Download Radiation Safety in Pediatric Imaging - RPOP

Radiation protection in
pediatric CT
Whal Lee, MD, PhD, Associate Professor
Seoul National University College of Medicine
Seoul National University Hospital, Department of Radiology
Ah Young Jung, MD, PhD, Assistant Professor,
Hallym University Kangnam Sacred Heart Hospital,
Department of Radiology
Kyung Hyun Do, MD, PhD, Associate Professor
University of Ulsan College of Medicine
Asan Medical Center, Department of Radiology
Background
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Increasing number of examinations with radiation
exposure
Advance in CT technology with rapid expansion of CT
utilization
Annually 3.6 billion diagnostic and medical and dental
examination involving radiation performed worldwide
CT contribution to collective dose due to medical xrays is upto 47-59%
Background
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NCRP report 2009 estimates, 8-10% of CT
examinations in the USA performed on children
The growth in CT utilization is higher in the pediatric
than adult population in US
Particularly pronounced rise in adolescents undergoing
chest CT in the emergency department setting for
suspected pulmonary embolism or Trauma
Growing incidence of CT
• New indications for CT with advent of
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MDCT
Overcautious ordering related to
medico-legal problem
Financial incentive system
High technology exam wanted by public
Special considerations in children
• Children more sensitive with factor of 3–5
relative to adults
• Children have more years ahead in which
cancerous changes might occur
• Girls are more at risk than boys
• Radiologist tend to demand less noisy image
in small patients
• Small children have less adipose tissue
Special considerations in children
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About 33-50% of the pediatric CT examinations have
questionable indications
• Lack of size-based adjustments in technique
Radiation exposure from a fixed CT parameters results
in relatively higher dose for a child's smaller crosssectional area compared with an adult
• Many exams are still conducted using inappropriate
technical factors
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6-year period, ED patients, ages 0 to 17 years
Pediatric ED patient volume increased by 2%
Distribution of triage acuity remained relatively stable
Head CT increased 23%, Cervical spine CT 366%, Chest CT 435%, Abdominal CT
49%, miscellaneous CT 96%
Most pronounced in adolescents ages 13 to 17 years
Increased vehicular blunt trauma
Emergency physician believing radiation risk restricted to youngest children with
less concern for adolescents
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From January 1999 to October 2003
1653 children with traumatic injuries evaluated by trauma team
1422 patients undergoing 2361 CT scans
54% of scans were interpreted normal
897 with abdominal CT scan – only 2% exploratory laparotomy
CT scans are used with regularity in the initial evaluation of the
pediatric trauma patient, and perhaps abdominal CT imaging is
being used too frequently
Factors contributing to unnecessary
CT exams
• Overcautious ordering
• Time saving since immediate result is possible
• Lack of alternative examination modality such
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as US, MRI on emergency setting
Appropriateness Criteria or Guidelines may not
be enough to change practice
Justification
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Is this appropriate study?
