Bronchial Dose Research Articles

CELLULAR DOSE DISTRIBUTIONS OF INHALED RADON PROGENY AMONG DIFFERENT LOBES OF THE HUMAN LUNG.

Basal and secretory cell doses in the different lobes of the human lung following inhalation of short-lived radon progeny were calculated for a five-lobe asymmetric, stochastic lung model, considering the non-uniform ventilation of the lobes. Dose calculations for defined exposure conditions revealed that the upper lobes receive higher doses than the average bronchial dose for the whole lung, with the right upper lobe receiving the highest dose. The resulting inter-lobar distribution of cellular bronchial doses indicated that the non-uniform lung morphometry is the dominating factor, while non-uniform ventilation only slightly enhances the lobar differences. The comparison of average lobe-specific bronchial doses with the average bronchial dose for the whole lung allows the calculation of lobe-specific dose weighting factors, which can be used to convert average bronchial doses based on symmetric airway generation or bronchial compartment models to lobar bronchial doses.

A Review of Radon Equilibrium Factors in Underground Mines, Caves, and Thermal Spas.

Radon equilibrium factor Feq is an important factor in radon progeny dose assessment. A review of published measurements of Feq shows a range of values from 0.1 to 1.0 reported in studies from more than 26 countries measured in 173 underground mines, and 136 show caves, tourist mines, and thermal spas. The average values of Feq are 0.38 in underground mines and 0.39 for show caves, tourist mines, and thermal spas. The wide range of Feq in those special workplaces suggests that location-, environment-, and operation-specific values are more appropriate than a recommended average value in the calculation of lung bronchial dose. This is especially important in mines or other typically high radon exposure locations because Feq can be used for recording an individual's occupational radon exposure or dose.

Radon as a Tracer of Lung Changes Induced by Smoking

After smoking, exposure to radon and its progeny is the second leading cause of lung cancer. The probability of inducing lung carcinomas by inhaled radon progeny depends on the deposited radiation dose, and is significantly affected by physiological and morphometric changes induced by smoking. Due to irritation of the airways, the inhalation of cigarette smoke leads to the hyperproduction of mucus. Two concurrent processes occur: on one hand, increased production of mucus protects the target cells against radiation damage; on the other hand, in the case of long-term smokers, a chronic lung obstruction develops, causing an increase in the radiation dose to the lungs. Depending on the duration and intensity of smoking, these processes contribute to the final radiation dose with different weights. The primary objective of this study was to investigate to what extent these smoke-induced changes can modify the resulting absorbed dose of inhaled radon progeny relative to healthy nonsmokers. Since the bronchial dose depends on the degree of lung tissue damage, we have used this dose as a tool for detecting the effects of smoking on the lung epithelium. In other words, the biological effect of radon served as a tracer of changes induced by smoking.

Proposal and optimization of method for direct determination of the thoron progeny concentrations and thoron equilibrium

Most studies focused on thoron have shown that indoor thoron originates mainly from building materials and that thoron concentrations exponentially decrease with a distance from a wall surface. On the contrary, due to longer half-lives of thoron progenies, 212Pb and 212Bi, which are mainly responsible for the bronchial dose, it is expected that their spatial distribution is homogeneous. Therefore, direct measurements of thoron progeny concentrations or direct thoron measurement and determination of thoron equilibrium factor are necessary for accurate dose assessment. In this paper, we have optimized and validated a reliable and inexpensive method for direct measurement of thoron progenies concentrations based on an air filtration followed by gamma spectrometry measurements. With simultaneous measurements of indoor thoron by the RAD7 active device, the equilibrium factor for thoron in 15 different investigated dwellings was estimated. Obtained results for the equilibrium equivalent thoron concentrations in the range from 0.277 Bq/m3 to 11.34 Bq/m3 and thoron equilibrium factor in the range from 0.0047 to 0.098 with arithmetic mean value of 0.034 are in good agreement with already published results.

A Review of Indoor and Outdoor Radon Equilibrium Factors-part I: 222Rn.

