Dr. Shrestha is Vice President, Medical Information
Technology, University of Pittsburgh Medical Center, Pittsburgh, PA; and
Medical Director, Interoperability & Imaging Informatics,
Disclosures: Dr. Shrestha is a Founding
Member Executive Advisory Program at GE Healthcare, is on the Medical
Advisory Boards of Nuance, Inc., and Vital Images, Inc., as well as on
the Editorial Board of Applied Radiology, and the Advisory Board of KLAS Research.
Godfrey Newbold Hounsfield was an English electrical engineer credited
with developing the diagnostic imaging technique of computed tomography
(CT) and with creating the first commercially viable CT scanner in
Hayes, England, back in 1972. Sir Hounsfield would no doubt be proud of
the success of this technology in health care. Thanks to his invention,
exploratory surgery, once commonplace in ‘diagnostics,’ is now a rare
procedure. Undoubtedly an invaluable diagnostic tool, the number of CT
examinations ordered in the United States(U.S.) has grown from 26
million in 1998 to 85.3 million in 2011.1 Medical exposure
to ionizing radiation constitutes nearly half of the total radiation
exposure of the U.S. population from all sources. Americans are exposed
to > 7 times as much ionizing radiation from medical procedures today
than during the early 1980’s, due in most part to the higher
utilization of CT.2
While the trajectory in the growth
of CT volume is not as steep as the double-digit growth experienced in
the 2000s, the continued upward trend in usage and the direct
correlation to increased risk of cancer opens up CT radiation dose
management to many opportunities to find the perfect balance between the
acceptance of the risks associated with radiation versus the benefits
to be gained from the use of radiation.
Fundamentals of dose parameters: A push towards personalized dose protocols
A significant part of the challenge of patient dose management in CT arises from the fact that overexposure in CT is frequently not detected.
In contrast to film-based radiography, where overexposure results in a
dark image, increasing dose in CT and other digital imaging techniques
results in images with less noise (improved visual appearance) and fewer
streak artifacts, although not necessarily with greater diagnostic
information. Hence, we often find that image quality in CT often exceeds
the clinical requirements for diagnosis.
This of course points to
the importance of being able to accurately measure and quantify the
radiation dose. While the ultimate goal is a personalized approach to
radiation dose management, we have to start with the basics. All CT
units display the Computed TomographyDose Index (CTDI), a measure of the
quantity of radiation output by the scanner for a particular study.
This is often displayed alongside the dose length product (DLP), which
is an indicator of the integrated radiation dose of an entire CT
These measurements, however, are based on measuring
the absorbed dose in a cylindrical acrylic phantom with a 10-cm pencil
ion chamber in the phantom’s center hole and again in one of the
phantom’s peripheral holes. This is arguably practical, but it is not
personalized to the specific patient.
Radiation dose units include
absorbed dose, which is the energy absorbed per unit mass of tissue;
equivalent dose, which takes into account the radiation weighting
factor; and effective dose, which takes into account the relative
sensitivities of various tissues to radiation. The effective dose allows
the health care provider to make an estimate of relative patient risk.
every patient is unique, and data from phantom-based simulations is not
quite the real thing, since most of the data is averaged out and less
specific. This is pushing for a level of scanning protocol optimization
and dose personalization that we have not seen before.While most CT
scanners do a good job of reporting the amount of energy they emit, it
often takes sophisticated analysis to determine what this means at a
personalized level to each patient.
Going beyond the headline news
hype around radiation dose exposure has reached an all-time high with
the increasing use of airport scanners and threats to boycott the scans
and opt for pat-downs instead. While airport scanners are worthy
catalysts for debate on radiation dose management, the reality is that
these are, in the larger scheme of things, quite harmless. One scan from
a typical “backscatter” security scanner might deliver 0.005to 0.01
millirem—far below the 10,000 millirem considered the danger threshold. A
traveler would require > 1,000 such scans in a year to reach the
effective dose equal to one standard chest x-ray.
News related to
radiation dose and CT scanning often hits the media in the worst ways
possible, and unfortunately, makes the headlines quite often. In 2008,
Cedars-Sinai Medical Center in Los Angeles revealed that, over a period
of 18 months, 206 patients received 8 times the dose normally delivered
using a CT brain-perfusion scan. This exacerbated nationwide concerns
that patients are exposed to excess radiation during medical testing. A Los Angeles Times article
about the incident described the scanner error in almost Hollywood
terms: Somebody should have noticed. But nobody did—everybody trusted
But these attention-grabbing headlines
are not far and few in between. The radiation overdoses point to a
problem well-documented in medicine over the last decade—the need for
multiple backup systems to catch mistakes and a more organized approach
to managing CT utilization.
