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Lung dosimetry for Lung dosimetry for inhaled long-lived inhaled long-lived

radionuclides and radon radionuclides and radon progenyprogeny

M.Hussain, R. Winker-Heil and W. Hofmann

Division of Physics and Biophysics,Department of Materials Engineering and

Physics University of Salzburg

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IntroductionIntroduction• Stochastic lung dosimetry model IDEAL-DOSE considers deposition

in the whole bronchial and alveolar airway system, while clearance was restricted to bronchial airways.

• For inhaled long-lived radionuclides, alveolar clearance has also to be considered for the calculations of alveolar as well as the bronchial doses from subsequently cleared particles to the bronchial region.

• The ICRP task group on internal dosimetry is developing new Occupational Intake of Radionuclide (OIR) and in connection to OIR Human Respiratory Tract Model (HRTM) will be updated on the basis of new information and experience.

• The main consideration for updating the HRTM are two clearance mechanisms including:i. particle transportii. blood absorption from different regions of the lung

• Proposed particle transport rates for updating clearance model is incoporated in IDAEL-DOSE for estimating lung doses from LLR.

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ObjectivesObjectives

• Following are the primary objectives of this study i. the development of a stochastic

clearance model in the alveolar region. ii. the calculation of doses produced by

long-lived radionuclides in alveolar and bronchial regions on the basis of the revised HRTM clearance model.

Lung depositionLung deposition

• The lung is made up of group of airways called generations.

– Extrathoracis region– Tracheobronchial region– Alveolar region

• Deposition Mechanisms– Diffusion– Sedimentation– Impaction

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Extrathoracic region: impaction, sedimentation, electrostatic (particles > 1 μm)Tracheobronchial region:impaction, sedimentation, diffusion (particles < 1 μm)Alveolar region :sedimentation, diffusion (particles < 0.1 μm)

Particle ClearanceParticle Clearance

• Getting rid of deposited particles from the lung is called clearance

• The muco-ciliary escalator operates in the tracheobronchial region for clearance predominantly up to generation 12 and fading out at generation 16.

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Revision of HRTM clearance modelRevision of HRTM clearance model

• In the previous human respiratory tract model (HRTM) clearance model, clearance mechanisms are based on comparative transport rates of particles.

• The HRTM for the alveolar model has large uncertainties for particle clearance and hence doses delivered to the lung.

• The revised HRTM is based on new information and experimental data on insoluble particles being transported from different regions of the lung and on soluble particles with materials specific absorption rates.

• The revised HRTM predicts much slower alveolar clearance than the previous one and hence predicts higher doses in the lung.

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Calculation methodsCalculation methods

Alveolar clearanceAlveolar clearance•Following mechanism for alveolar clearance are considered

i. Macrophage mediated clearance from alveolar region to bronchiolar airways

ii. Particles escaped from the mechanism penetrate into interstitium and from there to hilar nymph nodes by slow clearance according to the rates shown in the figure below:

Particle residence times according to the updated model are calculated stochastically in the acinar region to find total disintegrations in alveolar compartments.

Alveolar clearanceAlveolar clearanceModelModel

Assumptions for dose calculationsAssumptions for dose calculations

• Alveolar clearance reached steady state conditions (rate of deposition equals rate of clearance)

• Breathing rate = 1.2 m3 h-1

• Exposure to LLR is considered as constant chronic intake over 365 days (with a mean of 0.8 h kBq m-

3)• Particle density = 3 g cm-3; shape factor = 1.5

(ICRP) AMAD = 1 and 5 µm• For Rn progeny, doses for 1 WLM of exposure is

calculated (i.e. 3.5x 10-3 Jh/m3) which is then converted to a real ore exposure conditions.

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ResultsResults

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Results (contd..)Results (contd..)

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Results (contd..)Results (contd..)

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Results (contd..)Results (contd..)

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Summary of resultsSummary of results

• Due to the long retention time in the lung and the long half life of LLRs, ore dust produces doses following exposure.

• Up to 70% of 50 years committed absorbed dose to BBbas and up to 20% to Al regions are delivered from LLRs.

• For 5 µm particles upto 2 times higher doses are delivered in the bb region from the particles cleared from the acinar region as compared to the directly deposited there.

• For 1 µm size particle up to 6 times higher doses in the bb region and about an equal amount of doses in BB region are delivered from the particles cleared from acinar region as compared to the particles directly deposited in these regions.

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ConclusionsConclusions

• New information available for particle transport and material specific absorption in different regions of the lung allows more realistic modeling for dose calculations in the lung.

• Implementation of updated alveolar clearance model in stochaustic lung model (IDAEL) predicts 2-6 times higher doses delivered in TB reion from the particles cleared from the acinar region as compared to the particles directly deposited in the TB region.

• Long lived alpha emitters in uranimum mines can deliver upto 5 percent of the doses allowed from the short lived radon daughters.

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Dankeschön