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MAY 2012 | Volume 35 • Number 5
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Diagnostic Medical Imaging
Radiation Exposure and Risk
of Development of Solid and
Hematologic Malignancy
Peter D. Fabricant, MD; Marschall B. Berkes, MD;
Christopher J. Dy, MD, MSPH; Eric A. Bogner, MD
educational objectives
As a result of reading this article, physicians should be able to:
1. Understand the research used to govern safe radiation exposure doses.
2. Understand recent initiatives in decreasing radiation exposure.
3. Review specific techniques that may help decrease radiation exposure in
the daily practice of orthopedic surgery.
4. Gain perspective on spectrum of doses of ionizing radiation from common
imaging modalities.
Abstract
Limiting patients’ exposure to ionizing radiation during diagnostic imaging is of concern to patients and clinicians. Large singledose exposures and cumulative exposures
to ionizing radiation have been associated
with solid tumors and hematologic malignancy. Although these associations have
been a driving force in minimizing patients’
exposure, significant risks are found when
diagnoses are missed and subsequent
treatment is withheld. Therefore, based on
epidemiologic data obtained after nuclear
and occupational exposures, dose exposure limits have been estimated. A recent
collaborative effort between the US Food
and Drug Administration and the American
College of Radiology has provided information and tools that patients and imaging
professionals can use to avoid unnecessary
Drs Fabricant, Berkes, and Dy are from the Department of Orthopaedic Surgery, and Dr Bogner is
from the Department of Radiology, Hospital for Special Surgery, New York, New York.
The material presented in any Vindico Medical Education continuing education activity does not
necessarily reflect the views and opinions of Orthopedics or Vindico Medical Education. Neither
Orthopedics nor Vindico Medical Education nor the authors endorse or recommend any techniques,
commercial products, or manufacturers. The authors may discuss the use of materials and/or products
that have not yet been approved by the US Food and Drug Administration. All readers and continuing
education participants should verify all information before treating patients or using any product.
Correspondence should be addressed to: Peter D. Fabricant, MD, Hospital for Special Surgery,
Department of Orthopaedic Surgery, 535 E 70th St, New York, NY 10021 ([email protected]).
doi: 10.3928/01477447-20120426-11
415
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ionizing radiation scans and ensure use of
the lowest feasible radiation dose necessary
for studies. Further collaboration, research,
and development should focus on producing technological advances that minimize
individual study exposures and duplicate
studies. This article outlines the research
used to govern safe radiation doses, defines
recent initiatives in decreasing radiation exposure, and provides orthopedic surgeons
with techniques that may help decrease radiation exposure in their daily practice.
D
iagnostic imaging technology has
advanced significantly since the
introduction of the radiograph by
Wilhelm Röntgen in 1895.1 At that time,
little was known about the harmful effects
of radiograph beam radiation, and accidental exposures served as hard lessons in
the consequences of exposure. Following
Röntgen’s development of the radiograph,
Thomas Edison attempted to use the radiograph tube to develop an illuminating
lamp but soon discovered that his assistant
developed alopecia and skin ulcerations
and subsequently died of metastatic carcinoma in 1904.2
Large single-dose exposures and cumulative exposures have been associated with solid tumors and hematologic
malignancy. Over the past 100 years,
multiple cohorts of exposed populations
have been examined for dose–response
relationships between radiation exposure
and malignancy, and these historical data
have been used to determine harmful and
lethal doses and have subsequently helped
establish personal and occupational exposure limits.
