Radiation protection in pediatric CT

Transcription

1 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

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5 Background 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 x- rays is upto 47-59%

6 Background 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

7 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

8 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

9 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

10 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

11 From January 1999 to October 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

12 Factors contributing to unnecessary CT exams Overcautious ordering Time saving since immediate result is possible Lack of alternative examination modality such as US, MRI on emergency setting Appropriateness Criteria or Guidelines may not be enough to change practice

13 Justification 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

14 Optimization: CT 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

15 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

16 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 : kvp children or smaller adult : kvp Child-sizing a CT scan technique should not be limited to small children, should include adolescent Most pediatric patients imaged at pitch of in association with a rapid gantry rotation (>0.6s) to minimize scan time

17 Optimization: dose reduction technique provided by vendors 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

18 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:

19 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:

20 Shielding 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 AJR 2005; 184:

21 Diagnostic Reference Level (DRL) 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

22 EC DRL for pediatric CT 1996

23 DRL from 2006 UK national survey

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25 DRL NCRP 2012

26 Table 29. Korean DRL for Pediatric CT Head Chest Abdomen Age Neonate (0 ~ 1 month) CTDIvol (mgy) DLP (mgy*cm) month ~ 1 y ~ 5 y ~ 10 y Neonate (0 ~ 1 month) month ~ 1 y ~ 5 y ~ 10 y Neonate (0 ~ 1 month) month ~ 1 y ~ 5 y ~ 10 y 8 240

27 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

28 Low dose brain CT indications 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, 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: , April 2008

29 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

30 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 mAs) * 90% of pediatric emergency room CT scans are performed in adult-focused hospitals JACR 2011;8: Kanal et al

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34 Range of CTDI in ped CT in Korea (2012) Table 17. CTDI from phantom scan of pediatric CT (maximum/minimum) Age minimum CTDIvol (mgy) maximum maximum/ minimum Neonate Head (n=98) <1 y ~ 5 y Chest (n=50) Abdomen (n=55) 6 ~ 10 y ~ 5 y ~ 5 y *n : Number of Hospital *CTDI from 16cm phantom

35 CT Dose indices CTDIvol dose not represent patient dose CTDIvol is independent of changes in patient size Especially problematic in children

36 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

37 Displayed CTDIvol=18 Displayed CTDIvol=18 Displayed CTDIvol=18 AAPM 2011 Summit on CT Dose

38 Size Specific Dose Estimates (SSDE) 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

39 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

40 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

41 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

42 IAEA Poster: pediatric CT

43 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

44 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)

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46 6.6 Summary of principles for dose reduction in pediatric CT (Vock 2005) 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:

47 Summary 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

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