Managing CT utilization
exposure from CT scans is cumulative over a patient’s lifetime. The
risk associated with a radiation dose from a single CT scan is
relatively small when compared with the clinical benefit of the
procedure. But patients are increasingly undergoing multiple CT scans
and other radiation-based procedures, which can lead to unnecessary
radiation risk. The increasing utilization can be categorized into 3
- Appropriate imaging: targeted
towards expedience of diagnosis and more often based on satisfying
appropriateness criteria as defined by the American College of Radiology
- Inappropriate imaging: mostly variants of defensive medicine, patient demands and even self-referrals; and,
- Screening exams.
Handling the challenges of increased CT utilization can be boiled down to 3 basic areas:
- Imaging appropriateness and decision support: The ACR advises that no imaging exam should be performed unless a clear medical benefit outweighs any associated risk.
- Dose optimization: This
entails choosing imaging parameters and performing the exams to yield
optimal diagnostic information while minimizing overall dose to the
- Dose limitation: This includes ensuring that we
keep dose to the patient ‘as low as reasonably achievable’ (ALARA), a
guiding principle that requires the lowest radiation dose that will
yield the most appropriate image quality for a particular patient to
enable the correct clinical decision.
Pediatric imaging and dose management challenges
Numerous academic publications and other print media have highlighted startling statistics about children and CT imaging. JAMA Pediatrics recently
published the results of the HMORN Cancer Research Network (CRN) study
that tracked an increase in CT use over a15-year period.4 It
was found that increased use of CT in pediatrics, combined with the
wide variability in radiation doses, resulted in many children receiving
a high-dose examination. The researchers projected that the 4 million
CT scans of the head, abdomen/pelvis, chest or spine in the U.S.
pediatric population could cause 4,870 future cancers. They also stated
that this number could be reduced dramatically—by62%—if doses were
reduced by using standardized protocols and guidelines, such as Image
Gently, and by eliminating unnecessary imaging.
The use of CT
doubled for children under age 5 and tripled for children aged 5 to 14
between 1996 and 2005. CT use remained stable in2006 and 2007, and then
began to decline. Startling, too, was the variability in the radiation
doses administered where effective doses varied from 0.03 to 69.2 mSv
A now famous separate Duke study5 from 2000
to 2006 found that while the pediatric emergency department (ED) patient
volume increased in that time period by just 2%, and triage acuity
remained stable, the number of pediatric ED scans increased by 435% for
chest CTs and 366% for cervical spine CTs. These findings were shocking,
given that children are at greater risk from a given dose of radiation
compared with adults due to their body’s increased radiosensitivity and
the greater period of time in which to manifest these changes.
Obesity and CT radiation dose risks
patients often face higher radiation exposure from CT scans. Research
shows that the internal organs of obese men receive 62% more radiation
during a CT scan than those of average-weighted men.6 Often,
when technicians use normal equipment settings to performa CT scan on an
obese patient, the resulting images are blurry, as the x-ray photons
have to travel further and make their way through extra layers of fatty
tissue. As a result, the equipment is adjusted to a more powerful
setting, producing better image quality, but exposing the obese patient
to unnecessary additional radiation. There is, however, promising work
being done on personalized phantoms and ultra-realistic, 3-dimensional
computer models of patients, resulting in much more accurate and
State dose legislation: The California effect
October 2010, California Gov. Arnold Schwarzenegger signed a new
radiation patient protection law that mandates strict procedures and
reporting requirements for CT scanners and radiation therapy procedures,
as well as reporting of radiation overdoses to the state Department of
Public Health. All CT systems must record the dose of radiation on every
study by putting the data directly in the radiology report or attaching
the protocol page to the actual radiology report. Connecticut and Texas
have already followed California’s example with their own legislation;
other states are expected to enact similar reporting requirements.
Modality vendor innovations
differentiating CT capabilities, dose is now king. The CT-slice wars
have now given way to the dose wars among modality vendors, and this is
deemed a positive development.
