Review of Recent CT Accidents:
Dosimetry, Risk Analysis, and Lessons Learned
NC HPS SPRING MEETING
MARCH 4-5, 2010
RALEIGH, NC
Terry Yoshizumi, PhD*, David Enterline, MD
Greta Toncheva, MS
Duke University Medical Center
Durham, NC
1
ACKNOWLEDGEMENTS
•
•
•
•
Robert Reiman, MD
Don Frush, MD
Ehsan Samei, PhD
James Colsher, PhD
2
TOPICS
1.
2.
3.
4.
5.
6.
7.
8.
9.
Review of recent CT accidents
What is CT perfusion (CTP)?
Why is the dose so large?
How do we measure organ doses?
Results of Cedars-Sinai’s protocols
Risks identified
Scrutiny began at federal level
Lessons learned
Concluding remarks
3
Review of Recent CT Accidents
2005
Eur Radiol (2005)
15:41-46
Hair loss: 3 cases
CTP + angiography
study
2008
2 1/2 yr old
151 scans in period of 65
minutes
(CBS13.com)
2009
FDA Warning 10-8-09
Cedars-Sinai, CTP
206 pts over 18-mo.
3-4 Gy (normal 0.5 Gy)
80 hair loss
56 direct exposure to lens
of the eye
+ 50 identified
from other states
(FDA Report)
4
Brain CT Perfusion Imaging
Clinical Applications
•
•
•
•
Stroke and Ischemia
Diamox Challenge
Vasospasm
Tumor evaluation
– CTP and CT
permeability
Tracer Kinetic Theory
Analysis of time-concentration curves
0.14
0.12
0.10
Volume = Area under
concentration
curve
0.08
0.06
Area
0.04
0.02
0.0
-0.02
0.14
0.12
Volume
Flow =
Mean transit time
0.10
0.08
0.06
0.04
0.02
0.0
-0.02
MTT
Perfusion Imaging
• CT: Conc = k (density)
CBV
0.14
0.12
0.10
0.08
CBF
0.06
0.04
0.02
0.0
-0.02
Time Concentration Curve
MTT
Choosing Arterial Input Funct (AIF) & Venous Output F (VOF)
VOF
AIF
Compensated ischemia of LICA
Increased CBV
(green) due to
autoregulation
Prolonged MTT (red)
MTT
Low CBF (blue)
CBF
CBV
Compensated ischemia of LICA
MTT
Normal: 3-5 sec
CBF
> 40 mL/min/100 g brain
CBV
~3
Borderline CBF With Low CBV Predicts
Infarction (No Intervention)
infarct
CBV - 5 hours
T2WI - 24 hours
CT Perfusion- Absolute and
Relative CBF Analysis
• Absolute CBF of 10-20 ml/100g/min
represents ischemic tissue but viability
depends on duration of ischemia
• When ischemia is associated with an area of
core infarct, this represents the penumbra
• Decreased CBV with compromised CBF
implies infarction
CT Perfusion
•
•
•
•
CINE mode:
80 kVp, 200 mA, 1 sec
Repeat 45 sec
Table fixed
13
WHEN THE DOSE BECOMES AN ISSUE IN CTP
When human errors introduced
– scan parameters altered, i.e., the energy changed from
80 kVp to 120 kVp, or tube current (mA) modulation used
without understanding consequences
Why:
Display constantly updated images by continuous
rotation of the tube at the same location; potential for
high dose at the level of scan
14
How do we measure organ doses?
