The Journal of TRAUMA威 Injury, Infection, and Critical Care
Radiation Exposure From Diagnostic Imaging in Severely
Injured Trauma Patients
Homer C. Tien, MD, Lorraine N. Tremblay, MD, PhD, Sandro B. Rizoli, MD, PhD, Jacob Gelberg, BSc,
Fernando Spencer, MD, Curtis Caldwell, PhD, and Frederick D. Brenneman, MD
Background: Trauma patients often
require multiple imaging tests, including
computed tomography (CT) scans. CT
scanning, however, is associated with
high-radiation doses. The purpose of this
study was to measure the radiation doses
trauma patients receive from diagnostic
imaging.
Methods: A prospective cohort study
was conducted from June 1, 2004 to March
31, 2005 at a Level I trauma center in Toronto, Canada. All trauma patients who arrived directly from the scene of injury and
who survived to discharge were included.
Three dosimeters were placed on each patient (neck, chest, and groin) before radio-
logic examination. Dosimeters were removed before discharge. Surface doses in
millisieverts (mSv) at the neck, chest, and
groin were measured. Total effective dose,
thyroid, breast, and red bone marrow organ doses were then calculated.
Results: Trauma patients received a
mean effective dose of 22.7 mSv. The standard “linear no threshold” (LNT) model
used to extrapolate from effects observed
at higher dose levels suggests that this
would result in approximately 190 additional cancer deaths in a population of
100,000 individuals so exposed. In addition, the thyroid received a mean dose of
58.5 mSv. Therefore, 4.4 additional fatal
thyroid cancers would be expected per
100,000 persons. In all, 22% of all patients
had a thyroid dose of over 100 mSv (mean,
156.3 mSv), meaning 11.7 additional fatal
thyroid cancers per 100,000 persons
would result in this subgroup.
Conclusion: Trauma patients are exposed to significant radiation doses from
diagnostic imaging, resulting in a small
but measurable excess cancer risk. This
small individual risk may become a
greater public health issue as more CT
examinations are performed. Unnecessary
CT scans should be avoided.
Key Words: Radiation dosimetry,
trauma, cancer risk.
J Trauma. 2007;62:151–156.
T
he use of computed tomography (CT) has increased
dramatically during the past two decades. From 1981 to
1998, the number of CT scans performed annually in the
United States has increased nearly 10-fold.1 Of all the X-ray
based tests, CT contributes one of the highest radiation doses
to patients.2
Trauma patients in particular are at risk for high-dose
radiation exposure. Injured patients often receive multiple CT
scans and radiographs during their hospitalization.3 Injured
patients are also more susceptible to the effects of radiation
because they tend to be young in age.4 Radiation exposure
has been clearly linked to the development of cancer5 and the
young are much more prone to these effects than the elderly.6
Submitted for publication August 1, 2006.
Accepted for publication October 31, 2006.
Copyright © 2007 by Lippincott Williams & Wilkins, Inc.
From the Trauma Program and the Departments of Surgery (H.C.T.,
L.N.T., S.B.R., J.G., F.S., F.D.B.), Critical Care Medicine (L.N.T., S.B.R.,
F.D.B.), and Medical Imaging (C.C.), Sunnybrook Health Sciences Centre,
University of Toronto; and Canadian Forces Health Services Group, Department of National Defence (H.C.T.), Toronto, Ontario, Canada.
Supported by a grant from Physicians’ Services Incorporated Foundation.
Presented at the Annual Scientific Meeting of the Trauma Association
of Canada, March 22–24, 2006, Banff, Alberta, Canada.
Address for reprints: Homer Tien, MD, FRCSC, Major, Canadian
Forces Health Services Group, Sunnybrook Health Sciences Centre, 2075
Bayview Avenue, Suite H186, Toronto, Ontario, Canada M4N 3M5; email:
homer.tien@sunnybrook.ca.
DOI: 10.1097/TA.0b013e31802d9700
Volume 62 • Number 1
We prospectively measured radiation doses to trauma
patients during their stay in hospital to quantify the biological
risks associated with multiple imaging tests.
PATIENTS AND METHODS
A prospective study was undertaken of all trauma patients assessed at Sunnybrook Health Sciences Centre (a
Level I adult trauma center in Toronto, Canada) from June 1,
2004 to March 31, 2005. All patients arriving direct from the
scene of injury were included. Patients who died during
hospitalization were excluded.
