→Radiation exposure from a fixed CT parameters results in relatively higher ...
CT scans are used with regularity in the initial evaluation of the pediatric trauma ...
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 • • •
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 •
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 • • • • • • • •
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 •
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 • • • •
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 •
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
