,000 – 511,000 children per year
Study Sites
20
07
5
20
06
10
20
05
20
04
20
03
20
02
20
01
20
00
19
99
19
98
19
97
19
96
19
95
19
94
Rate per 1,000 children
CT use in Children
35
30
25
20
15
<1 year
1-4 years
5-14 years
0
Body Areas Imaged with CT
1994
100%
2007
0%
100%
5%
14%
80%
3%
17%
80%
6%
8%
7%
4%
20%
40%
60%
60%
100%
40%
76%
71%
40%
65%
20%
20%
0%
0%
< 1 year
1-4 years
5-14 years
79%
47%
< 1 year
1-4 years
5-14 years
Other
Extremity
Spine
Chest
Abdomen
Head
Radiation Doses from Common CTs
 Data abstracted on 1,266 exams from three sites:
• Group Health Cooperative, Washington
• Kaiser Permanente Hawaii
• Kaiser Permanente North West, Oregon
 Sample
• 1994-2008
- One site collected additional data from 2009-2010
• Ages < 1 year – 30 years
 Randomly selected CT exams performed on:
• Head (brain, face, orbit)
• Abdomen/Pelvis
• Chest
• Spine or Neck
 Abstracted dose values from all CTs on same child on same day
Calculation of Effective and Bone Marrow Doses
and Leukemia Risk
 Doses calculated by Choonsik Lee PhD, Investigator, Radiation
Epidemiology Branch, NCI
 Developed improved methods
• Multiple phantom sizes
• Newborn, 1, 5, 10, 15, adult
• Male and female representing 50th percentile body size
• Improved phantom anatomy and skeleton dosimetry method
 Organ doses estimated from a precalculated dose matrix covering
whole body with a series of continuous axial slices of 1cm thickness.
 Hybrid phantom series coupled with Monte Carlo modeling of Siemens
sensation 16 were used to generate the precalculated dose matrix.
 Machine-specific CTDIw used to convert Siemens sensation 16 dose to
other machines.
 Estimated RR of death from leukemia 5 years after exam, based on
bone marrow dose (based on BEIR VII)
Relative Risk of Leukemia Death 5 years
after CT Exam
Number
of CTs
Min
5th
25th
50th
75th
95th
Max
≥ 2.0
≥ 3.0
< 1 year
87
1.1
1.2
1.4
1.6
2.0
2.6
3.8
24.0%
3.4%
1 year
52
1.1
1.1
1.3
1.5
1.8
2.5
2.7
9.6%
0%
2 – 4 years
144
1.1
1.1
1.2
1.3
1.5
2.0
2.6
5.6%
0%
5 – 9 years
246
1.0
1.0
1.1
1.2
1.3
1.5
2.2
0.8%
0%
10 – 14 years
308
1.0
1.0
1.0
1.1
1.1
1.2
1.8
0%
0%
Age Group
Summary of Pediatric Imaging
 CT use quintupled: from 11 to 52 CTs / 1,000 children per year
 Doses decreased until 2002, then in 2005, increased
• May be coming back down
 Doses and cancer risk higher for infants and toddlers
• Over 10% of children 4 years or younger received an effective dose of ≥20mSv
from one exam
• Many children have repeat testing
- Among children with ≥1 CT, the % with >1 CT in a year increased from 20%
in 1998 to 42% in 2006-2008
 Many exams resulted in more than a doubling of risk of dying from leukemia 5
years after exam
• 1 in 5 children <1 year
• 1 in 10 children 1 year
• 1 in 20 children 2-4 years
Discussion and
Conclusions
Factors Contributing to Increased Advanced
Medical Imaging Use
 Improvements in technology
 Increased capacity
 Patient demand – no perceived disincentive
 Physician demand
• Easy
• Lack of tolerance for ambiguity
• Limited evidence-based guidelines (or any guidelines)
 Malpractice concerns – leads to defensive imaging
 High profitability – self-referral
How to Reduce Radiation Exposure
 Reduce the number of studies: shared responsibility
• Make sure test hasn’t already been done
• Need evidence-based guidelines
 Reduce doses per test:
• Standard protocols
• Dose reference levels
 Educate physicians and technologists on importance of reducing dose
 Educate patients and providers about risks & benefits of imaging
 Directly assess the risks /benefits of CT to inform practice
Conclusions
 Medical Imaging is an integral component of medical care
 However, there are few evidenced based guidelines about when to
image, and the default is to over-image
 More widespread efforts needed to reduce dose, especially in children,
by
• Reducing unnecessary exams
• Reducing dose when imaging necessary
 Research is desperately needed to determine when to image, and how
to do so using lowest possible doses