Since the discovery of radiographs,
ionizing (eg, radiography, fluoroscopy,
and computed tomography [CT] scan)
and nonionizing (eg, ultrasound and magnetic resonance imaging) modalities have
emerged. Patient safety remains a priority
with these newer imaging modalities. Due
to their frequent use and the higher dose
of ionizing radiation, CT scans are of the
highest concern. Exposure is common,
416
and therefore the at-risk population is
large, owing to the fact that 72 million CT
scans are performed in the United States
each year, and the rate has increased 12%
annually from 1993 to 2007.3 As of 2007,
medicine represented the largest source
of ionizing radiation exposure to the US
population4 and has been reported to be
the single largest manmade population
exposure, affecting nearly everyone who
seeks medical care.5 Appearance of this
information in popular media created a
scare among patients and brought the issue of CT scanning overuse and radiation
exposure to the forefront of the medical
lay press.6,7
Although associations between ionizing radiation and increasing frequency of
CT scanning have been a driving force in
minimizing patients’ exposure to ionizing
radiation, significant risks occur when
diagnoses are delayed or missed and subsequent treatment is withheld due to fears
of radiation exposure. Overexposure to
ionizing radiation and missed diagnoses
have large economic and biopsychosocial
consequences, affecting patients, families,
and the medical system. Maximizing patients’ benefits and minimizing potential
harm involves judicious use of radiological studies, use of nonionizing radiation
modalities whenever possible, and properly dosing ionizing radiation when needed to maximize study resolution without
delivering excessive radiation doses. This
article outlines the research used to govern safe radiation doses, defines recent
initiatives in decreasing radiation exposure, and provides orthopedic surgeons
with specific techniques that may help
decrease radiation exposure in their daily
practice.
Current Research
Several obstacles exist when attempting to study the effects of ionizing radiation on humans. Ionizing radiation is carcinogenic in humans and teratogenic in
fetuses. Because there is, by definition, no
safe dose to administer for human testing,
experimental human study designs are
unethical, and information gleaned from
animal studies is limited due to their dissimilar genome and physiology compared
with those of humans. Therefore, limited
pure biologic evidence exists, but animal
studies support the view that low-dose radiation acts principally on the early stages
of tumorigenesis, and a dose-dependent
relationship exists between radiation dose
and induction of DNA damage in cells.8
No large-scale epidemiologic study of
cancer induction by diagnostic radiation is
reported in the literature.9 Therefore, the
greatest amount of information regarding
human exposure to radiation is from studies of atomic-bomb survivors, which provide the ability to calculate dose-response.
Many advantages are found in studying
this population: a large number of participants (120,321 in the original Life Span
Study [LSS] cohort), inclusion of both
sexes, a varied array of dose ranges, and
total body exposure, which allows for assessment of cancers at various body sites.8
Although medical radiation studies, occupational exposures, and environmental
studies have also provided some insight,
the LSS cohort is the most robust cohort
of clinical participants.
Samartzis et al10 reviewed the LSS
cohort to determine threshold exposures
for the development of radiation-induced
bone sarcoma. They analyzed 80,181 participants and determined a threshold dose
of 0.85 Gy using Poisson regression. The
most common tumor was pelvic osteogenic sarcoma. Survival in these patients
was low, with a 5-year mortality rate of
75%. The same cohort has also been
analyzed for increased incidence and radiation threshold of nonmusculoskeletal
tumors.11 Hematologic malignancy rates
were higher than those seen in the general
population, including leukemia and lymphoma. In total, 34% of leukemia deaths
were attributable to radiation exposure in
survivors exposed to .0.005 Gy.11
A meta-analysis by Daniels and
Schubauer-Berigan12 evaluated 23 pri-
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mary research investigations that assessed
occupational protracted exposures to lowdose ionizing radiation and calculated an
excess relative risk of leukemia of 0.19 at
0.1 Gy. This is lower than that noted in the
LSS cohort but can be explained by differences in exposure types: single-event
vs chronic protracted exposure. Further
epidemiological data suggest that acute
exposures are 2 to 5 times more potent on
increased cancer risk in humans than protracted exposures.13
Li et al14 evaluated the LSS cohort for
solid and hematologic malignancies and
noted an incidence of 17.2% for solid tumors, 0.35% for leukemias, and 0.52% for
lymphomas and myelomas. All cancers
studied (ie, gastric, lung, colon, liver, female breast, thyroid, bladder, lymphoma,
and leukemia) noted a threshold value of
0.005 Gy, with varying increases in relative risk with levels above that threshold.
Malignancies most sensitive to radiation
dose were those with greater increases in
relative risk for dose exposures .0.005
Gy, and included lung, colon, female
breast, thyroid, bladder, and leukemia.
These data were corroborated by Preston
et al,15 who noted that 11% of solid tumors
in participants exposed to .0.005 Gy
could be attributed to radiation exposure,
with increasing relative risk in a dose–response relationship. They also noted a decrease in excess relative risk of 17% per
decade increase in age at exposure when
controlling for age at diagnosis, and an
increase in excess relative risk throughout the study period when controlling for
age at exposure, indicating that radiationassociated increases in cancer rates persist
throughout life regardless of age at exposure. When evaluating nonsex-specific
cancers, no sex differences existed in rates
of malignancy.
