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17RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1
......................................................................................................
A
s the number of computed tomography
(CT) procedures performed in the United
States continues to increase, there is grow-
ing concern about patient protection issues.
Currently, no system is in place to track a
patient’s lifetime cumulative dose from medical sources,
and questions have arisen regarding the possible threat to
public health from the widespread use of CT, especially in
pediatric patients.
The authors reviewed the published literature to
determine whether patients are receiving a higher
absorbed dose of radiation and explored several pro-
posed models to optimize the radiation dose delivered
to patients and track cumulative lifetime dose. The
literature review was performed using various key schol-
arly databases and search engines. In an effort to limit
the search to the most recent literature, only articles
that were peer reviewed and published from 2000 to
2006 were selected for review. References to secondary
sources were avoided whenever possible. For compari-
son purposes and to estimate the relative risk increase
for stochastic effects such as cancer, patient doses are
reported as “effective doses,” which are measured in
sieverts (Sv) in the International System of Units. Table
1 summarizes the key findings of this review.
Trends in Patient Dose
Physicians have come to rely on sophisticated imag-
ing techniques to render more accurate diagnoses,1
and CT has become the first-choice modality for many
diagnosticians.2
Scan times have been reduced, result-
ing in increased patient throughput and enhanced
image quality.
A recent study by Aldrich and Williams1
quantified
changes in numbers of radiology exams at Vancouver
General Hospital from 1991 to 2002 and examined
the correlation to the radiation dose received by the
patient. In addition to a 4-fold increase in CT exams,
they also found that the average annual effective dose
per patient almost doubled during the study period,
from 3.3 mSv in 1991 to 6.0 mSv in 2002.1
Other studies
have described the average axial scanning effective dose
for various regions of the body as 6.2 mSv.3
Aldrich and
Williams concluded that CT is the largest contributor to
patient dose in radiology. This could be because more
CT scanners are in use and their performance has been
enhanced, along with increasing indications for CT
exams.1
In 2003 it was estimated that up to 29% of all
CT units in the United States were capable of perform-
ing multidetector spiral scans, and it is likely that this
number is much higher now.3
Patient Dose From CT:
A Literature Review
John E. Colang, M.S.R.S., R.T.(R), PMP
Jeff B. Killion, Ph.D., R.T.(R)(QM)
Eliseo Vano, Ph.D.
Context  Computed tomography (CT) exams are increasingly common and account for a significant portion of individuals’ mounting
exposure to medical radiation.
Objective  To explore issues surrounding patient radiation dose, including techniques for minimizing dose and the feasibility of track-
ing lifetime exposure to medical radiation from CT and other imaging exams.
Methods  The authors conducted a review of the recent literature to assess current knowledge of dose levels, protocols for minimizing
patient dose and possible systems for tracking cumulative dose.
Results  Currently, no regulations are in place to track cumulative patient radiation dose. However, the authors discuss possible
means of recording, tracking and storing this data, such as standardizing its inclusion in DICOM headers and transmitting it to elec-
tronic personal health records.
Conclusion  More research is needed to develop and implement uniform dose tracking procedures and protocols for minimizing patient dose.
.............................................................................................................
PATIENT DOSE FROM CT
18 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY
CT is not the only modality that has experienced
more use and has the potential to deliver higher patient
radiation doses. Vano and Gonzalez studied radiation
injuries from interventional fluoroscopic procedures.4
Their study outlined possible root causes of radiation
injuries from fluoroscopic procedures, including misuse,
system faults and nonoptimized operational protocols. It
drew attention to the fact that optimizing technique and
standardizing practice could benefit the field of radiology
and protect patients from overexposure to ionizing radia-
tion. Although not pivotal to the discussion of correlating
increased use of CT to an increased patient radiation
dose, Vano and Gonzalez’s study calls attention to the fact
that dose to the patient
can be reduced by care-
ful attention to technique
and optimization.
Yoshizumi and Nelson
pointed out the need to
balance optimization of
image quality against
radiation dose in devel-
oping clinical protocols.3
Their study described
fundamental concepts of
radiation dose in detail,
including the CT dose
index and other techni-
cal factors such as pitch
effect, dose profile in the
penumbra and signal-to-
noise ratio. Yoshizumi
and Nelson concluded
that multidetector CT
(MDCT) radiation
dosimetry issues have
not been addressed ade-
quately and have lagged
behind advances in the
actual technology.3
Other researchers also
are questioning the effect
of newer imaging tech-
nologies on patient radia-
tion dose. Berland and
Smith proposed that the
absorbed dose could be
up to 40% higher using
MDCT compared with
older generation scan-
ners.5
Golding and Shrimpton suggested that “evidence
indicates a strong trend of increasing population dose
owing to rising use of CT and to increased dose per
examination.”6
A significant body of literature focuses
on discovering a causal link between increased use of
the CT scanner and an increase in radiation absorbed
dose to the patient population.
Numerous studies have suggested that, although CT
is not the most commonly performed radiologic exami-
nation, it is the largest source of radiation dose. Nagel
et al found that, although CT represents only about 4%
of all radiologic examinations, it is responsible for up to
35% of the collective radiation dose to the population
Table 1
Summary of Literature Review
Technical Factors:
Radiology departments should:
  ■ Focus on scanner protocols to reduce pediatric CT dose (mAs).
  ■ Use CT scanners with automatic exposure settings to limit dose.
  ■ Limit the region scanned to a minimum.
  ■ Adopt diagnostic reference levels.
  ■ Implement child-size guidelines.
  ■ Develop guidelines to compare dose indicators with standards.
  ■ Ensure that the indicator of CT dose (CTDIvol) is visible on the display console.
  ■ Include a DICOM file-format tag for CT dose information.
Educational Issues:
Imaging professionals should educate themselves on how to optimize exposure settings.
Patients should be informed of the risks of ionizing radiation from medical sources, but this
should be balanced with an explanation of how benefits from CT scanning and other medi-
cal sources often outweigh risks.
Health care professionals must be prepared to discuss with parents why CT is sometimes
the best exam to diagnose conditions in children.
Ordering physicians should be educated to request only necessary CT exams.
Emerging Trends:
Guidelines and standards are evolving that may lead to regulations for monitoring lifetime
cumulative radiation dose from medical imaging sources.
More attention will be focused on cancer risks for pediatric patients undergoing multiple
CT scans.
Additional support will go to CT research and clinical studies.
New government regulations are possible, with Europe leading the way.
ALARA (as low as reasonably achievable) will continue to be the goal.
.............................................................................................................
19RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1
COLANG, KILLION, VANO
from radiologic examinations.7
In a related National
Cancer Institute report, data suggested that the use of
CT in adults and children has increased approximately 7
fold in the past 10 years.2
In large U.S. hospitals, CT rep-
resents 10% of diagnostic procedures and accounts for
approximately 65% of the effective radiation dose for all
medical examinations.2
Aldrich et al conducted a study to compare the dose
length product and effective radiation dose to patients
from CT examinations in British Columbia, Canada.8
They compared data from 1070 CT exams and conclud-
ed that considerable variation existed in the dose length
product and patient radiation dose for a specific exam.
This study called attention to the need to optimize
the effective dose to the patient and to conduct more
research to determine which additional efforts are need-
ed to minimize patient exposure. Optimizing technical
factors for exams can help reduce the patient radiation
dose, thereby reducing risks.9,10
A pivotal study by Lee et al assessed awareness levels
among patients, emergency department physicians and
radiologists concerning radiation dose and the risks
involved with CT scans.9
Lee and colleagues concluded
that patients were not given information about the risks,
benefits and radiation dose for a CT scan.9
Regardless
of their experience levels, few of the participants in the
study (including the emergency department physicians
and the radiologists) were able to provide accurate
estimates of CT radiation doses. This study underscores
the prevalent lack of attention to the issue of lifetime
cumulative radiation dose. This must become a central
issue so that risk can be studied and monitored. One
disadvantage to communicating the risk of a cumulative
radiation dose would be the natural instinct of some
patients to defer or cancel the exam.9
Professionals
should highlight the benefits of the examination when
discussing risks with the patient. Table 2 presents a list
of questions and answers intended to help referring phy-
sicians improve their understanding of radiation risks
from medical imaging exams.
