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

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

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

American Journal of Roentgenology 2001:176;303-306American Journal of Roentgenology 2001:176;303-306

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.

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

Brief description of phantomBrief description of phantom

Atom newborn phantom (Model 703-D) CIRS, Norfolk, VA

Cost: ~ $ 9K Joint effort between Duke

and CIRS

Brief description of phantomBrief description of phantom

Dosimeter distributionDosimeter distribution TLD locations in

organs pre-drilled Designed for TLD-

100 (3mm x 3 mm x 1 mm)

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

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

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

)

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

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

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

)

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