Studies of the LSS cohort have produced robust evidence that exposure to
ionizing radiation .0.005 Gy (5 mSv)
confers an increased risk of solid and
hematologic malignancy, with a dosedependent increase in relative risk. Bone
MAY 2012 | Volume 35 • Number 5
tumors have a higher exposure threshold
of 0.85 Gy (850 mSv) prior to excess
relative risk. Estimates of excess relative
risk from the LSS cohort are higher than
those from studies examining participants with protracted low-dose exposure,
and therefore may lead to an overestimate of the LSS studies on cancer risk.
Radiation-associated increases in cancer
rates persist throughout life regardless
of age at exposure, and earlier exposure
is associated with increased excess relative risk of developing radiation-induced
malignancy during one’s lifetime. Given
these data, risk of malignancy increases in
a dose-dependent manner. Therefore, it is
important to determine current patient exposures from diagnostic radiology studies
and identify potential methods of decreasing patient exposure.
Fazel et al16 analyzed utilization data
from 952,420 participants aged between
18 and 64 years to determine average annual radiation exposure doses. Median effective dose was 0.1 mSv per participant
per year. Cumulative effective doses increased with advancing age and were higher in women than in men. Interestingly, CT
scans accounted for 75.4% of exposure,
with 81.4% of those being administered
in the outpatient setting. In total, 80% of
men and 78% of women were exposed to
no or low doses (0-3 mSv) of radiation annually. Although a significant minority of
participants were exposed to higher doses
of radiation, they were typically elderly
patients.16 Table 1 shows the average dose
of various imaging procedures that use
ionizing radiation. Plain radiography creates less exposure than fluoroscopy (continuous radiograph) or CT scanning, with
interventional procedures generating the
greatest exposures. For comparison, Table
2 lists sources of background radiation
and average effective dose.18 Extremity
radiography exposes patients to 1/3000 of
yearly background radiation and 1/1000
of the radiation exposure of a round-trip
transcontinental flight. Fluoroscopic and
CT examination exposures are greater
Table 1
Common Musculoskeletal and
Medical Imaging Procedures
and Corresponding Average
Effective Dosea
Average
Effective
Exposure, mSv
Study
Myocardial perfusion
imaging
15.6
Chest (noncoronary)
CT angiography
15
Percutaneous coronary
intervention
15
Abdomen CT
8
Chest CT
7
Nuclear bone imaging
6.3
Cervical spine CT
6
Lumbar spine CT
6
Pelvis CT
6
Neck CT
3
Head or brain CT
2
Thyroid uptake
1.9
Lumbar spine
radiography
1.5
Abdomen radiography
0.7
Mammography
0.4
Chest radiography
Extremity radiography
0.1-0.02
0.001
Abbreviation: CT, computed tomography.
a
Adapted from Mettler et al4 and the
American College of Radiology and
Radiological Society of North America.17
Table 2
Background Radiation Sources
and Average Effective Dose18
Source
Average
Effective
Exposure, mSv
Cosmic radiation/
background
3
Radon gas
2
Living at plateau/
altitude
11.5
Coast-to-coast
round-trip flight
10.03
417
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and, therefore, of higher clinical concern
with repeated studies.
Children’s exposure to ionizing radiation is an elevated concern given their developing physiology and increased risk of
lifetime malignancy with early radiation
exposure. The use of CT scans in children
has increased rapidly and has been primarily driven by the speed with which a
scan can be performed (within a matter of
seconds), which essentially eliminates the
need for anesthesia to limit motion during
imaging.19 Adult and pediatric victims of
blunt trauma routinely undergo intense
imaging in the emergency room and trauma bay to facilitate rapid diagnosis.
To determine pediatric exposure in a
cohort of blunt trauma patients, Mueller
et al20 prospectively studied all pediatric
(aged 0-17 years) blunt trauma patients
presenting at a major tertiary care urban
medical center emergency department.