CT Dose and Pediatric Patients
CT remains a very important modality for diagnos-
ing disorders in pediatric patients. However, children
are at a greater risk because they have a longer lifetime
to manifest a radiation-related cancer. Frush et al drew
interesting corollaries between the widespread use of
x-rays in the early days of radiography, before the damag-
ing effects of radiation were understood fully, and today’s
widespread use of CT on pediatric patients.11
Frush and
colleagues explored the risks of low-level radiation and
CT11
and advocated following the ALARA principle (as
low as reasonably achievable). Their research suggested
a statistically significant, increased risk of fatal cancer
from low-dose radiation in the range of 50 to 100 mSv.
“For example,” they wrote, “a single CT of the abdomen
could provide a dose of 11 mSv. If there are 3 phases in
this examination, the actual dose is 33 mSv (3 x 11 mSv).
If this child is 1 of the 30% who have 3 or more examina-
tions, the lifetime dose is at least 100 mSv, clearly in the
range of doses associated with induction of fatal cancer.”11
Table 3 lists some common pediatric CT exams and asso-
ciated radiation doses.
Donnelly also drew parallels between the early
decades of radiography and contemporary use of CT.12
The author pointed out the increasing use and potential
misuse of examinations, the lack of attention to dose
risks, particularly in children, and the delay in imple-
menting dose reduction strategies, all of which combine
to form an interesting parallel to the early days of radiol-
ogy. One fact emerges clearly throughout the body of
knowledge in radiology: Attention must be drawn to the
ALARA principle, especially where pediatric patients
and CT are concerned.2,11
The National Cancer Institute suggested several
steps to reduce the radiation dose to children.2
First,
only necessary CT examinations should be performed.
Pediatricians and radiologists should consult to deter-
mine whether CT is the most appropriate examination.
Second, if CT is the appropriate modality, exposure
parameters should be adjusted to optimize the study
and minimize the dose to the patient. Specifically, radio-
logic technologists should:
n	 Limit the region scanned to the smallest
possible area.
n 	Optimize the mA settings for the organ systems to
be examined (eg, lower mA for skeletal and lung
exams).
n 	Adjust technique to the child’s size and weight.
n 	Determine appropriate scan resolution (eg, a
lower resolution may be sufficient for some diag-
nostic purposes).2
Physicians should minimize the use of multiple scans
for contrast enhancement. Finally, radiology depart-
ments should develop pediatric CT protocols that
describe these steps.
McLean also emphasized the importance of adjusting
pediatric radiographic settings during CT to minimize
dose.13
McLean summarized optimization methods and
suggested that further clinical studies be conducted on
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PATIENT DOSE FROM CT
20 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY
pediatric CT dose. Despite the overwhelming public
health benefits of CT, McLean suggested implementing
the following steps to protect an increasing population
of children from cancer risks related to CT:
n 	Focus on scanner protocols to reduce pediatric
CT dose (mAs).
n 	Use CT scanners with automatic exposure settings
to limit dose.
n 	Develop guidelines to compare dose indicators
with standards.
Table 2
Questions and Answers To Help Physicians Understand Radiation Risks From CT
Why is an x-ray procedure, such as a CT
examination, hazardous?
X-rays are high energy, ionizing radiation and will break apart DNA
molecules. Light sources and microwaves have much lower energies,
which are insufficient to break up molecules.
What are the hazards of x-rays? The major concern from x-ray exposure is induction of cancer.
Is there a safe level of x-ray exposure? There is no radiation exposure level below which the risk is zero. In
general, the radiation risks are directly proportional to the amount of
radiation absorbed by the patient.
How long does it take for a radiation-induced
cancer to be expressed?
Radiation-induced leukemias have a latent period of a few years, where-
as it takes decades for radiation-induced solid tumors to manifest.
Do radiation-induced cancers differ from
naturally occurring cancers?
No, radiation-induced cancers can be detected only by epidemiologi-
cal studies that compare an exposed group with a corresponding con-
trol group.
How does a chest CT examination compare
with a chest x-ray examination?
The patient dose from a typical chest CT examination (5 to 10 mSv) is
more than 100 times larger than a conventional chest x-ray examina-
tion (0.05 mSv).
How does a chest CT examination compare
with natural, background radiation?
CT examination exposures generally are higher than 1 year’s worth of
background radiation exposure (~3 mSv).
What is the cancer risk for a patient under-
going a typical CT examination?
A CT scan with a dose of 10 mSv has an average cancer induction
risk of about 1 in 1000, with half of those cancers being fatal (most are
expressed decades after the scan).
Does the age of the patient at time of
exposure affect the patient risk?
Definitely! Risks to children are about 3 times higher than those for a
young adult. Risks to someone aged 50 years will be about 3 times
lower than average.
Have CT examinations been shown to cause
cancer?
No, as the overall cancer incidence is approximately 420 in a popula-
tion of 1000; detecting a small excess (ie, 1 per 1000) would be dif-
ficult in an epidemiological study.
What factors should I consider prior to
ordering a CT examination on a patient?
It is essential to balance the radiation risks with the corresponding
patient benefits.
What are the general guidelines and policies
for performing CT scans?
Eliminate unnecessary (nonindicated) examinations and ensure that
no more radiation than is needed is used to perform an examination.
When is a CT scan indicated? Patient benefits should be greater than the risks. Radiologists can
advise on the risks and benefits of CT scans, as well as the use of
nonionizing imaging methods.
How can patient radiation levels be kept as
low as reasonably achievable (ALARA)?
Radiological studies should be tailored to specific clinical needs. For
example, a chest CT exam to assess lung disease in a child with cys-
tic fibrosis would need (much) less radiation.
Courtesy of Dr Walter Huda, Department of Radiology, Medical University of South Carolina, Charleston.
.............................................................................................................
21RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1
COLANG, KILLION, VANO
n 	Ensure that the
indicator of CT
dose (CTDIvol) is
visible on the dis-
play console.
n 	Include a
DICOM (Digital
Imaging and
Communications
in Medicine) file-
format tag for CT
dose information.
n 	Emphasize educa-
tion regarding CT
protocols and dose
implications.
The Profession’s
Position on
Controlling Dose
Consensus in the
literature reveals mount-
ing concern regarding
radiation dose in CT.
This is reflected in inter-
national efforts to raise awareness about this issue. One
group of scientists observed at a U.S. Food and Drug
Administration science forum: “Our situation is given
new impetus by new European and national regulations
that require departments to introduce robust proce-
dures for the protection of the patient, including the
twin elements of ensuring clinical justification of the
examination and optimization of the technique.”14
In the United States, current practice does not
include tracking the cumulative lifetime dose of ion-
izing radiation from medical imaging devices, nor are
patients regularly informed of the risks of increased
exposure to radiation from medical devices. However,
this practice is beginning to shift in Europe, as evi-
denced by the European Council Directive that outlines
steps to ensure that patients and practitioners are edu-
cated about the risks involved with radiation exposure,
as well as steps to minimize the radiation dose to the
patient.14
The directive, 97/43/euratom, stopped short
of mandating a record of the actual patient dose, not-
ing that “Medical exposure continues to constitute the
major source of European Union citizens’ exposure to
artificial sources of ionizing radiation. However, the use
of ionizing radiation has allowed great progress in many
areas of medicine. It is therefore essential that practices
involving medical exposure are carried out in optimized
radiation protection conditions.”14
Similar efforts are underway in the United States to
optimize procedures and thereby minimize radiation
dose to the patient. Stern et al cited 9 proposed changes
to the U.S. Performance Standard for Diagnostic X-Ray
Equipment that will reduce unnecessary radiation emit-
ted during fluoroscopy.10
These are steps in the right
direction but, like the European Council directive, fall
short of fully regulating the measurement of patient
radiation dose. A search of the literature did not reveal
consensus among researchers regarding how these steps
could be implemented in widespread practice.
