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Current Trends in CT Dose Reduction - 2013

71st CSRT Annual Conference

Daniel DeMaio

on 1 October 2015

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Transcript of Current Trends in CT Dose Reduction - 2013

Dose Reduction in CT
Radiation Dose & CT
-the current state-
Daniel N. DeMaio

Tech error during CT neck - child burned

CT perfusion overdose at Cedar-Sinai Hospital

Walt Bogdanich series in the NY Times
CT Technologist
Physicians & researchers
Patients & the media
Recent Media Coverage
Improved Outlook...
1. National initiatives to reduce dose:
Amis, ES. CT Radiation Dose: Trending in the Right Direction. Radiology 2011; 261(1): 5-8.
Levin DC, The Recent Downturn in Utilization of CT: The Start of a New Trend?. JACR 2012; 9:795-798
Are We There Yet?
CT Utilization in the U.S
Study of a major HMO:
1996: 52 CT exams per 1,000 patients
2010: nearly triples to 149 CT exams^
^Smith-Bindman, R., Use of diagnostic imaging studies and associated radiation exposure for patients enrolled in large Integrated Healthcare systems, 1996-2010. JAMA. 2012; 307(22): 2400-2409.

*IMV Market Research CT,
CT and Radiation Dose
Annual radiation exposure in US is 7-times greater in 2006 compared to the 1980's.^

More than 45% of the effective dose from medical radiation exposure is attributed to CT.*

As many as 29,000 new cancers in US may be related to CT exams in 2007.~
^National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States (2009). NCRP report no.160. Bethesda, Md: National Council on Radiation Protection and Measurements, 2009.

*Fazel R, Exposure to low-dose ionizing radiation from medical imaging procedures. N Engl J Med 2009; 361:849-57.

~Berrington de Gonzalez, A, Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch Intern Med 2009; 169:2071-7.
3. Innovations from vendors
Image Gently & Wisely
ACR Appropriateness Criteria and CT Dose Index Registry
CT utilization in the ER (Medicare)

The Lancet (June 2012)* - increased risk of leukemia & brain tumors

Institute of Medicine (IOM) - avoid CT examination to reduce the risk of breast cancer. ^
*Pearce, MS, Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. The Lancet, Early Online Publication, 7 June 2012 doi: 10.1016/

^Smith-Bindham, R. Environmental causes of breast cancer and radiation from medical imaging. Arch Intern Med. Online, 11 June 2012 doi:10.1001archinternmed.2012.2329
What is the technologist position in the ongoing CT dose controversy?
We need to focus on:
Effective communication with patients, physicians, and other colleagues.
Elimination of errors
Dose reduction techniques
Practical methods of CT dose reduction:
System-based methods of CT dose reduction:
Precise beam control
Substantial beam filtration
Automatic Tube Current Modulation
Automated Tube Potential Selection
Detector efficiency
Iterative reconstruction
Dual-energy CT
Protocol design & adaptation
Clinical Indication
Diagnostic Goal
Customized Protocol
Patient age, sex, and dimensions
Required phases of contrast enhancement
Customization of Protocols
still asks,
"What technique do I use?"
How to optimize?
"Smart-Tech" Protocol
Conspicuity of pathology
Tolerable noise level
To shield or not to shield?
Summary of Dose Reduction Strategies

Limit acquisition phases to the bare minimum
Protocol Design
Make adjustments for every case - customize!
Turn up the noise...
More noise = less dose
How much noise will the indication (& the radiologist) tolerate?
Kalra, MK, Pointers for optimizing radiation dose in abdominal CT protocols. JACR 2011 Oct;8(10):731-4.
mAs = mA x time
Direct & linear relationship with patient dose
Use half the mAs and dose decreases by one-half (noise increases 40%)
Make reductions that are age-specific, size-specific, and "indication-specific."

Optimize protocols using CTDIvol
Coakley F V et al. AJR 2011;196:619-625
No Picasso's!
Singh S., JACR 2011; 8(5):369-372
Yu L et al. Radiographics 2011;31:835-848
440 mAs
80 mAs
Tube Potential (kVp)
Remember the 15% rule?
Reducing kVp from 140 to 120 results in a 35-40% dose savings
As kVp decreases, noise and contrast increase
CTA's - try 80-100 kVp
Perception is reality.....
"Play your CT system" like a finely-tuned instrument
Other Considerations
Empowered Technologists Adjust Protocols
"Experienced CT technologists can make significant dose-reducing modifications while maintaining diagnostic image quality."
Coakley FV, CT Radiaton Dose: What Can You Do Right Now in Your Practice? AJR 2011, 196:619-625
Scan Time
Table Speed
Scan Length
Dose Length Product (DLP)
Avoiding Repeats
Above and below patient
Always use when possible
Little risk when used correctly
Place after scout(s)
Keep out of acquisition volume
In-plane bismuth shields:
Arms up!
can effectively reduce organ dose - breast, thyroid, orbits, etc.

may improve patient comfort & confidence
wastes radiation and decreases signal

causes some streak artifact

risk of AEC malfunction
One Verdict:
"...the ways in which bismuth shielding can hurt outnumber the ways in which it helps. Equally or more effective alternatives exist to minimize radiation dose to the breast, thyroid, and lens of the eye without degrading image quality or wasting dose."
McCollough CH, Bismuth Shields for CT Dose Reduction: Do They Help or Hurt? JACR 2011, 8(12):878-879
The responsibility is ours....
Daniel N. DeMaio
University of Hartford
Thank you!
A word of caution:
"Increasing radiation causes a very small statistical future societal increased risk of cancer. Lowering radiation for a CT scan creates
a very real immediate risk
to the specific patient...