Radon exposure limits are given in terms of radon gas concentration in the air. However, in the calculation of radon dose to the lung, the radon equilibrium equivalent concentration is used. The measured equilibrium factor times the measured radon gas concentration estimates the equilibrium equivalent concentration. Therefore, the equilibrium factor is an important factor in radon dose calculations. A review of published measurements of equilibrium factors shows a range of values reported in studies from more than 20 countries, measured in indoor residential, indoor public, and outdoor environments. Values for Rn are reported and discussed here, with special attention paid to results from India and China, where measured equilibrium factors are reported for hundreds and thousands of households, respectively. The wide range of equilibrium factors suggests that location-specific values are more appropriate than a worldwide average value in the calculation of lung bronchial dose.

A Review of Indoor and Outdoor Radon Equilibrium Factors-part II: 220Rn.

Radon exposure levels are given in terms of radon gas concentration in the air. However, in the calculation of radon dose to the lung, the radon equilibrium equivalent concentration is used. The measured equilibrium factor times the measured radon gas concentration estimates the equilibrium equivalent concentration. Therefore, equilibrium factor is an important factor in radon dose calculations. A review of published measurements of equilibrium factors shows a range of values reported in studies from more than 13 countries and regions measured in indoor residential, indoor public, and outdoor environments. Values for Rn are reported and discussed here as the second of a two-part series, with special attention paid to results from India and China, where measured equilibrium factors are reported for hundreds and thousands of households, respectively. The wide range of measured equilibrium factors suggests that location-specific values measured in the typical breathing zone are more appropriate than a worldwide average value in the calculation of lung bronchial dose.

Effect of Residential Radon Decay Product Dose Factor Variability on Reporting of Dose.

Guidelines for occupational exposure to radiation are based on annual absorbed or effective dose. Guidelines for Rn exposure are currently based on air concentrations of Rn or decay products. Models of bronchial dose from decay product exposure are based on calculations that have five major parameters with parameter variabilities ranging from 20 to 50%. Many countries currently use the ICRP dose conversion convention, which is a ratio of lifetime Rn lung cancer risk to lifetime atomic bomb dose risk. The results of ongoing epidemiology changed both lifetime risk values, and the dose conversion convention has increased by a factor of 2. Therefore, the current dose conversion convention risk ratio is to be replaced by biokinetic dosimetric models. The main effect of variability in the value of Rn dose factors on industry is that the workplace atmosphere must be characterized accurately, and at present, this is not possible. A history of the dose factor models is central to factor development. The values of the dose model parameters are described illustrating the difficulty in calculation of a dose factor with universal applicability. The objective is to show the range of each parameter and the effect of the dose factor used when reporting occupational or residential bronchial dose.

Stochastic rat lung dosimetry for inhaled radon progeny: a surrogate for the human lung for lung cancer risk assessment.

Laboratory rats are frequently used in inhalation studies as a surrogate for human exposures. The objective of the present study was therefore to develop a stochastic dosimetry model for inhaled radon progeny in the rat lung, to predict bronchial dose distributions and to compare them with corresponding dose distributions in the human lung. The most significant difference between human and rat lungs is the branching structure of the bronchial tree, which is relatively symmetric in the human lung, but monopodial in the rat lung. Radon progeny aerosol characteristics used in the present study encompass conditions typical for PNNL and COGEMA rat inhalation studies, as well as uranium miners and human indoor exposure conditions. It is shown here that depending on exposure conditions and modeling assumptions, average bronchial doses in the rat lung ranged from 5.4 to 7.3 mGy WLM(-1). If plotted as a function of airway generation, bronchial dose distributions exhibit a significant maximum in large bronchial airways. If, however, plotted as a function of airway diameter, then bronchial doses are much more uniformly distributed throughout the bronchial tree. Comparisons between human and rat exposures indicate that rat bronchial doses are slightly higher than human bronchial doses by about a factor of 1.3, while lung doses, averaged over the bronchial (BB), bronchiolar (bb) and alveolar-interstitial (AI) regions, are higher by about a factor of about 1.6. This supports the current view that the rat lung is indeed an appropriate surrogate for the human lung in case of radon-induced lung cancers. Furthermore, airway diameter seems to be a more appropriate morphometric parameter than airway generations to relate bronchial doses to bronchial carcinomas.