The literature also underscores the need to develop
and adopt reference dose standards for CT examina-
tions. For example, Mayo et al found that large varia-
tions exist in technical factors used in pediatric chest
CT.15
They encouraged radiology departments to
adopt reference dose value standards for these exams.
Adopting these standards could benefit all patients
undergoing CT exams.
The Role of Information Technology
Lacking in the literature is any mention of how the
medical imaging community will implement a cradle-to-
Table 3
Approximate Radiation Dose by Pediatric Exam Type and Organ
Exam Type Relevant Organ Approximate
Equivalent Dose to
Relevant Organ (mSv)
Pediatric head CT scan
unadjusted settingsa
(200 mAs, neonate)
Brain 60
Pediatric head CT scan
adjusted settingsb
(100 mAs, neonate)
Brain 30
Pediatric abdominal CT scan
unadjusted settings
(200 mAs, neonate)
Stomach 25
Pediatric abdominal CT scan
adjusted settings
(50 mAs, neonate)
Stomach 6
Chest x-ray (PA/lateral) Lung 0.01 / 0.15
Screening mammogram Breast 3
a
“Unadjusted” refers to using the same settings as for adults.
b
“Adjusted” refers to settings adjusted for body weight.
.............................................................................................................
PATIENT DOSE FROM CT
22 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY
grave radiation dose monitoring system. As discussion
about tracking lifetime radiation dose from CT and other
imaging modalities begins, a wide range of policy and
technology changes will have to coalesce to develop the
future model. First, government entities might consider
including radiation dose in patients’ permanent medical
records. Second, radiology personnel, physicians, nurses
and other allied health workers must receive education
and training to understand the importance of good
management of patient doses. Limiting lifetime patient
cumulative dose should be a goal, with the understanding
that occasionally there will be medical reasons to justify
the use of a higher dose. Additional education and train-
ing will be needed to help health care professionals better
inform patients of the risks involved. Finally, a partner-
ship of technologies and standards will have to be formed
to allow the practice to change.
As these changes find their way into the workplace,
it will be necessary to develop a mechanism by which
imaging equipment can transmit patient absorbed
dose data to the radiology information system (RIS)
or the picture archiving and communications system
(PACS). Modern digital radiology equipment produces
images with the dosimetric information contained in
the DICOM header file. Vano et al pointed out that
cooperation between the International Electrotechnical
Commission and the radiology industry regarding stan-
dardization of the DICOM header will enable auditing
of x-ray procedures and patient dose.16
An immediate
benefit of this effort would be automatic records that
would reference comparison dose values and trigger an
alarm if 1 of the monitored parameters was outside of
an acceptable range.16
A review of the literature reveals a gap in how this
information would be transmitted from the imaging
device to a monitoring and archiving system. A pos-
sible model could include the RIS or the PACS trans-
mitting the dose information to the personal health
record, the enterprise health record or a regional
health organization. At this point, the literature does
not indicate which regulatory body would be the ulti-
mate custodian of this data. A future model would
need to describe how dose information from all medi-
cal imaging centers would be routed to a central data
store for a patient. Careful evaluation and planning
would be needed to provide a seamless transport
conduit for these data. Health Insurance Portability
and Accountability Act constraints regarding patient
privacy could prove to be a challenge to implementing
this model. Another possible constraint could be the
cost of implementing a national model and developing
a regulatory board to govern its policies.
One proposed model uses technology within the
imaging device to transmit the dose information in real
time to the PACS via DICOM using the modality-
performed procedure step, or a newly proposed struc-
tured report within DICOM.16
Important work has
been done in this area by Vano et al, who suggested
an online audit of the actual dose by comparing the
dose to a diagnostic reference level.17
“According to the
International Commission on Radiological Protection,
the average patient dose for a specific examination type
should be compared with the diagnostic reference level
for the examination.”16
Vano and colleagues proposed a tool to identify any
abnormal patient dose and determine the cause of the
overexposure.17
Their report describes the benefits and
results derived from this model of online quality control.
The authors proposed generating real-time alarms when
baseline minimum doses were reached. In computed
radiography, the exposure index would be audited. In
interventional radiology, dose area product, number of
images per series, total number of series and total num-
ber of images per procedure also would trigger an alarm
if studies exceeded the baseline parameters. Additional
research is required to determine whether real-time
alarms for excessive doses are effective as an optimiza-
tion technique.
DICOM Component
The DICOM standard was created by the National
Electrical Manufacturers Association to enable trans-
mission and viewing of medical images. DICOM has
become the accepted conduit for transmitting medi-
cal image data throughout the world. Part 10 of the
standard describes a file format for the distribution
of images. Balter et al examined a variety of technical
information describing image acquisition.18
These data
can be found in the DICOM headers of digital images.
The authors described placing key exposure data in
various public data elements and private fields. Because
no standard currently exists, the exact location of this
information depends on the manufacturer. Table 4 dem-
onstrates an example of DICOM tags in the header of a
generic flat panel. According to Balter and colleagues,
efforts are underway to standardize the architecture
for digital fluoroscopy: “A cooperative effort between
the International Electrotechnical Commission and the
DICOM committee is currently defining those dosimet-
ric elements that should be stored for every examination
.............................................................................................................
23RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1
COLANG, KILLION, VANO
performed using ‘digital’
[sic] x-rays and its storage
structure within DICOM
public fields.”18
Downstream Data
Repositories
Currently, there is
no standard for acquir-
ing, evaluating and
archiving digital imaging
data. Until a standard is
implemented, important
research needs to be
done concerning proto-
type practice standards
that permit dissemination
of these data. Equipment
manufacturers will need
to reach consensus on
a standard. Vano et al
found that, at present,
manufacturers of x-ray
systems differ in how they
populate the content of
dosimetric information
in the DICOM header.16
Downstream data reposi-
tories could consist of
RIS, PACS or any other subordinate system that would
receive data from the modality. Dose data from the
DICOM object could be transmitted electronically using
a standardized format to a national data store or to a
patient’s personal health record or enterprise patient
medical record. Figure 1 describes how image acquisi-
tion data could be transmitted to a national database or
to RIS or PACS from the DICOM object.
Future Directions
A plethora of data implicates medical sources as the
public’s number 1 source of exposure to ionizing radia-
tion. “In the 2000 report of the United Nations Scientific
Committee on the Effects of Atomic Radiation, it was
stated that medical applications of ionizing radiation rep-
resented by far the largest man-made source of ionizing
radiation exposure.”19
Despite the fact that the benefits to
the patient are enormous, lifetime cumulative exposure
risks must be addressed. A search of the literature did not
reveal any current requirements in the United States or
Europe to track and monitor lifetime cumulative radiation
dose to patients from medical imaging techniques such
as CT and fluoroscopy. In the absence of requirements, a
call is emerging for additional studies to describe the most
efficient way to address this issue. The literature search
did not reveal any effort to standardize key reporting vari-
ables in the United States, nor did it reveal consensus on
efforts to standardize optimization methods and practices.
One important aspect in understanding dose report-
ing is that recording individual irradiation events is not
sufficient for documentation purposes. Several regula-
tory bodies in different countries have recommended
recording accumulated dose values such as the “dose at
the reference point” or the “dose area product” per pro-
cedure. However, to complete dose reporting require-
ments, a distinct set of accumulated values must be
provided to fulfill legal requirements for “recording of
accumulated values applied during a procedure.”19
Although definitions of diagnostic reference levels
vary, they share common elements that include dose
levels, standard-size patients or phantoms, dose quantity
and specific equipment.20
A recent article by Seeram and
Table 4
Sample Data From DICOM Tags in the Header of a Chest Flat Panel
(0008,0020) Study date 7/01/03
(0008,0030) Study time 10:31:12
(0008,0033) Image time 10:32:43
(0010,0020) Patient ID NNNNNNN
(0010,0040) Patient’s sex F
(0010,1010) Patient’s age 085Y
(0018,0015) Body part examined Chest
(0018,0060) kVp 125
(0018,1150) Exposure time 5
(0018,1151) X-ray tube current 250
(0018,115E) Image area dose product 0.83557
(0018,1190) Focal spot(s) 0.6
(0018,1405) Relative x-ray exposure 61
(0018,7060) Exposure control mode AUTOMATIC
(0018,7062) Exposure control mode description AEC_left_and_right_cells
(0028,0010) Rows 2022
(0028,0011) Columns 2022
(0028,0100) Bits allocated 16
(0028,0101) Bits stored 14
.............................................................................................................
