A Monte Carlo Approa

External Dose Uncert

Timothy D Taulbee MS, CH

James W. Neton PhD, CHP

National Institute for Occupational Safety 

Office of Compensation Analysis and 
Overview Overview

 Elements of External Dose Rec

Elements of External Dose Rec

 Organ Dose Conversion Factors Organ Dose Conversion Factor Development of Organ Dose Un

Development of Organ Dose Un

using Monte Carlo Sampling using Monte Carlo Sampling
Dosimeter Dose

 Summation of dosimeter readin

Summation of dosimeter readin

given year given year

D

D= D1+D

2+D

3+...

D

n

 Uncertainty Uncertainty 

σD2 = 

σ12 + 

σ22 + 

σ32 + ...

σn

2

Mean = 8

Dosimete

0.00 2.00 4.00 6.00 

Frequency

0

200400600800

1000
Missed D

0.00 2.00 4.00 6.00 8

Frequency

0

200400600800

1000

Missed Dose Determin

 Critical Components

• Limit of Detection (LOD)• Number of zero recordings (n)

Upper nLOD

LOD Geometric Mean n

=

=

95%

2

G
Conversion to Organ D

Conversion to Organ 

 Primary Factor

• Target organ – primary cancer

 Additional factors effecting conv

• Monitoring device (Film or TLD)• Energy of emission• Exposure geometry
Monitoring Device Monitoring Device

Bone Marrow Lung Breast (Female

Dose Conversion Factor (DT/DM)

0.00.20.40.60.81.01.21.41.6

D

T/H

p(10) 

D

T/Exposure (R) 

100 keV – AP Geometry

Data from 
Energy Banding Energy Banding

DCF for Hp(10) to Lung Dose – AP Geo

Dat

Photon Energy (MeV)

0.01 0.1 1 

Dose Conversion Factor

Lung Dose (DT) / Hp(10)

0.00.20.40.60.81.01.2

0.870

0.082

0.695
Exposure Geometr

Exposure Geometr

Photon Energy (MeV)

0.01 0.1 1 

Dose Conversion Factor

Lung Dose (DT) / Hp(10)

0.00.20.40.60.81.01.2

Anterior-Posterior Posterior-Anterior Rotational GeomeIsotropic Geometr

Data fro
Likeliest Dose Conversio

Likeliest Dose Conversio

 Weighted approach based on job an

Weighted approach based on job an

interview interview

 Example: 90% AP geometry and 10% ROT Geo

0.6800.90

(

0.695

)

0.10

(

0.552

)

0.90

(

)

0.10

(

(10), , 

,30 250 

==

+

=

+ DCFW DCFH

p

Eγ − keV AP DCFH

(

)

(

)

() 

ROT

M ROT ISO

PA

M AP

M

W AP

w DCF

D ,E

w D

DCF

D ,E

w DCF

D ,E

w DC

γ

γ

γ

+

=

+
Photon Energy (MeV)

0.01 0.1 1 

Dose Conversion Factor

Lung Dose (D

T) / Hp(10)

0.00.20.40.60.81.01.2

Anterior-Posterior Posterior-Anterior Rotational GeomeIsotropic Geometr

Exposure Geometry Unc

Exposure Geometry Unc

Lower Limit = 0.127

Upp

0.680

30 -250 keV

Data fr
Dose Conversion Factor (

0.0 0.2 0.4 0.6 

Frequency

0

200400600800

DCF Triangular Distrib

DCF Triangular Distrib

Mode = 0.680

Lower Limit = 0.127 
Development of the Orga

Uncertainty Distribut

 Organ dose uncertainty is determine

Monte Carlo sampling from each of tcomponent distributions and the assconversion factor uncertainty.

 Recall

• Dosimeter Dose – Normal• Missed Dose – Lognormal• Dose Conversion Factor - Triangular
Uncertainty Distribut

Uncertainty Distribut

Dose Conversion Factor (DCF)

0.0 0.2 0.4 0.6 0.8 1.0

Frequency

0

200400600800

Dosimeter Dose (mSv)

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00

Frequency

0

200400600800

1000

Missed Dose (mSv)

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00

Frequency

0

200400600800

1000

××

==

Dose Conversion Factor (DCF)

0.0 0.2 0.4 0.6 0.8 1.0

Frequency

0

200400600800

FrequencyFrequency
Organ Dose Distribut

Organ Dose Distribu

 Normal Distribution Normal Distribution

• 7.49 ± 2.23 7.49 ± 2.23 mSv•

χ2 = 425, KS = 0.435 = 425, KS = 0.435 

 Lognormal Distribution Lognormal Distribution

• GM = 7.15 GM = 7.15 mSv• GSD = 1.36 GSD = 1.36•

χ2 = 283, KS = 0.349 = 283, KS = 0.349

Total Org

0.00 2.00 4.00 6.00 

Frequency

0

200400600800
Summary Summary

Organ Dose Uncerta

Organ Dose Uncerta

 Laboratory Uncertainty Laboratory Uncertainty

• Dosimeter Reading Dosimeter Reading• Missed Dose Uncertainty Missed Dose Uncertainty

 Field Uncertainty Field Uncertainty

• Photon Energy Photon Energy• Exposure Geometry Exposure Geometry