Patients were treated as per Advanced Trauma Life
protocol.7 After primary survey, three optically stimulated
luminescence (OSL) dosimeters (Landauer type K) were
taped to the neck, chest, and groin of each patient. Dosimeters
were removed at discharge or upon request. Control dosimeters were maintained in the trauma room. After removal,
dosimeters were sent to the vendor (Landauer, Glenwood, IL)
for dose determination.
Definitions
Deterministic effect:8 Any biological effect observable
shortly after receiving a radiation dose. Examples are skin
erythema or hematologic suppression. Deterministic effects
require a dose that exceeds a threshold.
Stochastic effects:8 These include long-term cancer induction and genetic effects. A stochastic model assumes a
linear relationship between dose and biological effect. As
such, there is no definitive threshold that is clearly safe.
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The Journal of TRAUMA威 Injury, Infection, and Critical Care
Absorbed dose:9 The quantity (milligray [mGy]) of
energy absorbed from an X-ray beam by any given tissue.
Surface dose is the absorbed skin dose. Organ doses reflect
the absorbed radiation dose of a specified organ.
Dose equivalent:9 The product of the absorbed dose and
a corresponding quality factor for the radiation (millisieverts
[mSv]). The quality factor standardizes the effects of different sources of radiation. For medical X-ray studies, the quality factor is 1. Therefore, absorbed dose and dose equivalent
are identical (mGy ⫽ mSv) for medical X-ray studies.
Effective dose:9 The sum of the dose equivalents (mSv)
for each organ in the body, weighted by a factor to reflect
radiosensitivity. Effective dose estimates the whole-body
dose required to produce the same stochastic risk as the
partial-body dose that was actually delivered by a radiologic
examination. As such, it is the preferred method for quantifying overall risk from diagnostic imaging.
OSL-Based Estimates of Radiation Dose
The OSL dosimeters measured dose equivalent at the
skin surface (surface dose). Organ doses (thyroid, red bone
marrow, and breast) and total effective dose were then calculated from surface doses using the computer package CTDosimetry.xls (ImPACT CT Patient Dosimetry Calculator
version 0.99w; Imaging Performance Assessment of CT
Scanners; St. George’s Hospital, Tooting, London, UK). Total effective dose was only calculated for patients who had
dosimetry results from all three dosimeters. Also, the assumption was made that all radiation measured by the OSLs was
from CT scanning. This assumption was made based on a
calculation of the relative impact of planar and CT procedures
on total patient effective dose. For the trauma population, we
estimated that 90% of the effective dose was a result of CT
scans.
Demographics, injury data, length of stay, intensive care
unit (ICU) stay, operative procedures, imaging examinations,
and outcomes were collected. During the study period, CT
scanning was done using a GE LightSpeed Plus four-slice
scanner (GE Healthcare, Piscataway, NJ). One major change
in our institutional CT protocol involved the installation of
the GE lightspeed dose optimization feature, approximately 6
weeks into the study. This feature was designed to reduce the
radiation dose from CT scans.
Counting Radiologic Procedures: An Independent
Estimate of Radiation Dose
Organ and total effective doses were also estimated by
counting radiologic examinations and then multiplying by
standard effective doses, as reported in the literature.10,11
These dose estimates were then compared with our OSLbased results.
Cancer Risk
Using the OSL-derived effective doses, excess mortality
from leukemia, thyroid, and breast cancer (women) was calculated using the National Council on Radiation Protection
and Measurement (NCRP) Report 115 risk model,12 appropriate for patients ages 20 to 65. Also, excess mortality from
all cancers was calculated using the same model.
This study was performed in compliance with institutional regulations for clinical research. Approval for delayed
consent was obtained. Data are presented as means ⫾ 95%
confidence intervals. All p values are two-tailed and p was set
at 0.05. All analysis was done using SAS software (version
8.02, SAS Institute Inc., Cary, NC).
RESULTS
During the study period, 291 (65.7%) patients were enrolled out of 443 eligible patients. Thirty-two patients died
(11%), leaving 259 study patients who survived to discharge.
In all, 87 patients lost all dosimeters or withdrew, leaving 172
patients who had dosimetry results.