PATIENT DOSE FROM CT
24 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY
Brennan underscored the need for optimization and
use of diagnostic reference levels (DRLs).20
Their article
focused on managing patient dose in diagnostic radiol-
ogy by using DRLs, along with principles for optimizing
radiation protection. DRLs
must be relevant to the locale
where they are applied and
should be determined from
radiation dose survey data.20
The article discussed the 2
triads of radiation protection
— principles (ie, optimiza-
tion, justification and dose
limitation) and actions (ie,
time, distance and shielding).
According to Seeram and
Brennan, DRLs should be
considered a dynamic param-
eter, and hospitals should
perform regular dose surveys
to ensure that levels remain
applicable to new hospital
equipment.20
The authors sug-
gested that a variety of param-
eters be examined when
conducting a dose survey,
including examination type,
the number and type of hos-
pitals involved, phantom and
patient investigations, dosime-
try methods, establishment of
the reference level and acces-
sory information.20
Seeram
and Brennan were careful to
point out that, although opti-
mization of the technique is
an important step in limiting
patient dose, care should be
taken to ensure image quality
remains high.
DRLs are a step in the
right direction to standard-
ize practice. The literature
reveals that attention is
beginning to focus on how
radiology professionals
could communicate and
handle lifetime cumulative
radiation dose from medical
imaging devices. For now,
Europe continues to lead the way in implementing a
standard of practice for monitoring cumulative radia-
tion dose from medical imaging. Supplement 94 of the
DICOM Standards Committee, Working Group 6, Base
DICOM is used to
transmit the dose informa-
tion via the MPPS (modality-
performed procedure step) or
through radiation dose structured
report in DICOM using an indus-
try accepted standard (IEC
and DICOM).
Is a national,
regional or enterprise patient
dose database available?
Does
the patient have
a PHR (personal health
record)?
Patient
cumulative dose
could be added to
radiology informa-
tion system or
PACS. (RIS or
PACS must be
implemented to
accept these
data.)
Patient cumulative
dose is added to
data store using
future standard
messaging
technology.
Cumulative dose
data written in
PHR using an
Extensible Markup
Language
standard such
as XML.
Imaging modality such as
CT or other computerized
radiology system generates
dose information in “real
time” as the patient’s image
is acquired.
Yes
Yes
No
No
END
END
Figure 1. Sample data flow from the CT scanner to a downstream data warehouse or personal health record.
.............................................................................................................
25RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1
COLANG, KILLION, VANO
5.	 Berland LL, Smith JK. Multidetector-array CT: once
again, technology creates new opportunities. Radiology.
1998;209(2):327-329.
6.	 Golding SJ, Shrimpton PC. Radiation dose in CT: are we
meeting the challenge? Br J Radiol. 2002;75(889):1-4.
7.	 Nagel H, Galanski M, Hidajat N, Maier W, Schmidt T.
Radiation exposure in computed tomography: fundamen-
tals, influencing parameters, dose assessment, optimiza-
tion, scanner data, terminology. Paper presented at the
COCIR 2000, Frankfurt, Germany.
8.	 Aldrich JE, Bilawich AM, Mayo JR. Radiation doses to
patients receiving computed tomography examinations in
British Columbia. Can Assoc Radiol J. 2006;57(2):79-85.
9.	 Lee CI, Haims AH, Monico EP, Brink JA, Forman HP.
Diagnostic CT scans: assessment of patient, physician, and
radiologist awareness of radiation dose and possible risks.
Radiology. 2004;231(2):393-398.
10.	 Stern S, Tucker S, Gagne R, Shope T. Estimated benefits
of proposed amendments to the FDA radiation-safety stan-
dard for diagnostic x-ray equipment. Paper presented at the
2001 FDA Science Forum, Washington, DC.
11.	 Frush DP, Donnelly LF, Rosen NS. Computed tomography
and radiation risks: what pediatric health care providers
should know. Pediatrics. 2003;112(4):951-957.
12.	Donnelly LF. Lessons from history. Pediatr Radiol.
2002;32(4):287-292.
13.	McLean D. Computed tomography doses in children.
Lancet. 2004;363(9416):1178.
14.	 Radiological protection for persons undergoing medical
examination or treatment. Europa Web site. www.europa.
eu/scadplus/leg/en/cha/c11546b.htm. Updated August 17,
2006. Accessed July 4, 2006.
15.	Mayo JR, Aldrich J, Muller NL; Fleischner Society.
Radiation exposure at chest CT: a statement of the
Fleischner Society. Radiology. 2003;228:15-21.
16.	Vano E, Padovani R, Neofotistou V, et al. Improving patient
dose management using DICOM header information. The
European SENTINEL experience. itab2006 International
Congress, Greece, 2006.
17.	 Vano E, Fernandez JM, Ten JI, Gonzalez L, Guibelalde E,
Prieto C. Patient dosimetry and image quality in digital
radiology from online audit of the x-ray system. Radiat Prot
Dosimetry. 2005;117(1-3):199-203.
18.	Balter S, Vano E, Gonzalez L. Fluoroscopic patient dosim-
etry from dicom headers. 11th International Congress
of the International Radiation Protection Association.
Madrid, Spain, 2004.
19.	 International Atomic Energy Agency. International action
plan for the radiological protection of patients: report by
the Director General. wwwns.iaea.org/downloads/rw
/radiation-safety/patientprotactionplangov200236gc4612
.pdf. Accessed July 3, 2006.
20.	Seeram E, Brennan PC. Diagnostic reference levels in radi-
ology. Radiol Technol. 2006;77(5):373-384.
Standard, proposes a standard for capturing these data
during image acquisition.21
Conclusion
The use of MDCT is on the rise and accounts for a
large percentage of patient radiation exposure from
medical imaging devices. A growing number of research-
ers in the medical imaging community are calling for
heightened awareness of patient radiation dose from CT
and other medical imaging radiation sources. Efforts are
underway to examine methods and practices to allow the
profession to reduce patient radiation exposure and track
the lifetime cumulative radiation dose. Technical com-
ponents will have to be standardized and implemented
throughout the imaging community. Using DICOM as the
principal transmission agent, a modality-performed
procedure-step object or a newly proposed structured
report template could be used to transmit patient radia-
tion data downstream to a recipient PACS, RIS, personal
health record, enterprise health record or yet-to-be-
defined entity or object. Several technical and procedural
issues remain and are not described fully in the literature.
In addition, further research is needed to deter-
mine the most appropriate method to develop and
implement best practices that minimize exposure to
patients by optimizing technical factors. More research
also is needed on how to evaluate the efficacy of imple-
menting a national radiation dose database to monitor
a patient’s lifetime exposure to ionizing radiation from
medical imaging devices. Radiology professionals, as
well as the general public, should educate themselves
regarding the most effective ways to monitor patient
cumulative radiation dose from CT and other medi-
cal imaging sources. In the interim, the focus should
remain on optimizing image quality while conveying a
minimal radiation dose to the patient.
References
1.	 Aldrich J, Williams J. Change in patient doses from radio-
logical examinations at the Vancouver General Hospital,
1991-2002. Can Assoc Radiol J. 2005;56(2):94-99.
2.	 Radiation risks and pediatric computed tomography (CT):
a guide for health care providers. National Cancer Institute
Web site. www.cancer.gov/cancertopics/causes/radiation-
risks-pediatric-CT. Published August 20, 2002. Accessed
October 6, 2006.
3.	 Yoshizumi TT, Nelson RC. Radiation issues with multidetec-
tor row helical CT. Crit RevComput Tomogr. 2003;44(2):95-117.
4.	 Vano E, Gonzalez L. Avoiding radiation injuries from inter-
ventional fluoroscopic procedures. Eur Radiol Supplements.
2004;14:59-66.
.............................................................................................................