Dosimeters were placed on reproducible
anatomical landmarks of all children prior
to initial CT evaluation. Mean wholebody effective dose was 17.43 mSv, which
falls within the range of historical doses
correlated with an increased risk of leukemia and solid tumors.14,15 Although an
increased risk of future malignancy exists,
the emergent nature of obtaining an accurate and rapid diagnosis for the presenting
pediatric trauma patient outweighs such
future risk because the consequences of
misdiagnosis can be immediately fatal.
Clearly, obstacles exist in conducting
meaningful research in this field despite
its ubiquitous importance. Again, because
it is unfeasible and unethical to conduct
directed human research by exposing
participants to radiation, studies largely
comprise epidemiologic data from atomic-bomb survivors (eg, the LSS cohort),
occupational exposures, and observational studies. All methods have strengths
and weaknesses. Although the LSS cohort includes patients of varying ages and
both sexes, exposures are estimated and
acute exposures may overestimate the effect that would be seen with protracted
418
low-dose exposures. Observational studies typically have fewer participants and
smaller exposures, but dosimetry allows
for more accurate and precise dose measurements. Experimental designs in animals are limited by the genetic and physiologic differences between humans and
animals. Regardless of research methodology, it is accepted that ionizing radiation
is carcinogenic and that a dose–response
relationship exists between exposure and
several types of malignancy.
Future Direction
It is in the best interest of physicians
and patients to minimize exposure to ionizing radiation. However, studies requiring
the use of ionizing radiation are clinically
necessary and allow for rapid, accurate
diagnosis of various disease entities and
traumatic conditions. Therefore, future research should be directed toward reducing
ionizing radiation as much as is clinically
reasonable. As technology emerges, practice guidelines should be updated based on
scientific study of new imaging modalities
and scanner protocols. Joint efforts between the American College of Radiology
and the US Food and Drug Administration,
called Image Wisely (in adults) and Image
Gently (in children), have initiated educational efforts of patients, families, radiologists, and radiology technicians in an
attempt to eliminate unnecessary radiation exposure in patients and health care
workers.21-23 Minimizing excessive radiation exposure involves using a dose as low
as reasonably achievable to obtain proper
resolution and therefore prevent the need
for repeat imaging. Lead shielding of radiosensitive body parts, collimation (restricting beam area), patient positioning,
exposure time during fluoroscopy, and
appropriate safety training of all radiology
technologists are also imperative.9
Research and development of new technology has the potential to achieve higher
image resolution with minimal radiation
dose. For example, diagnostic workup of
certain bony hip abnormalities requires
3-dimensional rendering of bony structures.24 Previously, routine pelvic CT scans
were used to obtain these images, and orthopedic surgeons analyzed bony structures
while the increased radiation dose used to
obtain soft tissue resolution was wasted.
Early intrainstitutional collaboration
between treating orthopedic surgeons and
radiologists led to the development of lowdose CT scanning protocols that allow the
surgeon to gain comprehensive diagnostic
information while using minimal radiation
exposure. According to personal communication with D. Gallagher, RT, in 2011, this
has led to a pelvic CT scanning protocol
that gains 3-dimensional imaging of a CT
scan while using 2.5 mSv, or the equivalent
dose of 4 to 6 pelvic radiographs. This underscores a vital need for an open dialogue
between treating physicians, radiologists,
and patients and their families regarding
the goals of diagnosis and treatment. In
addition, early private-sector research has
developed CT scanning protocols that minimize radiation by 40% while maintaining
a similar level of diagnostic resolution.25
This leads to more desirable software and
equipment that can competitively enter the
market, further driving industry research
and innovation that benefits patients.
Additional future areas of research
should include practical and accessible
methods of image portability. A universal imaging display language and accessible electronic medical records would
eliminate the need for repeat imaging
if patients do not possess their imaging
studies. A complete log of cumulative
year-to-date and lifetime radiation exposures would allow patients and physicians
to make more informed decisions “on the
margin” regarding the risk–benefit ratio of
further imaging, given the patients’ cumulative dose from multiple studies across
multiple practitioners.