Baseline characteristics are presented in Table 1. Study
patients appeared to have a higher injury severity score and
longer length of stay than nonstudy patients. Likewise, study
patients received more CT scans and planar radiographs than
nonstudy patients (Table 2). Study patients received a mean
of 4.9 (4.5–5.4) CT scans and 13.7 (11.4 –15.9) plain film
examinations during their admission. In all, 86% of the esti-
Table 1 Baseline Characteristics
Study Patients
With Dosimetry
Results
n
Sex
Men (%)
Women (%)
Age
Injury Severity Scale score
Length of stay (days)
ICU length of stay (days)
Mechanism of injury (% blunt trauma)
172
74.0
26.0
39.9 (37.3–42.5)
22.7 (20.7–24.6)
14.9 (12.3–17.6)
3.7 (2.2–5.3)
89.1
Study Patients
With Lost
Dosimeters
87
73.3
26.3
33.7 (30.4–37.0)
14.7 (12.3–17.2)
8.6 (5.6–11.6)
0.6 (0.2–1.1)
69.7
Not Enrolled in
Study
133
73.0
27.0
36.4 (33.6–39.1)
17.2 (15.1–19.4)
11.9 (9.1–14.6)
0.5 (0.2–0.9)
77.6
Data are means (95% confidence interval) unless noted.
152
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Medical Radiation Exposure and Trauma Patients
Table 2 Number and Types of Imaging Tests Obtained During Admission
n
CT scans
Plain film radiography
Interventional radiography
Fluoroscopy
Nuclear medicine scans
Study Patients
With Dosimetry
Results
Study Patients
With Lost
Dosimeters
Not Enrolled in
Study
172
4.9 (4.5–5.4)
13.7 (11.4–15.9)
0.1 (0.04–0.2)
0.3 (0.2–0.4)
0.01 (0–0.02)
87
2.8 (2.3–3.2)
7.3 (5.7–8.8)
0.06 (0.005–0.1)
0.1 (0.05–0.2)
0
133
4.1 (3.6–4.6)
10.9 (9.2–12.6)
0.05 (0.008–0.1)
0.3 (0.2–0.35)
0.03 (0–0.07)
Data are means (95% confidence interval) unless noted.
mated effective radiation dose was from CT scanning in this
study, which was close to our initial estimate of 90%.
In terms of surface doses, most patients received between
0 and 99 mSv of radiation exposure to their torso (chest and
groin). Very few had chest or groin surface doses that exceeded 100 mSv (Fig. 1). Total effective dose for patients
with three dosimeters was 22.7 (17.1 to 28.3) mSv (Table 3).
Study patients, however, had significant neck surface
doses. As a result, thyroid doses were also high. Mean thyroid
dose was 58.5 (48.7– 68.4) mSv (Table 3). In all, 22% (n ⫽
42) had high thyroid doses (over 100 mSv), with a mean of
156.3 mSv (139.8 –172.8).
OSL-based estimates of radiation doses were higher than
estimates obtained from counting radiologic procedures. This
difference was statistically significant with regards to total
effective dose and thyroid dose, and showed a strong trend
for marrow dose. There were no differences between the
estimates for breast doses (Table 3).
Using our OSL-based results, we estimate that 190 excess cancer deaths would arise in 100,000 similarly irradiated
trauma patients. Excess cancer fatality rates for specific organs are reported in Table 4. Of note, 4.4 per 100,000 excess
thyroid cancer deaths would be expected and 11.7 per
100,000 expected in the high exposure subgroup.
Because of nonuniform recruitment of study patients, we
were not able to compare radiation exposures of patients
before and after our institution received the dose optimization
package for its CT scanners. Because of a slow startup to the
study, we only recruited six study patients before the upgrade
was received, and their radiation exposures varied widely.
DISCUSSION
Rapid diagnosis and prioritized treatment of injuries are
the cornerstone of trauma management.8 CT scanning has
become the screening test of choice for most injuries.13–17
Unfortunately, CT examinations result in significantly higher
radiation doses than plain radiography.18
In general, the risk of missing life-threatening injuries
outweighs the small long-term risk for cancer from imaging
tests. However, there is a growing recognition that this small
individual risk for cancer becomes a greater public health
issue when considered in the context of the large number of
examinations performed.19 Furthermore, this risk is accentuated in trauma patients who often receive multiple tests, and
who tend to be more radiosensitive because of their relatively
younger age.20
Two groups have quantified radiation doses to trauma
patients. Kim et al. retrospectively calculated radiation doses
to critically injured patients requiring prolonged ICU stay3
and to pediatric trauma patients.21 They estimated effective
Table 4 Excess Lifetime Cancer Mortality
Excess Cancer
Deaths per 100,000 People
All cancers (age 20–64)
Thyroid cancer
Breast cancer (women only)
Leukemia
Fig. 1. Surface dose by anatomic location.