PATIENT DOSE FROM CT
26 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY
21.	 Digital imaging and communications in medicine
(DICOM): supplement 94: diagnostic x-ray radiation
reporting dose special report (2005). Rosslyn, VA: DICOM
Standards Committee.
John E. Colang, M.S.R.S., R.T.(R), PMP, is a project
manager for digital health projects with Intel Corporation in
Albuquerque, New Mexico. Jeff B. Killion, Ph.D., R.T.(R)
(QM), is an associate professor in the department of radiologic
science at Midwestern State University in Wichita Falls, Texas.
Eliseo Vano, Ph.D., is a professor of medical physics in the radi-
ology department at Complutense University in Madrid, Spain.
Reprint requests may be sent to the American Society of
Radiologic Technologists, Communications Department, 15000
Central Ave. SE, Albuquerque, NM 87123-3909.
©2007 by the American Society of Radiologic Technologists.

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  • 1. peer review 17RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1 ...................................................................................................... A s the number of computed tomography (CT) procedures performed in the United States continues to increase, there is grow- ing concern about patient protection issues. Currently, no system is in place to track a patient’s lifetime cumulative dose from medical sources, and questions have arisen regarding the possible threat to public health from the widespread use of CT, especially in pediatric patients. The authors reviewed the published literature to determine whether patients are receiving a higher absorbed dose of radiation and explored several pro- posed models to optimize the radiation dose delivered to patients and track cumulative lifetime dose. The literature review was performed using various key schol- arly databases and search engines. In an effort to limit the search to the most recent literature, only articles that were peer reviewed and published from 2000 to 2006 were selected for review. References to secondary sources were avoided whenever possible. For compari- son purposes and to estimate the relative risk increase for stochastic effects such as cancer, patient doses are reported as “effective doses,” which are measured in sieverts (Sv) in the International System of Units. Table 1 summarizes the key findings of this review. Trends in Patient Dose Physicians have come to rely on sophisticated imag- ing techniques to render more accurate diagnoses,1 and CT has become the first-choice modality for many diagnosticians.2 Scan times have been reduced, result- ing in increased patient throughput and enhanced image quality. A recent study by Aldrich and Williams1 quantified changes in numbers of radiology exams at Vancouver General Hospital from 1991 to 2002 and examined the correlation to the radiation dose received by the patient. In addition to a 4-fold increase in CT exams, they also found that the average annual effective dose per patient almost doubled during the study period, from 3.3 mSv in 1991 to 6.0 mSv in 2002.1 Other studies have described the average axial scanning effective dose for various regions of the body as 6.2 mSv.3 Aldrich and Williams concluded that CT is the largest contributor to patient dose in radiology. This could be because more CT scanners are in use and their performance has been enhanced, along with increasing indications for CT exams.1 In 2003 it was estimated that up to 29% of all CT units in the United States were capable of perform- ing multidetector spiral scans, and it is likely that this number is much higher now.3 Patient Dose From CT: A Literature Review John E. Colang, M.S.R.S., R.T.(R), PMP Jeff B. Killion, Ph.D., R.T.(R)(QM) Eliseo Vano, Ph.D. Context  Computed tomography (CT) exams are increasingly common and account for a significant portion of individuals’ mounting exposure to medical radiation. Objective  To explore issues surrounding patient radiation dose, including techniques for minimizing dose and the feasibility of track- ing lifetime exposure to medical radiation from CT and other imaging exams. Methods  The authors conducted a review of the recent literature to assess current knowledge of dose levels, protocols for minimizing patient dose and possible systems for tracking cumulative dose. Results  Currently, no regulations are in place to track cumulative patient radiation dose. However, the authors discuss possible means of recording, tracking and storing this data, such as standardizing its inclusion in DICOM headers and transmitting it to elec- tronic personal health records. Conclusion  More research is needed to develop and implement uniform dose tracking procedures and protocols for minimizing patient dose.
  • 2. ............................................................................................................. PATIENT DOSE FROM CT 18 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY CT is not the only modality that has experienced more use and has the potential to deliver higher patient radiation doses. Vano and Gonzalez studied radiation injuries from interventional fluoroscopic procedures.4 Their study outlined possible root causes of radiation injuries from fluoroscopic procedures, including misuse, system faults and nonoptimized operational protocols. It drew attention to the fact that optimizing technique and standardizing practice could benefit the field of radiology and protect patients from overexposure to ionizing radia- tion. Although not pivotal to the discussion of correlating increased use of CT to an increased patient radiation dose, Vano and Gonzalez’s study calls attention to the fact that dose to the patient can be reduced by care- ful attention to technique and optimization. Yoshizumi and Nelson pointed out the need to balance optimization of image quality against radiation dose in devel- oping clinical protocols.3 Their study described fundamental concepts of radiation dose in detail, including the CT dose index and other techni- cal factors such as pitch effect, dose profile in the penumbra and signal-to- noise ratio. Yoshizumi and Nelson concluded that multidetector CT (MDCT) radiation dosimetry issues have not been addressed ade- quately and have lagged behind advances in the actual technology.3 Other researchers also are questioning the effect of newer imaging tech- nologies on patient radia- tion dose. Berland and Smith proposed that the absorbed dose could be up to 40% higher using MDCT compared with older generation scan- ners.5 Golding and Shrimpton suggested that “evidence indicates a strong trend of increasing population dose owing to rising use of CT and to increased dose per examination.”6 A significant body of literature focuses on discovering a causal link between increased use of the CT scanner and an increase in radiation absorbed dose to the patient population. Numerous studies have suggested that, although CT is not the most commonly performed radiologic exami- nation, it is the largest source of radiation dose. Nagel et al found that, although CT represents only about 4% of all radiologic examinations, it is responsible for up to 35% of the collective radiation dose to the population Table 1 Summary of Literature Review Technical Factors: Radiology departments should:   ■ Focus on scanner protocols to reduce pediatric CT dose (mAs).   ■ Use CT scanners with automatic exposure settings to limit dose.   ■ Limit the region scanned to a minimum.   ■ Adopt diagnostic reference levels.   ■ Implement child-size guidelines.   ■ Develop guidelines to compare dose indicators with standards.   ■ Ensure that the indicator of CT dose (CTDIvol) is visible on the display console.   ■ Include a DICOM file-format tag for CT dose information. Educational Issues: Imaging professionals should educate themselves on how to optimize exposure settings. Patients should be informed of the risks of ionizing radiation from medical sources, but this should be balanced with an explanation of how benefits from CT scanning and other medi- cal sources often outweigh risks. Health care professionals must be prepared to discuss with parents why CT is sometimes the best exam to diagnose conditions in children. Ordering physicians should be educated to request only necessary CT exams. Emerging Trends: Guidelines and standards are evolving that may lead to regulations for monitoring lifetime cumulative radiation dose from medical imaging sources. More attention will be focused on cancer risks for pediatric patients undergoing multiple CT scans. Additional support will go to CT research and clinical studies. New government regulations are possible, with Europe leading the way. ALARA (as low as reasonably achievable) will continue to be the goal.
