Download Radiation Safety Issues

4/5/2011
Objectives
 Discuss patient safety issues related to ionizing
radiation in medical imaging.
imaging
 Discuss the concept of ALARA (as low as reasonably
achievable).
Glynda Ramsey, M.D.
Mountain Empire Radiology, PC
March 30, 2011
Ionizing Radiation 1

Effective Dose 2
 X-rays are ionizing radiation.
 X-rays have sufficient energy to remove electrons from
their orbits and create highly reactive ions, known as
“f
“free
radicals.”
di l ”
 Free radicals react with adjacent tissue and lead to
damage of DNA.
 X-rays can ionize DNA directly.
 Much of the radiation induced damage is repaired by
cellular mechanisms.
 When repair is incomplete, or “misrepair” occurs, the
 Different tissues and organs have varying sensitivity to
radiation exposure.
 The actual dose to different organs varies, depending on
the radiosensitivity of the specific organ.
 The term effective dose is used when referring to the dose
averaged over the entire body.
 The effective dose accounts for the relative sensitivities
of the different tissues exposed.
genetic damage can lead to the induction of cancer.
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Effective Dose 2
Naturally-Occurring “Background"
NaturallyRadiation Exposure 4
 We are continuously exposed to radiation from natural
 Use of effective dose allows for:
 quantification of risk
 comparison to more familiar sources of exposure, including
natural background radiation. 2
 The scientific unit of measurement for radiation dose,
commonly referred to as effective dose, is the millisievert
(mSv). 4
Comparison of Medical Imaging to
Background Radiation 4
 The radiation dose of one chest x-ray (0.1 mSV), is
equivalent to the amount of radiation exposure one
receives from the natural surroundings in 10 days.
days
 Background radiation has not changed since 1980,
but Americans' total per capita radiation exposure
has nearly doubled. The main reason is increased use
of medical imaging.
sources, referred to as “background radiation.”
 The average
g p
person in the U.S. receives an effective dose of
3 mSv per year from background radiation.
 Background doses vary. People living in the plateaus of
Colorado and New Mexico receive 1.5 mSv more
radiation per year than those living at sea level.
 The largest source of background radiation comes from
radon gas in our homes (approximately 2 mSv annually).
Other sources include cosmic radiation and terrestrial
sources of uranium.
Increasing Use of Medical
Radiation
 The proportion of total radiation exposure that comes
from medical sources has grown from 15% in the early
,
1980s to more than 35% - 50% today.
today 2,3
 CT alone accounts for 24% of all radiation exposure in
the United States.2
 Nuclear medicine procedures account for 12%. 3
 Radiation dose per person from medical X-rays has
increased almost 500 percent since 1982. 3
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4/5/2011
Increasing Use of CT
 The total number of CT examinations performed
annually in the United States has risen from
approximately 3 million in 1980 to nearly 70 million in
2007 5
2007.
 The largest increases in CT use have been in the
categories of pediatric diagnosis and adult screening. 1
 Adult screening exams include:




CT colonography (virtual colonoscopy)
CT lung screening for current and former smokers
CT cardiac screening (calcium scoring and CTA)
CT whole-body screening, including PET/CT 1
Estimate of CT Overutilization 1
 From an individual standpoint, when a CT scan is
j
justified
by
y medical need,, the associated risk is small
relative to the diagnostic information obtained.
 “If it is true that one third of all CT scans are not
justified by medical need (Slovis, Ped Rad 2002),
perhaps 20 million adults and, crucially, more than 1
million children per year in the United States are being
irradiated unnecessarily.” -Brenner
Estimates of Radiation Induced
Cancer from CT 1
 Most diagnostic CT scans are associated with very favorable
benefit to risk ratios. The individual risk estimates are small.
 Small individual risks applied to increasing use ithroughout
the population may create a public health issue some years in
the future.
 Based on data from 1991 through 1996, it is estimated that
0.4% of all cancers in the U.S. may be attributable to radiation
from CT.
 Adjusting this estimate for current (2007) CT use, the estimate
might now be in the range of 1.5 to 2.0% of all cancers.
Increasing CT Use
in Children 1
 Estimates of the proportion of CT studies that are
currently performed in children range between 6% and
11%.
11%
 The growth of CT use in children has been driven
primarily by the decrease in the time needed to perform
a scan, largely eliminating the need for anesthesia.
 The major growth area in CT use for children has been
presurgical diagnosis of appendicitis, for which CT
appears to be both accurate and cost-effective.
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Increased Radiation Risk
in Children 1
 For a given mAs setting, pediatric doses are much
larger than adult doses.
 A child's thinner torso provides less shielding of organs
from the radiation exposure.
 The mAs setting should be reduced for children to
reduce the dose and the risk (dose modulation).
 Optimally, each patient’s CT protocol should be
Increased Radiation Risk
in Children 1
 Cancer risks decrease with increasing age.
 Children have more years of life during which a
potential cancer can be expressed (latency periods for
solid tumors are typically decades).
 Growing children are inherently more radiosensitive,
since they have a larger proportion of dividing cells.
tailored to the clinical question and the body size and
habitus.
Lifetime Attributable Risk 6
 Lifetime attributable risk (LAR) is defined as additional
cancer risk above the baseline cancer risk for the
population It is age adjusted.
population.
adjusted
 7th National Academy of Science report on Biological
Effects of Ionizing Radiation (BEIR VII Phase 2,
published 2006) provides a method to estimate LAR of
cancer based on a single radiation exposure and a patient's
age at the time of that exposure.
 LAR is an average risk for the general population.
Lifetime Attributable Risk 8
Several factors contribute to each individual’s radiation dose and risk:
 Body habitus (size and weight) – more dose for obese patients
 Body part (target organ) – variable organ sensitivity
 Age at exposure – more risk at younger age
 Type of equipment and protocol
 64 slice helical less risk than 4 slice
 Single phase less than multiphase
 Z axis, scan plane
 Shields (breast, gonad, thyroid)
 ?Cumulative dose – BEIR VII estimates risk for a single radiation exposure
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Correlation of BEIR VII Results
 There was a significant increase in the overall risk of
cancer in the subgroup of atomic
atomic-bomb
bomb survivors who
received low doses of radiation, ranging from 5 to 150 mSv;
the mean dose in this subgroup was about 40 mSv. 6
 This dose approximates the relevant organ dose from a
typical CT study involving two or three scans in an adult
(CT abdomen and pelvis with and without contrast ~
32mSv).
Estimates of Radiation Induced
Cancers from CT 7
Lifetime Attributable Risk 6
 BEIR VII indicated that a single population dose of 10
mSv (one CT abdomen and pelvis) is associated with a
lifetime attributable risk (LAR) of 1 in 1000 for
developing a solid cancer or leukemia.
 The overall risk of developing a solid cancer or
leukemia from all causes would be 420 in 1000 (42%).
 The BEIR VII reports the risk in children (exposed to
10 mSv dose) is 1 in 550.
Estimates of Radiation Induced
Cancers from CT 7
 Approximately 29,000 future cancers could be related to CT
scans performed in the US in 2007
 Largest contributions were from scans of the:
 Abdomen and pelvis (n = 14 000)


Greater number of scans
Radiosensitivity of digestive tract
 33% of the p
projected
j
cancers were due to scans
performed at the ages of 35 to 54 years
 15% due to scans performed at ages younger than 18 yrs
 66% were in females
 Chest (n = 4100))
 Head (n = 4000)
 Chest CT angiography (n = 2700)
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Major Risk Factors for Radiation
Induced Cancer –Dose and Age 8
Estimated Risk of Coronary CT
Angiography 9
 The highest organ LARs were for lung cancer and, in
 An estimated 1 in 270 women who underwent CT
coronary angiography at age 40 years will develop
cancer from that CT scan, and 1 in 600 for men
 An estimated 1 in 8100 women who had a routine head
CT scan at age 40; 1 in 11,080 men
 For 20-year-old patients, the risks were approximately
doubled, and for 60-year-old patients, they were
approximately 50% lower.
younger women, breast cancer. Organ doses:
 42 to 91 mSv for the lungs
 50 to 80 mSv for the female breast
 Lifetime cancer risk estimates for standard cardiac scans:

1 in 143 for a 20-year-old woman

1 in 3261 for an 80-year-old man
 Estimated cancer risks using ECTCMX (x-ray controlled by EKG)
 1 in 715 for 60-year-old woman
 1 in 1911 for 60-year-old man
Overutilization of CT
 “There is a considerable literature questioning the use of CT,
or the use of multiple CT scans, in a variety of contexts,
including management of blunt trauma,
trauma seizures,
seizures and chronic
headaches, and particularly questioning its use as a primary
diagnostic tool for acute appendicitis in children.” - Brenner 1
 “But beyond these clinical issues, a problem arises when CT
scans are requested in the practice of defensive medicine, or
when a CT scan, justified in itself, is repeated as the patient
passes through the medical system, often simply because of a
lack of communication.” - Brenner 1
ALARA
“As Low As Reasonably Achievable”
Make every effort to maintain exposures to ionizing
radiation as low as possible.
 What information is needed for clinical
management?
 How will this exam alter your management?
 Will the benefits outweigh the risks?
 Eliminate an invasive procedure
 Incidental findings may require follow-up or
intervention
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4/5/2011
ALARA
“As Low As Reasonably Achievable”
Clinical Application of ALARA
 Will another test (with less or no radiation) provide
similar clinical information?
 Keep track of how many imaging procedures you
order on each patient
 Re-examine standard follow up regimens for chronic
disease; can time between scans be extended?
 Discourage diagnostic imaging that is not medically
indicated (”worried well”).
Clinical Application of ALARA
A 26 year old female presents with colicky left flank pain and
gross hematuria. She has previously passed two kidney stones and
i currently
is
l afebrile
f b il with
i h normall WBC.
WBC She
Sh states the
h pain
i is
i
similar to the previous kidney stones. Is a diagnostic imaging test
necessary to initially treat this patient?
A 26 year old female presents with colicky left flank pain and
gross hematuria. She has previously passed two kidney stones and
i currently
is
l afebrile.
f b il She
Sh states the
h pain
i is
i similar
i il to the
h previous
i
kidney stones. Is a diagnostic imaging test necessary to initially
treat this patient?
 No exam necessary
 CT abdomen without contrast (stone protocol)
 CT abdomen with and without contrast (triple phase)
Clinical Application of ALARA
A 26 year old female presents with colicky left flank pain and
gross hematuria. She has previously passed two kidney stones and
i currently
is
tl febrile.
f b il It iis necessary tto d
determine
t
i whether
h th hi
high
h grade
d
obstructiona and hydronephrosis are present. What imaging test
would utilize the least amount of ionizing radiation?
 0 mSv No exam necessary
 Non-contrast CT abdomen and pelvis (stone protocol)
 16 mSv CT abdomen and pelvis without contrast (stone protocol)
 Ultrasound of kidneys and urinary bladder
 16- 24 mSv CT abdomen with and without contrast (triple phase)
 CT abdomen with and without contrast ( dual or triple phase)
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Criteria for Lifetime Risk of
Fatal Cancer in an Adult 6
Clinical Application of ALARA
A 26 year old female presents with colicky left flank pain and
gross hematuria. She has previously passed two kidney stones and
i currently
is
tl febrile.
f b il It iis necessary tto d
determine
t
i whether
h th hi
high
h grade
d
obstructiona and hydronephrosis are present. What imaging test
would utilize the least amount of ionizing radiation?
 Risk of cancer (fatal and nonfatal) for general population 1/2.4
 Risk of fatal cancer for general population 1/5
 Negligible
 16 mSv Non-contrast CT abdomen and pelvis (stone protocol)
 0 mSv Ultrasound of kidneys and urinary bladder
 24 mSv CT abdomen with and without contrast (triple phase)
Imaging Procedures and Their
Approximate Radiation Doses 2,4
1/1,000,000
 Minimal
1/1,000,000 – 1/100,000
 Very low
1/100,000 – 1/10,000
 Low
1/10,000 – 1/1000
 Moderate
1/1000 – 1/500
Imaging Procedures and Their
Approximate Radiation Doses
Procedure
Procedure
Avg effective
Range in
dose ((mSv)) literature ((mSv))
0.001
0.001–0.035
Compared to
Background
g
3 hrs
Avg effective
Range in
dose (mSv) literature (mSv)
Compared to
Background
Estimated
Risk
Estimated
Risk

X ray lumbar spine
X-ray,
15
1.5
05 18
0.5–1.8
6 mo
very low
negligible

CT, head
2
0.9–4
8 mo
very low
1.0–12
1 yr

Bone density test (DXA)

X-ray, arm or leg
0.001
0.0002–0.1
3 hrs
negligible

CT, cardiac calcium score 3

X-ray, panoramic dental
0.01
0.007–0.09
1 day
negligible

Nuclear bone scan
6.3
2 yr
low

X-ray, chest
0.1
0.05–0.24
10 days
minimal

UGI
6
2 yr
low

X-ray, abdominal
0.7
0.04–1.1
12 wks
very low

CT, spine
6
1.5–10
2 yr
low

Mammogram
0.4
0.10–0.6
7 wks
very low

CT, pelvis
6
3.3–10
2 yr
low
low
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4/5/2011
Imaging Procedures and Their
Approximate Radiation Doses
Procedure
Avg effective
Range in
dose (mSv) literature (mSv)
Compared to
Background
Estimated
Risk