Do not perform the study if not indicated
Consider other modality: US, MRI
Communications with a department of clinical
radiology
The American College of Radiology “Appropriateness
Criteria”
The European Commission guidelines and United
Kingdom's Royal College of Radiologists “ Referral
guidelines for imaging”
Optimization: CT
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Child-friendly environment
Indication based imaging
: choose a specific exam protocol which addresses the clinical
question while minimizing dose
: Low dose protocol for shunt FU brain CT, funnel chest CT,
extremity CT
Patient positioning : Center the patient in the gantry
Single-phase imaging: Minimize multiple scan (pre, delay..) one
phase is usually enough for children
Limit coverage to answer clinical questions, especially when
examining multiple area
Optimization: CT
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Reduce dose during scout views, PA projection>AP
Obtain topography before shield
Shields
Minimize radiation dose for bolus tracking
Angulations of the gantry for head CT studies can reduce the eye
dose by 90%, to about 3–4mGy
Better reconstruction algorithms
Calculate radiation dose
Report radiation dose : dose display
Optimization: adjusting CT parameters
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Adjust CT technique : individual setting based on indication, body region,
body size
• Tube current (mA) directly, linear relationship
ex) 50% reduction in tube current 1/2 dose
• Peak kilovoltage (kVp) : direct, non linear relationship
standard adult : 120-140 kVp
children or smaller adult : 80-120 kVp
• Child-sizing a CT scan technique should not be limited to small children ,
should include adolescent
• Most pediatric patients imaged at pitch of 1.3-1.4 in association with a
rapid gantry rotation (>0.6s) to minimize scan time
Optimization: dose reduction technique
provided by vendors
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Automatic exposure control (AEC)
Real time mAs modulation
reference mAs vs. noise index
Adaptive dose shielding
active z-axis collimation to reduce overscanning
Automated organ based current modulation
reduce dose to sensitive tissues such as breast
Iterative reconstruction ex)VEO, ADIR, iDOSE, IRIS
projection based noise reduction algorithm
Automated tube voltage
Ten steps to lower CT radiation dose for
patients while maintaining image quality
1. Increased awareness and understanding of CT
radiation dose issues among radiologic technologists
2. Enlist the services of a qualified medical physicist
3. Obtain accreditation from the ACR for your CT
program
4. When appropriate, use an alternative imaging
strategy that dose not use ionization radiation
5. Determine if the ordered CT is justified by the clinical
indication
AJR 2010; 194:868-873
Ten steps to lower CT radiation dose for
patients while maintaining image quality
6. Establish baseline radiation dose for adult sized
patients
7. Establish radiation doses for pediatric patients by
‘Child-sizing’ CT scanner parameters
8. Optimize pediatric examination parameters
9. Scan only the indicated area: scan once
10. Prepare a child friendly and expeditious CT
environment
AJR 2010; 194:868-873
Shielding
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Protective shielding
• Gonads should be protected when within or close
(near than 5cm) to the primary beam
• Properly adjusted gonadal capsule reduce absorbed
testes dose upto 95%
Eye shielding
Breast , thyroid shield
EUR 16261
AJR 2005; 184:128-130
Diagnostic Reference Level (DRL)
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ICRP recommends the use of DRL for patients
DRL is used in medical imaging to indicate whether,
the patient dose from a specific procedure is unusually
high or low for that procedure
Reference levels are typically set at the 75th percentile
of the dose distribution from a survey conducted
The use of DRL has been shown to reduce the overall
dose and the range of doses observed in clinical
practice
EC DRL for pediatric CT 1996
DRL from 2006 UK national survey
DRL NCRP 2012
Table 29. Korean DRL for Pediatric CT
Head
Chest
Abdomen
Age
CTDIvol (mGy)
DLP
(mGy*cm)
Neonate
(0 ~ 1 month)
16
210
1 month ~ 1 y
20
260
2~5y
28
370
6 ~ 10 y
36
500
Neonate
(0 ~ 1 month)
2
25
1 month ~ 1 y
3
45
2~5y
5
100
6 ~ 10 y
6
120
Neonate
(0 ~ 1 month)
2
50
1 month ~ 1 y
3
80
2~5y
6
180
6 ~ 10 y
8
240
Iterative Reconstruction
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VEO, ASIR, Adaptive statistical iterative reconstruction : GE
IRIS, Iterative reconstruction in image space : Siemens
AIDR, Adaptive iterative dose reduction : Toshiba
iDose : Philips
Image from web site www.siemens.com