A. Manual Look-up tables (Outdated)
B. Organ dose from CTDI (No value, but CTDI is
useful for monitoring dose)
C. Monte Carlo based dose calculator (complex,
time consuming)
D. Effective Dose from DLP (No value)
E. Anthropomorphic phantom with TLDs
(Labor intensive)
F. Anthropomorphic phantom with
MOSFET(metal oxide semiconductor field
effect transistor) detectors (Best value)
15
Materials and Methods
• Patient
Dose Verification System
AutoSense, Model TN-RD-60
•Radiation detectors:
20 Metal Oxide Field Effect
Semiconductor Transistors (MOSFET),
Model TN-1002RD, High sensitivity
Reader, Model TN-RD-15
Bias supply, Model TN-RD -22
AutoSense PC Software, TN-RD-45
•MOSFET dosimeter:
Silicon chip 1mm2
Active area 0.2mm x 0.2mm
MOSFET AUTO-SENSE SYSTEM
MOSFET
16
Adult Male Phantom
Tissue Equivalent
Anthropomorphic Phantom
Model 701-D
Steven
SN : 701-285
39 slabs
Height -173 cm, Weight - 73 kg
Thorax Dimensions: 23 x 32 cm
Head: AP 21cm, Lateral 17.1cm
Neck at the thyroid: AP 13 cm, Lateral 14.6 cm
CIRS
www.cirsinc.com
A FEW WORDS ABOUT THE ED AND WEIGHTING
FACTORS
18
CONCEPT OF EFFECTIVE DOSE EQUIVALENT OR EFFECTIVE DOSE
ICRP Report 26 (1977)
Dose Equivalent
Quality Factor
Weighting Factor
Effective Dose Equivalent

1-12-10
ICRP Report 60 (1990)
Equivalent Dose
Radiation Weighting Factor
Tissue Weighting Factor
Effective Dose

•ICRP 103 (2007)
•Equivalent Dose
•Radiation Weighting Factor
•Tissue Weighting Factor
•Effective Dose
19
WT : ICRP 26 (1976), ICRP 60 (1990), ICRP 103 (2007)
ORGAN
ICRP26
(1977)
ICRP60
(1990)
ICRP 103
(2007)
Gonads
0.25
0.20
0.05
Bone marrow
0.12
0.12
0.12
Lung
0.12
0.12
0.12
Stomach
0.12
0.12
Colon
0.12
0.12
0.05
0.12
Bladder
0.05
0.05
Liver
0.05
0.05
Esophagus
0.05
0.05
Breast
Thyroid
0.03
0.05
0.05
Skin
0.01
0.01
0.01
Bone surface
0.03
0.01
0.01
Kidneys
0.01
Brain
0.01
Salivary glands
0.01
Remainder tissues
1-12-10
0.15
0.30
0.05
0.10
20
ICRP 103 Weighting Factors
Organ
ICRP 103
Remainder
ICRP 103
Gonads
0.08
Adrenals
0.0086
Bone marrow (red)
0.12
Extra-thoracic tissue
0.0086
Lung
0.12
Gall bladder
0.0086
Breast
0.12
Heart wall
0.0086
Thyroid
0.04
Kidneys
0.0086
Bone surface
0.01
Lymph nodes
0.0086
Colon
0.12
Muscle
0.0086
Stomach
0.12
Oral mucosa
0.0086
Bladder
0.04
Pancreas
0.0086
Liver
0.04
Prostate
0.0086
Esophagus
Skin
Salivary glands
0.04
0.01
0.01
Small intestine
0.0086
Brain
Remainder
Total
0.01
0.12
1
Spleen
Thymus
Uterus / cervix
0.0086
0.0086
0.0086
Total
0.12
21
Notes on Effective Dose Calculations
• Skin Dose: taken the highest of the anterior and posterior,
%
the posterior skin dose is reduced due to attenuation by
Distributio
the table
Red marrow
n
• Brain Dose: the dose is averaged from the dose of all
SKull
brain locations
(cranium +
• Bone marrow: the dose is a sum of the measured bone
8.32
facial)
marrow dose at different locations multiplied by the %
28.5
Scapulae
distribution
0.79
Clavicles
• Lens of the eye: average of the two
Ribs
19
• Bone surface: the measured dose is adjusted with the dry
bone f-factor (different for soft tissue and bone), f-factor is Spine (upper
portion)
2.66
the conversion from R to cGy, at different tissues and
Spine (middle
energies used during the MOSFET calibrations
portion)
17
• All protocols were measured three times and the
averaged value was used
• Misc.: in occasions where out of three measurements two
are “0”, only the one number was used, or if there was one
“0” and two numbers, the average of the only two was
used
• The new ICRP 103 was used with the new weight factors
22
(listed in the next slide)
ADULT CTP
Scan #
Protocol
2
Adult
Perfusion
Adult
Perfusion
3
Adult
Perfusion
Auto mA
1
FDA 0.5 Gy
Images Scan type
Table speed
(mm/rot)
kV
mA
Total
Exposur
e time
(sec)
1-360
CINE Full
Axial
5.0 8i 1sec
80
200
45
531.43
2125.71
40 mm
1-360
CINE Full
5.0 8i 1sec
120
200
45
1714.29
6857.13
40 mm
120
min 100 max
520
NI=2.4
45
4457.14
17828.55
1-360
CINE Full
5.0 8i 1sec
CTDIvol
(mGy)
Detector
DLP (mGy*cm) coverage
23
TUBE CURRENT MODULATION
Basic Concept:
 Adjust the tube current to accommodate
the patient contour and composition
24
TUBE CURRENT MODULATION
mA1
mA2
mA1
mA2
modulation around the z-axis
mA1