C
Coronary
angio/stent
i /t t
7/15
2 yr/5yr
/5
l
low

CT, chest (single phase)
7
4.0–18
2 yr
low

CT, abdomen, wo/dual
8/16
3.5-16
3-5 yr
low

CT, abdomen multiphase
16-30
10 yr
moderate

BE
8
3 yr
low

CT, colonoscopy
10
3 yr
low
4.0–13.2
Imaging Procedures and Their
Approximate Radiation Doses
FDA Recommendation for
Patients 3
 Ask your health care professional how an X-ray will help.
How will it help find out what's wrong or determine your
treatment?
 Ask if there are other procedures that might be lower risk
but still allow a good assessment or treatment for your
medical situation.
 Don't refuse an X-ray. If your health care professional
explains why it is medically needed, then don't refuse an
X-ray. The risk of not having a needed X-ray is greater
than the small risk from radiation.
Procedure
Avg effective
Range in
dose (mSv) literature (mSv)
Compared to
Background
Estimated
Risk

VQ nuclear lung scan
3

Pulmonary CT angio
98
8.0–31

Coronary CT angio
16
5.0–32
5 yrs

CT, whole body
318
6-10 yrs
moderate

Nuclear cardiac stress test
13 yrs
moderate
20 or more
40
1 yr
low
3 yrs
low
low
FDA Recommendation for
Patients 3
 Don't insist on an X-ray. If your health care
professional explains there is no need for an X-ray,
then don't demand one.
one
 Tell the X-ray technologist in advance if you are, or
might be, pregnant.
 Ask if a protective shield can be used. If you or your
children are getting an X-ray, ask whether a lead apron
or other shield should be used.
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4/5/2011
FDA Recommendation for
Patients 3
 Ask your dentist if he/she uses the faster (E or F)
speed film for X-rays.
 It costs about the same as the conventional D speed
film and offers similar benefits with a lower
radiation dose.
 Using digital imaging detectors instead of film
further reduces radiation dose.
Medical Imaging Record 3
FDA Recommendation for
Patients 3
 Know your X-ray history.
 "Just as you may keep a list of your medications with
you when
h visiting
i i i the
h doctor,
d
keep
k
a list
li off your imaging
i
i
records, including dental X-rays," says Ohlhaber.
 When an X-ray is taken, fill out the card with the date
and type of exam, referring physician, and facility and
address where the images are kept.
 Show the card to your health care professionals to avoid
unnecessary duplication of X-rays of the same body part.
 Keep a record card for everyone in your family.
References
 1) Brenner DJ, Hall EJ. Computed tomography – an increasing source
of radiation exposure. N Engl J Med 2007; 357:2277-2284.
http://www.nejm.org/doi/full/10.1056/NEJMra072149#t=article
 2) Robb-Nicholson
R bb Ni h l
C.
C Ad
doctor
t ttalks
lk about
b t radiation
di ti risk
i k from
f
medical
di l
imaging. Harvard Women’s Health Watch. October 2010
https://www.health.harvard.edu/newsletters/Harvard_Womens_Healt
h_Watch/2010/October/radiation-risk-from-medical-imaging
 3) FDA Consumer Updates. Reducing radiation from medical x-rays.
http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095505.ht
m
 4) American College of Radiology and Radiologic Society of North
America. RadiologyInfo.
http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty
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4/5/2011
References
References
 5) Amis ES Jr, Butler PF, Applegate KE, et al. American College
of Radiology. American College of Radiology white paper on
radiation dose in medicine. J Am Coll Radiol. 2007;4(5):272-284.
 6) Committee on the Biological Effects of Ionizing Radiation.
Biological Effects of Ionizing Radiation (BEIR) VII: Health Risks
from Exposure to Low Levels of Ionizing Radiation. Washington
DC; National Academies Press; 2005.
http://books.nap.edu/catalog/11340.html.
 7) Berrington de Gonzalez A, Mahesh M, et al. Projected cancer
 8) Smith-Bindman R, Lipson J, Marcus R, et al. Radiation dose
associated with common computed tomography and the
associated lifetime attributable risk of cancer. Arch Int
Med.2009:169(22):2078-2086.
 9) Einstein AJ, Henzlova MJ, Rajagopalan S. Estimating risk of
cancer associated with radiation exposure from 64-slice computed
tomography coronary angiography. JAMA. 2007:298(3):317-23
(ISSN: 1538-3598)
risks from computed tomographic scans performed in the United
States in 2007. Arch Int Med. 2009:169(22):2071-2077.
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