Low dose brain CT indications
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Craniosynostosis
(80 kVp and 50 mAs)
Shunt FU CTs
(80 mAs: 15.5 mGy, 0.58 mSv)
dose can be submilisievert
Multiple follow up or repeat CTs for malformations,
tumors, trauma, cerebrovascular disease
(80 kVp, 90-140 mA)
Low-Dose Nonenhanced Head CT Protocol for Follow-Up Evaluation
of Children with VP Shunt: Reduction of Radiation and Effect on Image Quality
AJNR 29:802-806, April 2008
80kVp CTA for child
M /19 month, 10kg, Arterial switch op
CTDI = 0.28~0.6 mGy
DLP = 7 mGy/cm
Effective dose = 0.13~0.5 mSV
Variation in pediatric head CT
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Web-based questionnaire to 77 trauma centers in
Washington state ( 8 pediatric designated center)
• More than 10 fold variation in estimated median
effective dose, within and between trauma centers
• Pediatric designated centers had significantly lower
mAs( 87.4 vs. 182.5mAs)
* 90% of pediatric emergency room CT scans are
performed in adult-focused hospitals
JACR 2011;8:242-250 Kanal et al
Range of CTDI in ped CT in Korea (2012)
Table 17. CTDI from phantom scan of pediatric CT (maximum/minimum)
Age
Head
(n=98)
Chest
(n=50)
Abdomen
(n=55)
CTDIvol (mGy)
minimum
maximum
maximum/
minimum
Neonate
2.5
52.1
20.5
<1 y
1.9
52.1
27.8
2~5y
5.3
71.1
13.4
6 ~ 10 y
9.2
71.1
7.7
2~5y
1.1
7.9
7.3
2~5y
1.0
10.1
10.0
*n : Number of Hospital
*CTDI from 16cm phantom
CT Dose indices
• CTDIvol dose not represent patient dose
• CTDIvol is independent of changes in patient
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size
Especially problematic in children
Displayed
CTDIvol=18
Displayed
CTDIvol=18
Displayed
CTDIvol=18
Dose measurements at surface and the center of 10cm, 16cm, 32cm phantom with
120 kVp, 200mAs, pitch 1, 1cm fan beam width and same bowtie filter
radiation dose to newborn abdomen (10cm) will be 2.6 time greater than adult
(47 mGy vs. 18 mGy). However the displayed CTDIvol will be 18mGy for all
Displayed
CTDIvol=18
Displayed
CTDIvol=18
Displayed
CTDIvol=18
AAPM 2011 Summit on CT Dose
Size Specific Dose Estimates (SSDE)
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Correction factor developed by AAPM Task Group 204
to better estimate patient dose during CT scan
SSDE (product of correction factor and CTDIvol)
estimates the peak dose at the center of the scan
length of the irradiated patient
Accuracy of SSDE within 20%
First prototype pediatric registry, the Quality
Improvement Registry in CT Scans in Children
(QuIRCC) is already using SSDE in dose recording
Ex) Displayed CTDIvol 5.4mGy (using 32cm) /10.8mGy (using 16cm )
SSDE (if 32cm phantom used )= 5.4 mGy x 2.5=13mGy
SSDE (if 16cm phantom used) = 10.8 mGy x 1.24=13
PA dimension of 9.9 cm LAT
dimension of 12.3 cm
:LAT+PA dimension 22.2cm
Improvement through awareness
Peak kilovoltage used by members of the Society for Pediatric Radiology for pediatric
chest (a) and abdomen (b) MDCT from a 2006 survey compared with a 2001 survey
Improvement through awareness
Mean tube current used by members of the Society for Pediatric Radiology for
pediatric chest (a) and abdomen (b) MDCT over several age ranges from a 2006
survey compared with a 2001 survey
IAEA Poster: pediatric CT
10 Pearls: Radiation protection of patients in CT
1. Perform scan only if it is indicated!
2. Encourage use of alternative non-ionizing imaging
(MRI,US)
3. Always check if patient may be pregnant
4. Start using images with some noise without loss of
diagnostic information
5. Use indication-specific CT protocols for each body
region
10 Pearls: Radiation protection of patients in CT
6. Multiple phase CT should NOT be performed
routinely
7. Adjust exposure parameters according to patient
and body part
8. Know your equipment: ex) AEC
9. Good technique: Lower kVp, mAs…
10. Pay attention to radiation dose values and
compare with diagnostic reference levels (DRLs)
6.6 Summary of principles for dose reduction
in pediatric CT (Vock 2005)
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Rigorous justification of CT studies.
Prepare the patient.
Accept image noise as long as the scan is diagnostic:
Optimize scan parameters:
Limit scan coverage:
Avoid non-justified multiple scans of the same area:
Summary
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Radiologist is the gatekeeper in the process of
justification
Be aware of unique consideration for children
Perform only necessary CT : communication with
radiologist
Adjust exposure parameters for CT
Increased awareness through education : radiologist,
clinician, technologists, patient
Future development of evidence based practice
strategies for pediatric ER patients