Minimizing Radiation Exposure:
Practical Considerations
Through the use of advanced diagnostic technology, improved operating room
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instrumentation, proper safety principles,
and rational decision making, orthopedic
surgeons can decrease the amount of radiation exposure to themselves, patients,
and ancillary medical staff. The easiest
and least expensive way to reduce radiation exposure in the operating room is to
use standard radiation safety precautions. This involves using the low-dose
or pulsed fluoroscopy (rather than extended exposures) to obtain an adequate
quality image, which has been shown to
dramatically reduce exposure to ionizing
radiation.26 Similarly, a mini C-arm fluoroscopy unit can be used in lieu of a standard C-arm for intraoperative extremity
fluoroscopy when feasible, which releases
a lower dose of ionizing radiation.27 Also,
the effective dose received by the operating room staff or patient can be dramatically reduced if they are located at least 36
inches away from the beam.28 Therefore,
it is recommended that all nonessential
staff remain at least 36 inches away from
the radiation source during fluoroscopic
exposure. Proper safety equipment, including radiation safety gowns, thyroid
shields, gloves, and radiopaque glasses,
should be used habitually.29
Advances in surgical instrumentation
can also lead to less ionizing radiation in
the operating room. For instance, a large
number of fluoroscopic images are often
required to appropriately place interlocking screws through an intramedullary
device via the perfect circles technique.
However, several readily available devices
largely decrease the need for fluoroscopy
for this surgical technique, including a
mechanical aiming arm, which affixes
to an intramedullary nail proximally and
allows for accurate placement of distal
interlocking screws.30,31 In addition, techniques using computer navigation and
electromagnetic field guidance have been
developed to eliminate the use of fluoroscopy for interlocking screw placement.32
Computer navigation has also been
well described for several orthopedic
procedures. This technology allows for
MAY 2012 | Volume 35 • Number 5
increased surgical precision with less reliance on intraoperative fluoroscopy use
and, therefore, decreased radiation exposure. Studies have shown that navigation can dramatically reduce fluoroscopy
time during spine surgery when pedicle
screw instrumentation is performed.33,34
In addition, navigation has also been described for retrograde drilling of osteochondral lesions, eliminating the need for
fluoroscopic radiation.35 This reduction in
intraoperative fluoroscopy use is particularly important when dealing with pediatric patients, and posterior spinal fusions
with pedicle screw instrumentation and
osteochondral lesion drilling are common
procedures in the pediatric population that
would benefit greatly from a reduction in
ionizing radiation exposure.
Finally, patients’ exposure to ionizing
radiation can be reduced through rational
clinical decision making. Surgeons must
ask themselves, “Is this radiograph really necessary?” Some recent publications
have suggested that radiography use can
be limited without negative diagnostic
or clinical consequences. For instance,
the standard workup for nonaccidental
trauma involves a skeletal survey of the
entire body and a follow-up survey a few
weeks after the initial encounter. Sonik et
al36 reported that no new fractures of the
skull, spine, or pelvis had been detected
in the follow-up survey based on their
series and data from the literature. From
this, it can be inferred that routine repeat
imaging of the skull, spine, and pelvis is
unnecessary unless a high clinical suspicion of injury exists; this is especially
important because these anatomic areas
receive the highest amount dose exposure,
compared with the extremities. Another
example is the use of immediate postoperative pelvis radiographs following total
hip arthroplasty. The standard practice in
many institutions is to obtain an immediate radiograph of the pelvis in the operating room or recovery room to rule out
dislocation or periprosthetic fracture. Ndu
et al37 reported that, in a series of 632 re-
covery room radiographs following total
hip arthroplasty, 17% of radiographs were
inadequately performed. In addition, only
1.9% (12 of 632) identified technical issues, of which only 0.3% (2 of 632) required intervention; 1 was a dislocation
diagnosed by clinical examination prior
to the radiograph being taken.37 Based on
these data, immediate postoperative radiographs may be avoided given the unnecessary economic and health burden associated with their use.
Conclusion
It is important to balance the immediate, frequently substantial clinical need
for radiological studies and procedures
against the rare but significant risk of cancer that would not be evident for years, if
at all.16 Current research and policies by
radiological societies and governmental
organizations have brought these concerns
to the forefront. Future research should
focus on developing technology that allows for improved diagnostic accuracy
with less radiation, as well as developing
systems-based approaches to image and
medical record portability to eliminate duplicate imaging studies. For the time being, orthopedic surgeons should use the
techniques outlined in this article to minimize radiation exposure to themselves,
patients, and medical staff.
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