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NC HPS Meeting 10/18-19/2001 Boone, NC
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Transcript of NC HPS Meeting 10/18-19/2001 Boone, NC
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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
NC HPS MeetingNC HPS Meeting10/18-19/200110/18-19/2001Boone, NCBoone, NC
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Measurement of Effective Dose Equivalent Measurement of Effective Dose Equivalent Using a Newborn PhantomUsing a Newborn Phantom
Topics1. Why pediatric CT dosimetry?2. Scope of study3. Materials and Methods4. Results5. Conclusions
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Why pediatric CT dosimetry?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 Don’t 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 2001:176;303-306American Journal of Roentgenology 2001:176;303-306
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2. Scope of study2. 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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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.
3. Materials and Methods3. Materials and Methods
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Brief description of phantomBrief 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 phantomBrief description of phantom
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Dosimeter distributionDosimeter 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 ProtocolNewborn Abdomen CT ProtocolDose Comparison: CT/i vs QX/i Dose Comparison: CT/i vs QX/i
CTII. High3 mm, pitch 1.0140 kVp;120 mA, 0.8 sec
II. Medium5 mm, pitch 1.5140 kVp; 90 mA; 0.8 sec
III. Low5 mm, pitch 2.0120 kVp; 70 mA; 0.8 sec
QXII. High 2.5/7.5 HQ140 kVp; 100 mA, 0.8 sec
II. Medium3.75/11.25 HQ140 kVp; 70 mA, 0.8 sec
III. Low5.0/22.5 HS120 kVp; 60 mA, 0.5 sec
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Calculation of Effective Dose EquivalentCalculation of Effective Dose Equivalent
ICRP Report No. 26 (1977)Effective Dose Equivalent = T WT HTWhere WT = weighting factor; HT = dose equivalent.
Selected Organs (Newborn Phantom – CIRS, Norfolk, VA) –see Chart (Rt).
Organs Slice #Thyroid 6
BM/Mandible 5
BM/Femor 14
Testes 14
BM/Pelvis 12
Intestine 12
Ovaries 12
Kidney 11
Intestine 11
Liver 10
Stomach 10
Lungs 9
BM/Spine 9
BM/Rib 8
Lungs 7
BM/Spine 7
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Effective Dose EquivalentNewborn Phantom
QXI vs CTI
High Medium Low0.0
0.5
1.0
1.5
2.0
2.5
3.0QXICTI2.3
1.51.3
0.82
0.35 0.32
Abdomen Scan Protocol
Effe
ctiv
e Do
seEq
uiva
lent
(mSv
)
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Newborn Newborn Chest CTChest CT Protocol ProtocolDose Comparison: CT/i vs QX/i plusDose Comparison: CT/i vs QX/i plus
CTII. High
3 mm, pitch 1.0140 kVp;100 mA, 0.8 sec
II. Low5 mm, pitch 2.0120 kVp; 50 mA; 0.8 sec
QXI PlusI. High
2.5/7.5 HQ, 140 kVp, 80 mA, 0.8 sec
II. Med3.75/1.25 HQ, 140 kVp, 50 mA, 0.8 sec
III. Low5.0/22.5 HS120 kVp; 40 mA, 0.5 sec
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Calculation of Effective Dose EquivalentCalculation of Effective Dose Equivalent ICRP Report No. 26 (1977)
Effective Dose Equivalent = T WT HT
Where WT = weighting factor; HT = dose equivalent.
Selected Organs (Newborn Phantom – CIRS, Norfolk, VA) –see Chart (Rt).
Organs Slice #BM/Mandible 5Thyroid 6Lungs 7BM/Spine 7BM/Rib 8Lungs 9BM/Spine 9Liver 10Stomach 10kidney 11Intestine Upper 11Ovaries 12BM/Pelvis 12Testes 14BM/Femor 14BM/ UPPER ARM ARMBM/ LOWER ARM ARMBM/RADIUS+ULNA ARM
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EDE (female)
Effective Dose Equivalent(Chest)
Newborn PhantomQXI (plus) vs CTI
High Med Low0.0
0.2
0.4
0.6
0.8QXICTI
0.70
0.11
0.59
0.075
0.40
Chest Scan Protocol
Effe
ctiv
e Do
seEq
uiva
lent
(mSv
)
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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).
5. Conclusions5. Conclusions