This is the risk of
missing the correct diagnosis
because the exposure factors are too low and image quality is poor."
Cohen MD. CT Radiaton Dose Reduction: Can We Do Harm by Doing Good? Pediatr Radiol 2012, 42:397-398
March 28, 2015
During CT of the chest, the glandular dose exceeds MQSA's recommended maximum of 3 mGy. Therefore the author's state:

" plane breast shielding remains a feasible and effective technique for breast protection."
Zhang J & Oates ME. CT Bismuth Breast Shielding: Is It Time to Make Your Own Decision? JACR 2012, 9(12):856-858
Major themes:
The state of CT use, dose, and risk.

Overview of system features designed for dose reduction.

The practical methods of CT dose reduction:
NCRP Report 160
Fixed mAs - How low can you go?
240 vs. 80 mAs
Protocol Optimization
Determine an acceptable noise level based upon the specific patient & exam indication.
Adjust mAs & kVp accordingly
"Cheat" with kVp - lower it when possible (high contrast)
Radiation Protection 101 - shorten time & SHIELD!
Master the use of every dose reduction tool available.
Learn how the features of your system work best together.
CT Protocol
Aim for >1
Keep an eye on the mAs!
Pitch &
Reduces dose, but increases noise!
*Also decreases z-axis resolution...
Decrease that gantry rotation time!
Use the CTDIvol and noise index as a guide
Limit z-axis coverage:
Abd/pel - top of diaphragm to inferior pubic symphysis
Kidney Stone Protocol - start at top of kidneys
CTPA - don't include adrenals
The key metric of absorbed dose to the patient
DLP = CTDIvol x scan length
Minimize that scan length!
Don't overscan just to "be sure."
Arms should be raised whenever possible!
Decreases streak artifact
Can substantially reduce dose with AEC
Goals of the presentation:
*Levin DC, The Recent Downturn in Utilization of CT: The Start of a New Trend? JACR 2012; 9:795-798
for Medicare patients
for private offices*
2. Downturn in utilization?
Beam Control
Filtration of the CT Cone Beam
System Innovations & Practical Techniques

Precise beam that only umbra remains...
SmartTrack Dynamic Collimation (GE)
Flying Z-Axis Focal Spot (Siemens)
Lead Shielding
Optidose Z-Axis Tracking (GE) & Brilliance iCT Dynamic Collimation (Phillips)
Reducing mAs
176 mAs
256 mAs
88 mAs
Inherent Filtration
3 mm Al equiv.

Added Filtration
Flat copper (2-3 mm Al)
Beam shaping (2-3 mm Al)
Total filtration of the CT beam: 8-9 mm Al equiv.
"Bowtie Filter"
Adapts beam intensity to match patient shape.
"Phototiming" for CT
Automatic Exposure Control (AEC) for CT

Automatic Tube Current Modulation (ATCM)

Automatic Dose Control (ADC)
Types of ATCM
Longitudinal dose modulation
2 types of ATCM

Angular dose modulation
X-Y axis

Temporal dose modulation
Nagel, DN. (2007) CT Parameters that Influence the Radiation Dose.
Automated Tube Potential (kVp)
Based on topographic localizer (scout).
mAs adjusted along the z-axis.
Siemens "Definition" CT systems
Automatic determination of the optimal mAs & kVp combination
Based upon the study type, region, habitus, etc.
System analysis of localizer (scout)
Auto kVp
120 kV, mAs 199
CTDI = 15.31 mGy
CARE kV, mAs 324
CTDI = 13.33 mGy
14% dose savings and improved contrast!
Detector Efficiency
Geometric Efficiency
Detector Type
Detector Arrangement
Extremely sensitive, ceramic, scintillators.
Closely packed, minimal interspace material
GE Gemstone - Discovery HD
Ultrafast Ceramic Detector (UFC) - Siemens
Iterative Reconstruction Techniques
A return to an older CT reconstruction method.
Departure from the filtered-back projection.
Series of "educated guesses" to arrive at an image with acceptable signal-to-noise.
Results in significant dose reduction!
Siemens : IRIS & SAFIRE
Phillips: iDose
Toshiba: ADIR
Iterative Reconstruction
Dual Energy CT
Kaza RK, (2012) Dual-Energy CT with Single- and Dual-Source Scanners: Current Applications in Evaluating the Genitourinary Tract. RadioGraphics, 32, 353-369. Mayo Foundation for Medical Education and Research, 2010
either single- or dual-source (one x-ray tube or two)
single-source uses fast kilovoltage switching
post-contrast and "virtual" unenhanced images in a single acquisition
GE & Phillips
Contrast-enhanced, nephrogenic phase
Virtual unenhanced from material decomposition algorithm
Eliminate an entire acquisition phase = dose savings!
Reduce mAs to highest tolerable noise level.
The new buzzword
Similar to ALARA
Be aggressive in mAs reduction on follow-up exams!
Kalra MK. (2004) Strategies for CT Radiation Dose Optimization, Radiology, 230, 619-628.
McCollough CH, (2012) The use of bismuth shields for CT should be discouraged. Medical Physics, Vol. 39, No. 5.
5 year periods
Peak? ----->
Consumer Reports - March, 2015
Wall Street Journal - 2012
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