Quantifying uncertainties in lung dosimetry with application to plutonium oxide aerosols

452 Pages·1995·11.4 MB·English

by  Huston, Thomas Edward

QUANTIFYINGUNCERTAINTIES IN LUNGDOSIMETRY WITH APPLICATION
TO PLUTONIUM OXIDE AEROSOLS
By
THOMAS EDWARD HUSTON
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1995
Dedicated to Rhonda, my wife and friend-
without her encouragement this work would have been impossible.
ACKNOWLEDGMENTS
This work has been supported in part by Grant Number R23/CCR409769-01 from
the Centers for Disease Control and Prevention (CDC); however, its contents are solely
the responsibility ofthe author and do not necessarily represent the official view ofCDC.
Preliminary portions ofthe research were performed under appointment to the
Environmental Restoration and Waste Management Fellowship Program administered by
Oak Ridge Institute for Science and Engineering for the United States Department of
Energy. I am especially grateful to these agencies for providing the financial assistance
necessary to complete this work.
I wish to thank my supervisory committee members-Drs. William G Vernetson
(chair), W. Emmett Bolch (cochair), Marc Jaeger, David E. Hintenlang, William S.
Properzio, and Wesley E. Bolch~for serving on the committee and for their guidance
during the course ofthis study. I am especially thankful to Drs. William Vernetson,
Emmett Bolch, and Marc Jaeger fortheir useful suggestions to improve content in early
draft versions ofthe manuscript. I offer a special note ofthanks to Dr. Emmett Bolch,
who during the past two years provided me (through the resources ofthe CDC grant) with
the financial backing to complete this research; his care for students is indeed a credit to
his profession.
in
I am thankful to several others with whom I have had the privilege ofassociating
throughout various stages ofthis work. These persons include, among many others, Drs.
Gen Roessler, John Till, Helen Grogan, Tony James, and Alan Birchall. Dr. Gen Roessler
served as a point ofcontact for me during the early stages ofthis work. She introduced
me to Dr. Till, who (along with colleagues from Radiological Assessments Corporation)
expressed a need for quantitative information regarding uncertainties in lung dose
predictions for plutonium. Dr. Till assisted during the early stages ofthis work by helping
me obtain draft reports from the National Council on Radiation Protection and
Measurements (NCRP) and the International Commission on Radiological Protection
(ICRP). At that time, both agencies were in the process ofreleasing independent models
for respiratory tract dosimetry. I appreciate the willingness ofthe ICRP and NCRP to
release these draft reports to me before publication. Drs. Tony James and Alan Birchall
provided me with many useful materials and encouragement. Dr. Helen Grogan provided
several helpful comments throughout the work.
I would like to thank my wife, Rhonda, for her constant encouragement
throughout my "tenure" at the university. She kept me focused on my work, never
complaining about the long hours I kept. She also helped organize the reference section
ofthe manuscript. I have been truly blessed with a wonderful, caring wife and a best
friend. I certainly look forward to spending the rest ofmy life (yes, I do plan to get one
aftergraduation) with her. I want to thank our new son, Hayden Edward Huston (born
IV
only days ago on July 24, 1995), for bringing me happiness and wonder while I have
prepared this manuscript.
I would like to thank some (past and present) fellow students, Kaiss Al-Ahmady,
Brian Birky, Thabet Tolaymat, George Harder, Louis Iselin, Susan Stanford, and Missy
Jones, among others, for their friendship and stimulating discussions regarding the
radiation sciences. I also appreciate the departmental staffin the Nuclear Engineering
Sciences office (Barbara, Joan, Beth, Cess, and Donna) and the Environmental
Engineering Sciences office (Sandy, Berdenia, and Shirley). Thanks also to Chuck, Al,
Gene, and Gary forproviding me with an outlet to this insanity by way ofthe Tuesday
night trombonejazz sessions.
Finally, but certainly not least, I am very thankful to all ofmy family and friends
back home in Arkansas for giving me hope and encouragement throughout the many,
many years ofmy education. I miss them all greatly.
.
TABLE OF CONTENTS
page
ACKNOWLEDGMENTS
iii
LIST OF TABLES
x
LIST OF FIGURES
xjv
ABSTRACT
xvlii
CHAPTERS
INTRODUCTION
1
1
1.1 Purpose ofStudy 3
1.2. Background Information 4
1.2.1. Radiation Exposure Pathways 4
1.2.2. Internal Radiation Dosimetry, Reference Man, and Risk 9
1.2.3 Advantages and Disadvantages ofthe Reference Man Approach 14
1.3. Previous Work 16
1.4. Description ofPresent Study 20
1.4.1. Assessment Problem Addressed 20
1.4.2. Units ofExposure 22
1.4.3. Summary ofthe Research Approach 24
2 METHODS FOR RESPIRATORY TRACT MODELING 27
2.1. Introduction 27