190
4.4
41.4
13.3
Table 3 Predicted Exposure Versus Measured Dosimetry
Total effective dose
Thyroid (all)
Red marrow (all)
Breast (women)
n
Predicted Exposure (mSv)
Dosimetry Results (mSv)
Paired t Test
108
172
108
40
17.8 (14.5–20.9)
48.0 (44.6–51.5)
17.6 (15.8–19.4)
15.3 (11.6–19.0)
22.7 (17.1–28.3)
58.5 (48.7–68.4)
18.5 (14.5–22.5)
20.9 (7.1–34.7)
0.02
0.03
0.097
0.33
Data are means (95% confidence interval) unless noted.
Volume 62 • Number 1
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The Journal of TRAUMA威 Injury, Infection, and Critical Care
dose by counting the specific studies obtained for each patient
and then multiplying by the typical effective dose reported for
each study. Fitzgerald et al. prospectively measured the exposures of 31 trauma patients by placing dosimeters on them
before X-ray examination.22 However, the dosimeters were
removed after just 24 hours. Also, this study was conducted
between 1980 and 1982, before CT scanning was widely
available, thus limiting its applicability to modern trauma
practice.
We prospectively measured the radiation doses from
diagnostic imaging to trauma patients seen at our institution
using dosimeters. We found that patients were exposed to
significant radiation doses from radiologic examinations.
However, we found that previous studies may have underestimated radiation exposures. These studies estimated effective dose by counting radiologic procedures; in our study, this
method underestimated effective doses when compared with
dosimeter-based results.
Using our dosimeter results, trauma patients received a
mean effective dose of 22.7 mSv. To put this dose in perspective, the average annual background radiation dose to
human beings is approximately 2.4 mSv,23 and the International Commission on Radiation Protection restricts the annual occupational dose limit to the public to 1 mSv.24 The
expected excess cancer mortality expected from this exposure
of 22.7 mSv was 190 per 100,000. Approximately 2.6 million
injured patients are admitted to hospital annually in the
United States.4 Even though the trauma patients in this study
likely represented a more severely injured cohort than the
average injury patient requiring hospital admission, this data
underscores the potential magnitude of this public health
issue.
The radiation exposure was not evenly distributed, but
was higher in the neck compared with the chest or groin. The
mean thyroid dose was 58.5 mSv. However, 22% of these
patients had thyroid doses of 100 mSv or more, with a mean
of 156.3 mSv. The risk for thyroid cancer is significantly
increased after the 100 mSv dose threshold,25 and above this
dose, there is a linear relationship between the dose and the
risk of carcinoma.26 In our study patients, the excess mortality from thyroid cancer was 4.4 per 100,000 patients. Among
patients with thyroid doses greater than 100 mSv, the excess
thyroid cancer mortality was 11.7 per 100,000 persons. Thyroid cancer is rarely fatal, however.27 The number of excess
thyroid cancers expected would be 10-fold higher (i.e., 44
and 117 per 100,000 persons, respectively) for our study
patients.12
As discussed previously, counting radiologic examinations significantly underestimated total effective dose by
approximately 25%, when compared with dosimeter-based
results. One explanation is that technique factors for plainfilm radiographs and CT scans were left to the discretion of
the technician. Variations in technique can result in substantial variations in radiation exposure.28 Also, completing one
satisfactory CT examination sometimes required multiple
154
scans and radiation exposures, which was not always documented in the radiologic record. For example, agitated trauma
patients often move during scanning, compromising the image quality. As a result, repeat scanning often was required to
complete one satisfactory examination. Also, scanning was
sometimes required through different phases of contrast
circulation.29 The total dose delivered by CT for a multiplephase study is the total effective radiation dose per study
multiplied by the number of phases.2
Diagnostic imaging remains a critical part of the evaluation and management of trauma patients. Indeed, any excess
cancer risk from diagnostic imaging should be placed in
perspective; the background lifetime probability of a U.S.
man dying from any cancer during his lifetime is 23%; for a
woman, this probability is 20%.30 Therefore, the excess cancer mortality reported in this study is small compared with a
person’s lifetime risk of developing cancer. As discussed
previously, this small risk is probably outweighed by the risk
of missing injuries. Missed injuries are a major source of
preventable morbidity and mortality in trauma patients31,32
and CT scanning has been shown to reduce the incidence of
missed injuries.33,34
Even so, clinicians should attempt to minimize radiation
dose. One approach would be judicious use of CT scanning.