  • 3. ............................................................................................................. 19RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1 COLANG, KILLION, VANO from radiologic examinations.7 In a related National Cancer Institute report, data suggested that the use of CT in adults and children has increased approximately 7 fold in the past 10 years.2 In large U.S. hospitals, CT rep- resents 10% of diagnostic procedures and accounts for approximately 65% of the effective radiation dose for all medical examinations.2 Aldrich et al conducted a study to compare the dose length product and effective radiation dose to patients from CT examinations in British Columbia, Canada.8 They compared data from 1070 CT exams and conclud- ed that considerable variation existed in the dose length product and patient radiation dose for a specific exam. This study called attention to the need to optimize the effective dose to the patient and to conduct more research to determine which additional efforts are need- ed to minimize patient exposure. Optimizing technical factors for exams can help reduce the patient radiation dose, thereby reducing risks.9,10 A pivotal study by Lee et al assessed awareness levels among patients, emergency department physicians and radiologists concerning radiation dose and the risks involved with CT scans.9 Lee and colleagues concluded that patients were not given information about the risks, benefits and radiation dose for a CT scan.9 Regardless of their experience levels, few of the participants in the study (including the emergency department physicians and the radiologists) were able to provide accurate estimates of CT radiation doses. This study underscores the prevalent lack of attention to the issue of lifetime cumulative radiation dose. This must become a central issue so that risk can be studied and monitored. One disadvantage to communicating the risk of a cumulative radiation dose would be the natural instinct of some patients to defer or cancel the exam.9 Professionals should highlight the benefits of the examination when discussing risks with the patient. Table 2 presents a list of questions and answers intended to help referring phy- sicians improve their understanding of radiation risks from medical imaging exams. CT Dose and Pediatric Patients CT remains a very important modality for diagnos- ing disorders in pediatric patients. However, children are at a greater risk because they have a longer lifetime to manifest a radiation-related cancer. Frush et al drew interesting corollaries between the widespread use of x-rays in the early days of radiography, before the damag- ing effects of radiation were understood fully, and today’s widespread use of CT on pediatric patients.11 Frush and colleagues explored the risks of low-level radiation and CT11 and advocated following the ALARA principle (as low as reasonably achievable). Their research suggested a statistically significant, increased risk of fatal cancer from low-dose radiation in the range of 50 to 100 mSv. “For example,” they wrote, “a single CT of the abdomen could provide a dose of 11 mSv. If there are 3 phases in this examination, the actual dose is 33 mSv (3 x 11 mSv). If this child is 1 of the 30% who have 3 or more examina- tions, the lifetime dose is at least 100 mSv, clearly in the range of doses associated with induction of fatal cancer.”11 Table 3 lists some common pediatric CT exams and asso- ciated radiation doses. Donnelly also drew parallels between the early decades of radiography and contemporary use of CT.12 The author pointed out the increasing use and potential misuse of examinations, the lack of attention to dose risks, particularly in children, and the delay in imple- menting dose reduction strategies, all of which combine to form an interesting parallel to the early days of radiol- ogy. One fact emerges clearly throughout the body of knowledge in radiology: Attention must be drawn to the ALARA principle, especially where pediatric patients and CT are concerned.2,11 The National Cancer Institute suggested several steps to reduce the radiation dose to children.2 First, only necessary CT examinations should be performed. Pediatricians and radiologists should consult to deter- mine whether CT is the most appropriate examination. Second, if CT is the appropriate modality, exposure parameters should be adjusted to optimize the study and minimize the dose to the patient. Specifically, radio- logic technologists should: n Limit the region scanned to the smallest possible area. n Optimize the mA settings for the organ systems to be examined (eg, lower mA for skeletal and lung exams). n Adjust technique to the child’s size and weight. n Determine appropriate scan resolution (eg, a lower resolution may be sufficient for some diag- nostic purposes).2 Physicians should minimize the use of multiple scans for contrast enhancement. Finally, radiology depart- ments should develop pediatric CT protocols that describe these steps. McLean also emphasized the importance of adjusting pediatric radiographic settings during CT to minimize dose.13 McLean summarized optimization methods and suggested that further clinical studies be conducted on
  • 4. ............................................................................................................. PATIENT DOSE FROM CT 20 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY pediatric CT dose. Despite the overwhelming public health benefits of CT, McLean suggested implementing the following steps to protect an increasing population of children from cancer risks related to CT: n Focus on scanner protocols to reduce pediatric CT dose (mAs). n Use CT scanners with automatic exposure settings to limit dose. n Develop guidelines to compare dose indicators with standards. Table 2 Questions and Answers To Help Physicians Understand Radiation Risks From CT Why is an x-ray procedure, such as a CT examination, hazardous? X-rays are high energy, ionizing radiation and will break apart DNA molecules. Light sources and microwaves have much lower energies, which are insufficient to break up molecules. What are the hazards of x-rays? The major concern from x-ray exposure is induction of cancer. Is there a safe level of x-ray exposure? There is no radiation exposure level below which the risk is zero. In general, the radiation risks are directly proportional to the amount of radiation absorbed by the patient. How long does it take for a radiation-induced cancer to be expressed? Radiation-induced leukemias have a latent period of a few years, where- as it takes decades for radiation-induced solid tumors to manifest. Do radiation-induced cancers differ from naturally occurring cancers? No, radiation-induced cancers can be detected only by epidemiologi- cal studies that compare an exposed group with a corresponding con- trol group. How does a chest CT examination compare with a chest x-ray examination? The patient dose from a typical chest CT examination (5 to 10 mSv) is more than 100 times larger than a conventional chest x-ray examina- tion (0.05 mSv). How does a chest CT examination compare with natural, background radiation? CT examination exposures generally are higher than 1 year’s worth of background radiation exposure (~3 mSv). What is the cancer risk for a patient under- going a typical CT examination? A CT scan with a dose of 10 mSv has an average cancer induction risk of about 1 in 1000, with half of those cancers being fatal (most are expressed decades after the scan). Does the age of the patient at time of exposure affect the patient risk? Definitely! Risks to children are about 3 times higher than those for a young adult. Risks to someone aged 50 years will be about 3 times lower than average. Have CT examinations been shown to cause cancer? No, as the overall cancer incidence is approximately 420 in a popula- tion of 1000; detecting a small excess (ie, 1 per 1000) would be dif- ficult in an epidemiological study. What factors should I consider prior to ordering a CT examination on a patient? It is essential to balance the radiation risks with the corresponding patient benefits. What are the general guidelines and policies for performing CT scans? Eliminate unnecessary (nonindicated) examinations and ensure that no more radiation than is needed is used to perform an examination. When is a CT scan indicated? Patient benefits should be greater than the risks. Radiologists can advise on the risks and benefits of CT scans, as well as the use of nonionizing imaging methods. How can patient radiation levels be kept as low as reasonably achievable (ALARA)? Radiological studies should be tailored to specific clinical needs. For example, a chest CT exam to assess lung disease in a child with cys- tic fibrosis would need (much) less radiation. Courtesy of Dr Walter Huda, Department of Radiology, Medical University of South Carolina, Charleston.
  • 5. ............................................................................................................. 21RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1 COLANG, KILLION, VANO n Ensure that the indicator of CT dose (CTDIvol) is visible on the dis- play console. n Include a DICOM (Digital Imaging and Communications in Medicine) file- format tag for CT dose information. n Emphasize educa- tion regarding CT protocols and dose implications. The Profession’s Position on Controlling Dose Consensus in the literature reveals mount- ing concern regarding radiation dose in CT. This is reflected in inter- national efforts to raise awareness about this issue. One group of scientists observed at a U.S. Food and Drug Administration science forum: “Our situation is given new impetus by new European and national regulations that require departments to introduce robust proce- dures for the protection of the patient, including the twin elements of ensuring clinical justification of the examination and optimization of the technique.”14 In the United States, current practice does not include tracking the cumulative lifetime dose of ion- izing radiation from medical imaging devices, nor are patients regularly informed of the risks of increased exposure to radiation from medical devices. However, this practice is beginning to shift in Europe, as evi- denced by the European Council Directive that outlines steps to ensure that patients and practitioners are edu- cated about the risks involved with radiation exposure, as well as steps to minimize the radiation dose to the patient.14 The directive, 97/43/euratom, stopped short of mandating a record of the actual patient dose, not- ing that “Medical exposure continues to constitute the major source of European Union citizens’ exposure to artificial sources of ionizing radiation. However, the use of ionizing radiation has allowed great progress in many areas of medicine. It is therefore essential that practices involving medical exposure are carried out in optimized radiation protection conditions.”14 Similar efforts are underway in the United States to optimize procedures and thereby minimize radiation dose to the patient. Stern et al cited 9 proposed changes to the U.S. Performance Standard for Diagnostic X-Ray Equipment that will reduce unnecessary radiation emit- ted during fluoroscopy.10 These are steps in the right direction but, like the European Council directive, fall short of fully regulating the measurement of patient radiation dose. A search of the literature did not reveal consensus among researchers regarding how these steps could be implemented in widespread practice. The literature also underscores the need to develop and adopt reference dose standards for CT examina- tions. For example, Mayo et al found that large varia- tions exist in technical factors used in pediatric chest CT.15 They encouraged radiology departments to adopt reference dose value standards for these exams. Adopting these standards could benefit all patients undergoing CT exams. The Role of Information Technology Lacking in the literature is any mention of how the medical imaging community will implement a cradle-to- Table 3 Approximate Radiation Dose by Pediatric Exam Type and Organ Exam Type Relevant Organ Approximate Equivalent Dose to Relevant Organ (mSv) Pediatric head CT scan unadjusted settingsa (200 mAs, neonate) Brain 60 Pediatric head CT scan adjusted settingsb (100 mAs, neonate) Brain 30 Pediatric abdominal CT scan unadjusted settings (200 mAs, neonate) Stomach 25 Pediatric abdominal CT scan adjusted settings (50 mAs, neonate) Stomach 6 Chest x-ray (PA/lateral) Lung 0.01 / 0.15 Screening mammogram Breast 3 a “Unadjusted” refers to using the same settings as for adults. b “Adjusted” refers to settings adjusted for body weight.