modulation around the cross-section
mA2
modulation – axial and helical
25
How smart mA works
• Projection data from a scout scan measures the
patient and determines how to modulate the mA for
improve dose efficiency and consistent IQ
100%
Fixed mA
55%
Z Modulation - Auto mA
40% XYZ Modulation
mAs
300
250
200
150
100
50
0
0.0
CHEST 100.0
200.0
ABDOMEN
300.0
400.0
PELVIS
500.0
26
Jim Colsher, GE Healthcare
An AutomA Example
(Noise Index =24)
sd 25.4
sd 23.7
sd 22.6
GE Healthcare
27
Results: Effective Dose
ED (Adult), excerpt from
NCRP 160, 2009
ADULT CTP
Effective Dose for 45 sec Scan
120.0
100.2
ED (mSv)
100.0
Head
0.9 - 4
Chest
4 – 18
AbdomenPelvis
3 - 25
1 – 10
12.0
Angiography:
head
5 - 32
80 kVp 200 mA
Angiography:
heart
80.0
60.0
35.0
40.0
20.0
ED per scan
(mSv)
0.0
120 kVp 200 mA
120 kVp Auto mA
max 520 mA
28
Results: Organ doses
ADULT CTP
Organ Doses for 45 sec Scan
Organ Dose (mGy)
3500.0
3000.0
2500.0
80 kVp 200 mA
120 kVp 200 mA
2000.0
1500.0
120 kVp Auto mA
mA
max 520
1000.0
500.0
0.0
29
Results: Lens of the Eye
ADULT CTP
Lens of the Eye Dose
600.0
Organ Dose (mGy)
500.0
434.6
400.0
300.0
176.9
200.0
100.0
38.5
0.0
80 kVp 200 mA
120 kVp 200 mA
120 kVp Auto mA
max 520 mA
30
Results: Skin Dose
ADULT CTP
Skin Dose for 45 sec Scan
3500.0
3,061
Organ Dose (mGy)
3000.0
2,451
2500.0
2000.0
Anterior
1500.0
Posterior
1000.0
500.0
458
231
398 318
0.0
80 kVp 200 mA 120 kVp 200 mA 120 kVp Auto mA
max 520 mA
31
Brain Dose
GE Adult Brain Perfusion CT
Brain Dose at Different Locations
Organ Dose (mGy)
3500.0
2,916
3000.0
2500.0
2,221
1,967
2000.0
2,192
Location 1
1500.0
Location 2
1000.0
Location 3
500.0
284 244 225 257
357
233 282
288
Location 4
0.0
80 kVp 200 mA 120 kVp 200 120 kVp Auto
mA
mA
max 520
mA
32
Risks identified from CTP
Threshold dose (Gy)
Clinical CT dose (Gy)
FDA: 0.5 Gy
Temporary Epilation
3 Gy (FDA)
Quite possible
Main Erythema
6 Gy (FDA)
Unlikely, but possible
15-20 Gy (FDA)
Unlikely, but possible
Moist desquamation,
dermal necrosis,
secondary ulceration
Cataracts
•2-5 Gy (acute or a
few fractions)
•0.6-0.8 Gy (chronic
exposure to diag. xrays over yrs, or
involve radiations
other than photons
(Reiman)
Possible for both
acute and lower
threshold
33
FDA Report (10-7-09)
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/Detail.CFM?M
DRFOI__ID=1495886 (GE Version)
SUMMARY:
• No malfunction on the scanner
• Protocol altered by the site user
34
Recommendations from FDA
• Check for excess radiation from CT Perfusion
• Review radiation dosing protocols for all CT perfusion
studies
• Implement quality control procedures
• Check the CT scanner display panel before performing a
study to make sure the amount of radiation to be
delivered is at the appropriate level for the individual
patient.
• For multiple scans on a patient during one imaging
session, practitioners should adjust the dose of radiation
35
Lessons learned
• Need for quality assurance of protocol
development/modification including dosimetry
oversight
• Need for team approach in dealing with patient
safety
• Need for radiation safety education for all
personnel involved
• Need for institutional oversight by the Radiation
Safety Committee
36
Concluding remarks
Key questions to ask regarding CedarsSinai incident?
1. Was it machine failure?
2. Was it human failure?


Wrong scan protocols implemented – no one
challenged changing 80 kVp to 120 kVp, or use of
Auto mA mode with low noise factor
Failure by the technologists, radiologists and physicist
3. What signs were there?

High CTDI values missed. You must look for it!
4. What was the protocol review process?
37
Concluding Remarks
CONGRESSIONAL HEARING OCCURRED (F-2-26-2010). This may
be the beginning of a new period for radiation protection.
38
Concluding remarks
WHAT WAS LOST IN ALL THESE HYPE?
• Cold Facts on Stroke
– The third leading cause of death in the US
– The leading cause of adult disability
– Every year about 750,000 Americans experience stroke and about 160,000
(21%) die from it
• Fundamental issue: Over-radiation without oversight
–
CTP is a valid protocol that uses 0.5-0.8 Gy , but should be < 1Gy
Live/die vs. Hair Loss
WHICH WOULD YOU CHOOSE?
39
THANK YOU.
40