There is some evidence that CT use could be reduced without
affecting patient outcomes. Rizzo and coworkers reviewed
the use of CT in 1,609 trauma patients. These patients received 2,047 scans. Overall, they concluded that the CT
results only helped in the management of 29% of these
patients.35
Another approach is to work in collaboration with radiologists to optimize CT scanning parameters to reduce dosage
without affecting image quality and to improve shielding
practices. Reducing tube current, for example, is the most
practical way of decreasing CT radiation dose. Other methods
include increasing acceptable image noise and increasing
image slice profile. Kaira et al. reported that abdominal CT
scan quality was acceptable, even with a 50% reduction in
radiation dosage.36 Kalra et al. present a detailed review of
strategies for CT radiation dose optimization and shielding
practices,37 which is beyond the purview of this study. As
discussed previously in our study, the implementation of the
dose-optimization feature occurred early in the study period,
such that we were unable to determine whether it had any
significant effect on overall radiation exposure.
The disproportionate exposure to the neck region of
trauma patients also has implications on medical practice in
nontrauma-related specialties. For example, the standard first
step after history and physical examination for managing
asymptomatic thyroid nodules is a fine-needle aspirate.38 The
exception to this protocol occurs when there is a history of
previous head and neck irradiation; in these cases, thyroidectomy is the immediate next step.39 Although no exposure
thresholds are given to assist in this decision-making process,
standard surgical texts suggest that a childhood history of
January 2007
Medical Radiation Exposure and Trauma Patients
irradiation for tinea capitis would warrant immediate surgery
for a thyroid nodule.40 Modan reported that the average
thyroid dose for tinea capitis treatment was less than 90
mSv.41 In 22% of our study patients, the average measured
thyroid exposure was over 150 mSv. One implication, therefore, is that patients with thyroid nodules should also be
screened for previous trauma, particularly if injury occurred
during childhood, to determine the next appropriate step in
management.
Study Limitations
The major limitation of this study was that it was conducted at an adult trauma center. Radiation exposure is a
greater health issue for children, who are more radiosensitive
and have more years to express stochastic effects. However,
there is some evidence to suggest that our findings are applicable to children. When we counted radiologic procedures to
estimate effective doses, we found that our adult trauma
patients received similar doses as compared with Kim’s pediatric trauma patients (17.8 mSv versus 14.9 mSv).21 As our
dosimeter-based results were significantly higher than these
estimates, we think prospective dosimeter studies are warranted in the pediatric trauma population.
Our cancer risk model also has significant limitations.
Most cancer risk models assume instantaneous exposure.
Fractionated doses of radiation attenuate the stochastic risk,
by allowing time for irradiated tissue to repair radiationinduced damage.20 As a result, the cancer risk is likely overestimated for our study patients because radiation exposure
occurred during their entire stay in hospital.
Another limitation is that we based our cancer-risk estimation on a linear, no-threshold model that was primarily
designed to determine occupational radiation risk.12 The basic philosophy of occupational radiation protection is that any
radiation exposure is potentially bad, because there is no
benefit to the irradiated worker. Thus, this model tends to
overestimate the radiation risk. In considering radiation risk
to patients, however, overestimating risk may be detrimental
because there may be some diagnostic benefit from increasing radiation exposure. For example, the diagnostic quality of
the radiologic examination may be improved by increasing
radiation exposure, thereby reducing the frequency of missed
injuries.
However, our study may also have underestimated the
actual radiation exposure. We excluded referred trauma patients to have the OSL dosimeters in place for all imaging
examinations. A significant proportion of our trauma population is referred from other centers, where they received
multiple CT examinations. Also, many patients required significant numbers of radiologic tests as outpatients after discharge. This radiation exposure also was not captured by our
study.
One last limitation was the enrollment of study patients.
Study patients were significantly sicker (higher Injury Severity Scale score [ISS]) than nonstudy patients and received
Volume 62 • Number 1
more diagnostic imaging. However, our study patients were
still much more representative of the typical trauma patient,
compared with Kim’s study in ICU patients (mean ISS ⫽
32.0).3 Furthermore, our study is unique in that it compared
effective radiation dose estimated by counting procedures
with that obtained using dosimetry results.
CONCLUSION
Trauma patients are exposed to significant amounts of
radiation from diagnostic imaging. This exposure is associated with a small but measurable future excess cancer risk.
Because of the pattern of exposure, thyroid cancer is likely to
be the most important public health issue from this exposure.
Unnecessary CT examinations should be avoided if the results will not affect treatment. Consideration should be given
to implementing dose-reduction protocols and routine shielding practice.
ACKNOWLEDGMENTS
This study was supported by a grant from the Physicians’ Services
Incorporated Foundation. We would also like to acknowledge the support of
the Department of Health Policy, Management and Evaluation at the University of Toronto, and the Department of Surgery at the University of Toronto.
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