Measurement of Effective Dose Equivalent Using a Newborn Phantom

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NC HPS Meeting10/18-19/2001Boone, NC

• Measurement of Effective Dose Equivalent Using a
  Newborn Phantom
• L. Barnes 1, T. Yoshizumi 1,2, D. Frush 2, V.
• Varchena3, M. Sarder 1, E. Paulson 2
• 1 Radiation Safety Office, 2 Department of
  Radiology,
• 3Computerized Imaging Reference Systems, Inc.
• Duke University Medical Center
• Durham, NC

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Measurement of Effective Dose Equivalent Using a
Newborn Phantom

• Topics
• Why pediatric CT dosimetry?
• Scope of study
• Materials and Methods
• Results
• Conclusions

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Why pediatric CT dosimetry?

• Only 40 of CT users adjust techniques for
  patient size (preliminary NEXT data)
• NEXT Committee on Nationwide Evaluation of X-ray
  Trend, CRCPD
• Dont have organ dose data in multi-detector CT
  scanners (your guess is as good as mine)
• Dose indices such as CTDI and the dose-length
  product do not represent actual organ dose and
  are of limited value in risk assessment
• Problems created by news media frenzy in recent
  months

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American Journal of Roentgenology
2001176303-306
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2. Scope of study

• Measure Effective Dose Equivalent using single
  and multi-detector CT scanners for chest and
  abdomen CT protocols
• Two protocols were selected Chest and Abdomen
• Scan parameters (kVp, mA, sec, pitch, etc.) were
  selected to represent High, Medium, and Low
  techniques.

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3. Materials and Methods

• Dosimeters
• Harshaw TLD-100
• Harshaw auto TLD reader QS 5500
• CT scanners
• GE QXi (multi-detector) and CTi (single
  detector)
• Anthropomorphic phantom
• Newborn phantom, CIRS, Inc., Norfolk, VA.

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Brief description of phantom

• Atom newborn phantom (Model 703-D)
• CIRS, Norfolk, VA
• Cost 9K
• Joint effort between Duke and CIRS

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Brief description of phantom
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Dosimeter distribution

• TLD locations in organs pre-drilled
• Designed for TLD-100 (3mm x 3 mm x 1 mm)

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Newborn Abdomen CT ProtocolDose Comparison CT/i
vs QX/i

• CTI
• High
• 3 mm, pitch 1.0
• 140 kVp120 mA, 0.8 sec
• Medium
• 5 mm, pitch 1.5
• 140 kVp 90 mA 0.8 sec
• Low
• 5 mm, pitch 2.0
• 120 kVp 70 mA 0.8 sec

• QXI
• High
• 2.5/7.5 HQ
• 140 kVp 100 mA, 0.8 sec
• Medium
• 3.75/11.25 HQ
• 140 kVp 70 mA, 0.8 sec
• Low
• 5.0/22.5 HS
• 120 kVp 60 mA, 0.5 sec

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Calculation of Effective Dose Equivalent

• ICRP Report No. 26 (1977)
• Effective Dose Equivalent ST WT HT
• Where WT weighting factor
• HT dose equivalent.
• Selected Organs (Newborn Phantom CIRS, Norfolk,
  VA) see Chart (Rt).

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Newborn Chest CT ProtocolDose Comparison CT/i
vs QX/i plus

• CTI
• High
• 3 mm, pitch 1.0
• 140 kVp100 mA, 0.8 sec
• Low
• 5 mm, pitch 2.0
• 120 kVp 50 mA 0.8 sec

• QXI Plus
• High
• 2.5/7.5 HQ, 140 kVp, 80 mA, 0.8 sec
• Med
• 3.75/1.25 HQ, 140 kVp, 50 mA, 0.8 sec
• Low
• 5.0/22.5 HS
• 120 kVp 40 mA, 0.5 sec

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Calculation of Effective Dose Equivalent

• ICRP Report No. 26 (1977)
• Effective Dose Equivalent ST WT HT
• Where WT weighting factor
• HT dose equivalent.
• Selected Organs (Newborn Phantom CIRS, Norfolk,
  VA) see Chart (Rt).

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EDE (female)
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5. Conclusions

• For abdomen protocol, the effective dose
  equivalent between high and low scan techniques
  differed a factor of 7 for QXi and that of 5 for
  CTi.
• For chest protocol, the effective dose equivalent
  between high and low scan techniques differed a
  factor of 6 for QXi and 8 for CTi.
• It is important to adjust scan techniques for
  the size and weight of a patient.
• A multi-detector scanner (QXi) resulted in
  substantially higher dose than a single-detector
  scanner (CTi).