  • 6. ............................................................................................................. PATIENT DOSE FROM CT 22 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY grave radiation dose monitoring system. As discussion about tracking lifetime radiation dose from CT and other imaging modalities begins, a wide range of policy and technology changes will have to coalesce to develop the future model. First, government entities might consider including radiation dose in patients’ permanent medical records. Second, radiology personnel, physicians, nurses and other allied health workers must receive education and training to understand the importance of good management of patient doses. Limiting lifetime patient cumulative dose should be a goal, with the understanding that occasionally there will be medical reasons to justify the use of a higher dose. Additional education and train- ing will be needed to help health care professionals better inform patients of the risks involved. Finally, a partner- ship of technologies and standards will have to be formed to allow the practice to change. As these changes find their way into the workplace, it will be necessary to develop a mechanism by which imaging equipment can transmit patient absorbed dose data to the radiology information system (RIS) or the picture archiving and communications system (PACS). Modern digital radiology equipment produces images with the dosimetric information contained in the DICOM header file. Vano et al pointed out that cooperation between the International Electrotechnical Commission and the radiology industry regarding stan- dardization of the DICOM header will enable auditing of x-ray procedures and patient dose.16 An immediate benefit of this effort would be automatic records that would reference comparison dose values and trigger an alarm if 1 of the monitored parameters was outside of an acceptable range.16 A review of the literature reveals a gap in how this information would be transmitted from the imaging device to a monitoring and archiving system. A pos- sible model could include the RIS or the PACS trans- mitting the dose information to the personal health record, the enterprise health record or a regional health organization. At this point, the literature does not indicate which regulatory body would be the ulti- mate custodian of this data. A future model would need to describe how dose information from all medi- cal imaging centers would be routed to a central data store for a patient. Careful evaluation and planning would be needed to provide a seamless transport conduit for these data. Health Insurance Portability and Accountability Act constraints regarding patient privacy could prove to be a challenge to implementing this model. Another possible constraint could be the cost of implementing a national model and developing a regulatory board to govern its policies. One proposed model uses technology within the imaging device to transmit the dose information in real time to the PACS via DICOM using the modality- performed procedure step, or a newly proposed struc- tured report within DICOM.16 Important work has been done in this area by Vano et al, who suggested an online audit of the actual dose by comparing the dose to a diagnostic reference level.17 “According to the International Commission on Radiological Protection, the average patient dose for a specific examination type should be compared with the diagnostic reference level for the examination.”16 Vano and colleagues proposed a tool to identify any abnormal patient dose and determine the cause of the overexposure.17 Their report describes the benefits and results derived from this model of online quality control. The authors proposed generating real-time alarms when baseline minimum doses were reached. In computed radiography, the exposure index would be audited. In interventional radiology, dose area product, number of images per series, total number of series and total num- ber of images per procedure also would trigger an alarm if studies exceeded the baseline parameters. Additional research is required to determine whether real-time alarms for excessive doses are effective as an optimiza- tion technique. DICOM Component The DICOM standard was created by the National Electrical Manufacturers Association to enable trans- mission and viewing of medical images. DICOM has become the accepted conduit for transmitting medi- cal image data throughout the world. Part 10 of the standard describes a file format for the distribution of images. Balter et al examined a variety of technical information describing image acquisition.18 These data can be found in the DICOM headers of digital images. The authors described placing key exposure data in various public data elements and private fields. Because no standard currently exists, the exact location of this information depends on the manufacturer. Table 4 dem- onstrates an example of DICOM tags in the header of a generic flat panel. According to Balter and colleagues, efforts are underway to standardize the architecture for digital fluoroscopy: “A cooperative effort between the International Electrotechnical Commission and the DICOM committee is currently defining those dosimet- ric elements that should be stored for every examination
  • 7. ............................................................................................................. 23RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1 COLANG, KILLION, VANO performed using ‘digital’ [sic] x-rays and its storage structure within DICOM public fields.”18 Downstream Data Repositories Currently, there is no standard for acquir- ing, evaluating and archiving digital imaging data. Until a standard is implemented, important research needs to be done concerning proto- type practice standards that permit dissemination of these data. Equipment manufacturers will need to reach consensus on a standard. Vano et al found that, at present, manufacturers of x-ray systems differ in how they populate the content of dosimetric information in the DICOM header.16 Downstream data reposi- tories could consist of RIS, PACS or any other subordinate system that would receive data from the modality. Dose data from the DICOM object could be transmitted electronically using a standardized format to a national data store or to a patient’s personal health record or enterprise patient medical record. Figure 1 describes how image acquisi- tion data could be transmitted to a national database or to RIS or PACS from the DICOM object. Future Directions A plethora of data implicates medical sources as the public’s number 1 source of exposure to ionizing radia- tion. “In the 2000 report of the United Nations Scientific Committee on the Effects of Atomic Radiation, it was stated that medical applications of ionizing radiation rep- resented by far the largest man-made source of ionizing radiation exposure.”19 Despite the fact that the benefits to the patient are enormous, lifetime cumulative exposure risks must be addressed. A search of the literature did not reveal any current requirements in the United States or Europe to track and monitor lifetime cumulative radiation dose to patients from medical imaging techniques such as CT and fluoroscopy. In the absence of requirements, a call is emerging for additional studies to describe the most efficient way to address this issue. The literature search did not reveal any effort to standardize key reporting vari- ables in the United States, nor did it reveal consensus on efforts to standardize optimization methods and practices. One important aspect in understanding dose report- ing is that recording individual irradiation events is not sufficient for documentation purposes. Several regula- tory bodies in different countries have recommended recording accumulated dose values such as the “dose at the reference point” or the “dose area product” per pro- cedure. However, to complete dose reporting require- ments, a distinct set of accumulated values must be provided to fulfill legal requirements for “recording of accumulated values applied during a procedure.”19 Although definitions of diagnostic reference levels vary, they share common elements that include dose levels, standard-size patients or phantoms, dose quantity and specific equipment.20 A recent article by Seeram and Table 4 Sample Data From DICOM Tags in the Header of a Chest Flat Panel (0008,0020) Study date 7/01/03 (0008,0030) Study time 10:31:12 (0008,0033) Image time 10:32:43 (0010,0020) Patient ID NNNNNNN (0010,0040) Patient’s sex F (0010,1010) Patient’s age 085Y (0018,0015) Body part examined Chest (0018,0060) kVp 125 (0018,1150) Exposure time 5 (0018,1151) X-ray tube current 250 (0018,115E) Image area dose product 0.83557 (0018,1190) Focal spot(s) 0.6 (0018,1405) Relative x-ray exposure 61 (0018,7060) Exposure control mode AUTOMATIC (0018,7062) Exposure control mode description AEC_left_and_right_cells (0028,0010) Rows 2022 (0028,0011) Columns 2022 (0028,0100) Bits allocated 16 (0028,0101) Bits stored 14
  • 8. ............................................................................................................. PATIENT DOSE FROM CT 24 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY Brennan underscored the need for optimization and use of diagnostic reference levels (DRLs).20 Their article focused on managing patient dose in diagnostic radiol- ogy by using DRLs, along with principles for optimizing radiation protection. DRLs must be relevant to the locale where they are applied and should be determined from radiation dose survey data.20 The article discussed the 2 triads of radiation protection — principles (ie, optimiza- tion, justification and dose limitation) and actions (ie, time, distance and shielding). According to Seeram and Brennan, DRLs should be considered a dynamic param- eter, and hospitals should perform regular dose surveys to ensure that levels remain applicable to new hospital equipment.20 The authors sug- gested that a variety of param- eters be examined when conducting a dose survey, including examination type, the number and type of hos- pitals involved, phantom and patient investigations, dosime- try methods, establishment of the reference level and acces- sory information.20 Seeram and Brennan were careful to point out that, although opti- mization of the technique is an important step in limiting patient dose, care should be taken to ensure image quality remains high. DRLs are a step in the right direction to standard- ize practice. The literature reveals that attention is beginning to focus on how radiology professionals could communicate and handle lifetime cumulative radiation dose from medical imaging devices. For now, Europe continues to lead the way in implementing a standard of practice for monitoring cumulative radia- tion dose from medical imaging. Supplement 94 of the DICOM Standards Committee, Working Group 6, Base DICOM is used to transmit the dose informa- tion via the MPPS (modality- performed procedure step) or through radiation dose structured report in DICOM using an indus- try accepted standard (IEC and DICOM). Is a national, regional or enterprise patient dose database available? Does the patient have a PHR (personal health record)? Patient cumulative dose could be added to radiology informa- tion system or PACS. (RIS or PACS must be implemented to accept these data.) Patient cumulative dose is added to data store using future standard messaging technology. Cumulative dose data written in PHR using an Extensible Markup Language standard such as XML. Imaging modality such as CT or other computerized radiology system generates dose information in “real time” as the patient’s image is acquired. Yes Yes No No END END Figure 1. Sample data flow from the CT scanner to a downstream data warehouse or personal health record.