Providers have become more
discriminating regarding dose-reduction strategies, resulting in dose
moving up the decision tree and becoming very influential in new CT
purchases. Improvements in dose management technology are evident in
most CT scanners, particularly in the next-generation systems.
modality vendors are getting creative and innovative around
radiation-dose reduction and management. GE’s VCT and the Discovery
CT750 HD CT scanners received kudos for their dose-reduction
capabilities and ASiR (Adaptive Statistical Iterative
Reconstruction)technology. Philips is approaching dose reduction with
better protocols and image reconstruction. The company’s Brilliance iCT
256 scores highly, and there is much progress made with the iDose and
iDose4 packages. Siemens is being viewed as another leader in dose
optimization. The company’s plus points include development of IRIS and
SAFIRE (iterative reconstruction), with dose optimization
technologies,such as CARE Dose 4D. Toshiba is providing software
upgrades that allow reduced dose and faster procedure speeds, especially
on the Aquilion ONE 320-detector row CT.
Add-on or packaged
iterative reconstruction software is now proven to reduce noise while
creating a clearer CT image at a lower dose.Recent studies have shown
significant reduction of radiation dose, up to 40% to 50%, with some
vendors claiming a 50% to 70% CT dose reduction with no compromise in
image quality and diagnostic value.
cry for better innovation in radiation dose reduction continues to be
heeded, and every year, we see progressive advancements in various
areas. Some of the highlights include:
excessive radiation exposure before it occurs by using a unique software
platform (DoseMonitor™ PHS Technologies Group,LLC ), which identifies
patients who may be at risk for ionizing radiation overexposure at the
time a test is ordered.7
- Automatic tracking of radiation dose exposure, with patient-size adjusted dose correction.8
- Automated extraction of radiation dose information for CT.9
ability to extract information from dose sheets produced by legacy CT
scanners that cannot generate DICOM radiation dose structured reports.
ACR’s National Radiology Dose Registry,10 which
started as a pilot program, now entails an improvement process that
includes more vendors, incorporates patient size, and ongoing work with
Integrating the Healthcare Enterprise (IHE) on Radiation Exposure
Future of dose management
effective management of radiation dose has a broad set of needs across
health care domains, as represented in Figure 1. Minimizing unnecessary
radiation is becoming a priority for medical imaging facilities,
especially with increasing oversight now commonplace from state
regulatory agencies and accrediting bodies. A significant driving force,
too, is value-based imaging, with imaging appropriateness being a key
Perhaps the lowest-hanging fruit in the journey to
effective CT radiation-dose management is broadening awareness,
including heightened patient and public education, stating the facts,
and clearing the confusion. A number of professional association
initiatives have a lotto offer, and these include the Image Gently
alliance, which raises awareness of opportunities to lower radiation
dose in the imaging of children; the Step Lightly campaign for
interventional dose reduction; and the Image Wisely campaign, an
ACR-RSNA task force on radiation protection for adults.
sophisticated and expensive equipment become available in hospitals and
imaging centers, there are inevitable pressures to expand applications.
Today, we are seeing an increase not just in the utilization of CT scans
but also in the wider availability of CT scanners and an increasing set
of indications for CT use. This subsequently leads to a rapid increase
in the number of protocols, and, ultimately, to protocol variance and
complexity. As a responsible industry, we must continue to push for
greater levels of personalized dose-management capabilities and
automation along with technological advancements in every facet of the
CT imaging workflow.
- 2012 CT market outlook report. IMV Medical Information Division. http://www.imvinfo.com/index.aspx?sec=def&sub=dis&pag=dis&ItemID=200081. Accessed August 6, 2013.
- Ionizing radiation exposure of the population of the United States. National Council on Radiation Protection & Measurements. NCRP. http://www.ncrppublications.org/reports/160.Accessed August 6, 2013.
- Zarembo A. Cedars-Sinai radiation overdoses went unseen at several points. Los Angeles Times. http://articles.latimes.com/2009/oct/14/local/me-cedars-sinai14. Updated October 14, 2009. Accessed August 1, 2013.
Miglioretti DL, Andrew Williams A. The use of computed tomography in
pediatrics and the associated radiation exposure and estimated cancer
risk. JAMA Pediatr. 2013;167:8.
- Broder J, Fordham LA, Warshauer DM. Increasing utilization of computed tomography in the pediatric emergency department. Emerg Radiol. 2007;14:227-232.
Ding A, Mille MM, Liu T, et al. Extension of RPI-adult male and female
computational phantoms to obese patients and a Monte Carlo study of the
effect on CT imaging dose. Phys Med Biol. 2012;57:2441-2459.
- DoseMonitor. DoseMonitor™ PHS Technologies Group, LLC. www.dosemonitor.com. Accessed August 1, 2013.
- Image Safely. www.imagesafely.com. Accessed August 1, 2013.
- Radiation Dose Intelligent Analytics for CT Examinations. www.radiancedose.com. Accessed August 1, 2013.
Dose Index Registry. Am Coll Radiol.
Accessed August 1, 2013.