2.2. Development ofRespiratory Tract Dose Models 31
2.3. Respiratory Tract Morphological Model 33
2.4. Respiratory Tract Deposition Model 35
2.5. Particle Size and Diffusion Characteristics 48
2.6. Respiratory Tract Clearance Model
51
2.7. Respiratory Tract Dose Model 63
2.8. Summary 70
vi
page
METHODS FOR CONDUCTINGPARAMETER UNCERTAINTY
3
ANALYSES
72
3.1. Introduction 72
3.2. Quantifying Parameter Correlations and Uncertainties 75
3.2.1. Parameter Correlations 75
3.2.2. ParameterUncertainties 78
3.2.3. Testing the Fit ofan Assigned Distribution 84
3.2.4. Subjective Probability Judgements and Expert Opinion 86
3.3. Propagation ofParameter Uncertainty 88
3.3.1. Simple Random Sampling 89
3.3.2. Latin Hypercube Sampling 91
3.4. Presentation ofUncertainties in Model Predictions 96
3.5. Parameter Sensitivity Techniques 97
3.6. Description ofthe Lung Dose Uncertainty Code (LUDUC) 102
3.7. Summary 109
4 UNCERTAINTIES IN RESPIRATORY TRACT MODEL PARAMETERS 110
4.1 Deposition Model Parameters 112
4.1.1. BodyHeight 112
4.1.2. Body Mass Index 116
4.1.3. Airway Diameters and Lengths 123
4.1.4. Anatomical Dead Space
131
4.1.5. Regional Volumes ofthe Respiratory Tract 135
4.1.6. Functional Residual Capacity 137
4.1.7. Vital Capacity 139
4.1.8. Ventilation Rate and Volumetric Flow Rate 141
4.1.9. Tidal Volume 160
4.1.10. Fraction ofAir Breathed Through the Nose 169
4.1.1 1. Uncertainty in Particle Inhalability 174
4.1.12. Regional Deposition Efficiency Uncertainty 176
4.2. Clearance Model Parameters 179
4.2.1. Introduction 179
4.2.2. Partition ofDeposition in Clearance Model Compartments ... 180
4.2.3. Fractional Clearance Rate Constants 188
4.2.4. Absorption Rate Constants 190
4.3. Dose Model Parameters 200
4.3.1. Introduction 200
4.3.2. Measurements ofthe Bronchial Epithelium and Critical
Cell Layers 201
Vll
page
4.3.3. Extrathoracic Regions 207
4.3.4. Bronchial Region 207
4.3.5. Bronchiolar Region 214
4.3.6. Surface Area ofBronchial and Bronchiolar Regions 219
4.3.7. Alveolar-Interstitial Region 222
4.3.8. Total Lung Mass 223
4.3.9. Mass ofLymph Nodes 225
4.3.10. Regional Risk-Apportionment Factors 226
4.3.11. Summary ofMethods forDose Model Parameters 228
5 APPLICATION OF LUDUC TO INHALED PLUTONIUM OXIDE
AEROSOLS: RESULTS AND DISCUSSION
231
5.1. Introduction 231
5.2. Characteristics of239Pu0 Aerosols 233
2
5.3. Dose Uncertainty Results for Inhaled ^uO;, Aerosols 237
5.3.1. Exposure Scenario and Notational Conventions 237
5.3.2. Adult Males Exposed to "'PuOj Aerosols 239
5.3.3. Influence ofDose Integration Time 249
5.3.4. Influences ofAge and Gender 252
5.3.5. Influences ofParticle Size Dispersion 256
5.4. Dose Sensitivity Results for Inhaled ^uOz 264
5.4.1. Combined Lung Dose 266
5.4.2. Regional Tissue Doses 270
5.5. Deposition Sensitivity Results 279
5.5.1. Bronchial Region 283
5.5.2. Bronchiolar Region 283
5.5.3. Alveolar-Interstital Region 284
5.6. Implications ofDose Results and Comparison to Reference Man Dose 285
.
5.7. Summary ofResults 292
6 CONCLUSIONS AND RECOMMENDATIONS
296
6.1. Summary ofResearch 296
6.2. Conclusions Based on Results forPlutonium Oxides 300
6.3. Recommendations for Future Research 305
vin
page
APPENDICES
A COMPARISON OF ICRP AND NCRP MODELS
311
B THE CLEARANCE MODEL: SYSTEM OF DIFFERENTIAL
EQUATIONS
323
C DOSE CALCULATIONS IN TRACHEOBRONCHIAL AIRWAYS
330
D TIDAL VOLUMES FOR CHILDREN
355
E DOSE DATA FOR INHALATION OF PLUTONIUM OXIDE
364
REFERENCES
410
BIOGRAPHICAL SKETCH
429
IX
LIST OF TABLES
Table ^age
1-1 Selected intake-to-dose conversion factors for inhalation ofsome plutonium
.
isotopes and other transuranics 11
1-2. Organ and total risk per inhalation intake ofplutonium compounds 12
1-3. Specific information related to the assessment question and scenarios
considered in this study 21
2-1 Recommended parameters for use in model ofregional deposition forthe
fraction ofintake inhaled and exhaled through the nose for any subject as
functions ofrespiratory variables and anatomical size 42
2-2. Recommended parameters foruse in model ofregional deposition forthe
fraction ofintake inhaled and exhaled through the mouth for any subject, as
functions ofrespiratory variables and anatomical size 43
2-3 Description ofinput parameters required by the revised ICRP deposition
.
model
44
2-4. Other parameters ofuse in modeling particle deposition in the respiratory
tract 45
2-5. Reference values for mechanical clearance rates in the particle transport
aspect ofthe ICRP human respiratory tract model 56
2-6. Reference values for partition ofdeposit among compartments in region. ... 56
2-7. Assignment ofcompartments to source regions for short-range radiations in
the revised ICRP respiratory tract model 66
2-8. Risk-apportionment factors recommended by the ICRP for weighting the
dose to various respiratory tract target tissues 69
3-1. Main steps involved in conducting a parameter uncertainty analysis 74
x