  • 9. ............................................................................................................. 25RADIOLOGIC TECHNOLOGY September/October 2007, Vol. 79/No. 1 COLANG, KILLION, VANO 5. Berland LL, Smith JK. Multidetector-array CT: once again, technology creates new opportunities. Radiology. 1998;209(2):327-329. 6. Golding SJ, Shrimpton PC. Radiation dose in CT: are we meeting the challenge? Br J Radiol. 2002;75(889):1-4. 7. Nagel H, Galanski M, Hidajat N, Maier W, Schmidt T. Radiation exposure in computed tomography: fundamen- tals, influencing parameters, dose assessment, optimiza- tion, scanner data, terminology. Paper presented at the COCIR 2000, Frankfurt, Germany. 8. Aldrich JE, Bilawich AM, Mayo JR. Radiation doses to patients receiving computed tomography examinations in British Columbia. Can Assoc Radiol J. 2006;57(2):79-85. 9. Lee CI, Haims AH, Monico EP, Brink JA, Forman HP. Diagnostic CT scans: assessment of patient, physician, and radiologist awareness of radiation dose and possible risks. Radiology. 2004;231(2):393-398. 10. Stern S, Tucker S, Gagne R, Shope T. Estimated benefits of proposed amendments to the FDA radiation-safety stan- dard for diagnostic x-ray equipment. Paper presented at the 2001 FDA Science Forum, Washington, DC. 11. Frush DP, Donnelly LF, Rosen NS. Computed tomography and radiation risks: what pediatric health care providers should know. Pediatrics. 2003;112(4):951-957. 12. Donnelly LF. Lessons from history. Pediatr Radiol. 2002;32(4):287-292. 13. McLean D. Computed tomography doses in children. Lancet. 2004;363(9416):1178. 14. Radiological protection for persons undergoing medical examination or treatment. Europa Web site. www.europa. eu/scadplus/leg/en/cha/c11546b.htm. Updated August 17, 2006. Accessed July 4, 2006. 15. Mayo JR, Aldrich J, Muller NL; Fleischner Society. Radiation exposure at chest CT: a statement of the Fleischner Society. Radiology. 2003;228:15-21. 16. Vano E, Padovani R, Neofotistou V, et al. Improving patient dose management using DICOM header information. The European SENTINEL experience. itab2006 International Congress, Greece, 2006. 17. Vano E, Fernandez JM, Ten JI, Gonzalez L, Guibelalde E, Prieto C. Patient dosimetry and image quality in digital radiology from online audit of the x-ray system. Radiat Prot Dosimetry. 2005;117(1-3):199-203. 18. Balter S, Vano E, Gonzalez L. Fluoroscopic patient dosim- etry from dicom headers. 11th International Congress of the International Radiation Protection Association. Madrid, Spain, 2004. 19. International Atomic Energy Agency. International action plan for the radiological protection of patients: report by the Director General. wwwns.iaea.org/downloads/rw /radiation-safety/patientprotactionplangov200236gc4612 .pdf. Accessed July 3, 2006. 20. Seeram E, Brennan PC. Diagnostic reference levels in radi- ology. Radiol Technol. 2006;77(5):373-384. Standard, proposes a standard for capturing these data during image acquisition.21 Conclusion The use of MDCT is on the rise and accounts for a large percentage of patient radiation exposure from medical imaging devices. A growing number of research- ers in the medical imaging community are calling for heightened awareness of patient radiation dose from CT and other medical imaging radiation sources. Efforts are underway to examine methods and practices to allow the profession to reduce patient radiation exposure and track the lifetime cumulative radiation dose. Technical com- ponents will have to be standardized and implemented throughout the imaging community. Using DICOM as the principal transmission agent, a modality-performed procedure-step object or a newly proposed structured report template could be used to transmit patient radia- tion data downstream to a recipient PACS, RIS, personal health record, enterprise health record or yet-to-be- defined entity or object. Several technical and procedural issues remain and are not described fully in the literature. In addition, further research is needed to deter- mine the most appropriate method to develop and implement best practices that minimize exposure to patients by optimizing technical factors. More research also is needed on how to evaluate the efficacy of imple- menting a national radiation dose database to monitor a patient’s lifetime exposure to ionizing radiation from medical imaging devices. Radiology professionals, as well as the general public, should educate themselves regarding the most effective ways to monitor patient cumulative radiation dose from CT and other medi- cal imaging sources. In the interim, the focus should remain on optimizing image quality while conveying a minimal radiation dose to the patient. References 1. Aldrich J, Williams J. Change in patient doses from radio- logical examinations at the Vancouver General Hospital, 1991-2002. Can Assoc Radiol J. 2005;56(2):94-99. 2. Radiation risks and pediatric computed tomography (CT): a guide for health care providers. National Cancer Institute Web site. www.cancer.gov/cancertopics/causes/radiation- risks-pediatric-CT. Published August 20, 2002. Accessed October 6, 2006. 3. Yoshizumi TT, Nelson RC. Radiation issues with multidetec- tor row helical CT. Crit RevComput Tomogr. 2003;44(2):95-117. 4. Vano E, Gonzalez L. Avoiding radiation injuries from inter- ventional fluoroscopic procedures. Eur Radiol Supplements. 2004;14:59-66.
  • 10. ............................................................................................................. PATIENT DOSE FROM CT 26 September/October 2007, Vol. 79/No. 1 RADIOLOGIC TECHNOLOGY 21. Digital imaging and communications in medicine (DICOM): supplement 94: diagnostic x-ray radiation reporting dose special report (2005). Rosslyn, VA: DICOM Standards Committee. John E. Colang, M.S.R.S., R.T.(R), PMP, is a project manager for digital health projects with Intel Corporation in Albuquerque, New Mexico. Jeff B. Killion, Ph.D., R.T.(R) (QM), is an associate professor in the department of radiologic science at Midwestern State University in Wichita Falls, Texas. Eliseo Vano, Ph.D., is a professor of medical physics in the radi- ology department at Complutense University in Madrid, Spain. Reprint requests may be sent to the American Society of Radiologic Technologists, Communications Department, 15000 Central Ave. SE, Albuquerque, NM 87123-3909. ©2007 by the American Society of Radiologic Technologists.