Multiple Path Particle Dosimetry Modeling (MPPD) · A four-component, multiple path, particle dosimetry model was developed to predict regional and local deposition of particles.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Multiple Path Particle Dosimetry Modeling (MPPD)
Bahman Asgharian Applied Research Associates, Inc., Raleigh, NC
Application, challenges and assumptions Dosimetry modeling of environmental aerosols Example #1 – Internal dose as a function of age Example #2 – Interspecies extrapolation Summary and Conclusions
Outline
3
Internal Dose in Risk Assessment Context
Exposure characteristics
Internal dose estimation
Dose distribution and fate in lung
Risk evaluation
4
Dosimetry Modeling Applications in risk Assessment
Particle transport Average properties across airway cross sections (1D modeling) Simplified BCs: Losses are included as a sink term
7
Calculate: Deposition fraction in the lung (per breath)- Regional (URT, TB, PUL, LRT, total)- Lobar- Site-specific
Given: Exposure environment - Aerosol concentration- Aerosol size distribution
Airway parametersLung and breathing parametersBreathing route & pattern
Reparatory Tract Deposition Modeling
Objective: Calculate internal dose in the respiratory tract.
8
Building a Computational Dosimetry Model
Exposure ‐> Inhalation ‐> Transport ‐> ‐> Clearance
Aerosol size distribution
ImpactionDiffusion
9
Four Components of Particle Respiratory Deposition Model
10
1. URT deposition modeling- Deposition fractions are from measurements or numerical computations- Develop semi-empirical equations as a function non-dimensional
parameters
2. Respiratory tract geometry- Scanned imagery for large airways and morphometry for small airways- TB: symmetric or asymmetric- PUL (A): symmetric due to the large number and random orientations
made up of tracheobronchial tree and alveolar sub-tree.
Tree geometry: symmetric, asymmetric, and monopodialSymmetric: both daughters identical - typical pathAsymmetric/monopodial : daughters have different dimensions and orientations
Symmetric structure: Average deposition lung per depth
Asymmetric geometries:- Are more accurate representations that allow for site-specific dose prediction.
- Require better data sources (have for the rat) and are more involved mathematically
15
LRT GeometriesRats (Monopodial)
Asymmetric
Humans
Reconstructed
SymmetricTypical-path
Asymmetric lung
5 symmetric lobes
16
Third Component: Lung Ventilation
PInspiration Expiration
IntrapleuralPressure
AlveolarPressure
Inspiration
Expiration
17
Two Ventilation Models Were Developed
Steady breathing (uniform lobe expansion):˗ Normal breathing – HEC calculations, risk assessment˗ Airflow rate is proportional to distal volume.
Unsteady breathing (RLC network analysis):˗ Diseased lung, HFV, more detailed calculations.˗ Flow rate is proportional to R, C, and L.˗ Flow splitting is proportional C of branches.
P
d1
d2
p
18
Fourth Component: Particle Transport Modeling
19
Depositiontransport
massNettransport
massNetchange
number/Mass
ConvectionDiffusion
Particle Transport Equations
Calculate particle concentration from a mass balance in an airway:
Particle concentration and deposition are calculated for all airways of the lung from the above models