Application of a Monte Carlo lung dosimetry code to the inhalation of thoron progeny.

To determine radiation doses incurred by inhaled thoron progeny, the Monte Carlo radon progeny lung dosimetry code IDEAL-DOSE was adapted to the inhalation of thoron progenies, comprising the alpha-emitting nuclides 216Po, 212Bi and 212Po. Dose calculations for defined exposure conditions yielded a dose conversion coefficient (DCC) of 4.6 mSv WLM(-1) or 94.2 nSv (Bq h m(-3))(-1) when compared with a DCC of 3.8 mSv WLM(-1) if based on the International Commission on Radiological Protection Human Respiratory Tract Model. Bronchial doses were computed for different thoron progenies exposure conditions measured in a Bavarian half-timbered house and in a thoron experimental house at the Helmholtz Zentrum München. DCCs ranged from 4.9 to 12.9 mSv WLM(-1), depending on particle size, unattached fraction and fractional activity concentrations. For exposure-specific indoor aerosol parameters, the thoron progeny DCC is smaller than the radon progeny DCC by about a factor of 2.

Stochastic dosimetry model for radon progeny in the rat lung.

The stochastic dosimetry model presented here considers the distinctly asymmetric, stochastic branching pattern reported in morphometric measurements. This monopodial structure suggests that an airway diameter is a more appropriate morphometric parameter to classify bronchial dose distributions for inhaled radon progeny than the commonly assigned airway generation numbers. Bronchial doses were calculated for the typical exposure conditions reported for the Pacific Northwest National Laboratory rat inhalation studies, yielding an average bronchial dose of 7.75 mGy WLM(-1). If plotted as functions of airway generations, the resulting dose distributions are highest in the central bronchial airways, while significantly decreasing towards peripheral generations. However, if plotted as functions of airway diameters, doses are much more uniformly distributed among bronchial airways. The comparison between rat and human lungs indicates that dose conversion coefficients for the rat lung are higher than the corresponding values for the human lung by a factor of 1.34 for the experimental PNNL exposure conditions, and of 1.25 for typical human indoor conditions.

Retrospective Cohort Study of Bronchial Doses and Radiation-Induced Atelectasis After Stereotactic Body Radiation Therapy of Lung Tumors Located Close to the Bronchial Tree

To evaluate the dose-response relationship between radiation-induced atelectasis after stereotactic body radiation therapy (SBRT) and bronchial dose. Seventy-four patients treated with SBRT for tumors close to main, lobar, or segmental bronchi were selected. The association between incidence of atelectasis and bronchial dose parameters (maximum point-dose and minimum dose to the high-dose bronchial volume [ranging from 0.1 cm(3) up to 2.0 cm(3)]) was statistically evaluated with survival analysis models. Prescribed doses varied between 4 and 20 Gy per fraction in 2-5 fractions. Eighteen patients (24.3%) developed atelectasis considered to be radiation-induced. Statistical analysis showed a significant correlation between the incidence of radiation-induced atelectasis and minimum dose to the high-dose bronchial volumes, of which 0.1 cm(3) (D(0.1cm3)) was used for further analysis. The median value of D(0.1cm3) (α/β = 3 Gy) was EQD(2,LQ) = 147 Gy3 (range, 20-293 Gy3). For patients who developed atelectasis the median value was EQD(2,LQ) = 210 Gy3, and for patients who did not develop atelectasis, EQD(2,LQ) = 105 Gy3. Median time from treatment to development of atelectasis was 8.0 months (range, 1.1-30.1 months). In this retrospective study a significant dose-response relationship between the incidence of atelectasis and the dose to the high-dose volume of the bronchi is shown.

A Retrospective Study of Bronchial Doses and Radiation-induced Atelectasis After SBRT of Lung Tumors Located Close to the Bronchial Tree

A Retrospective Study of Bronchial Doses and Radiation-induced Atelectasis After SBRT of Lung Tumors Located Close to the Bronchial Tree

LONG TERM MEASUREMENTS OF INDOOR RADON EQUILIBRIUM FACTOR

To provide detailed information for bronchial dose estimates, aerosol particle size distributions, and radon gas concentration, measurements were made in six residential homes and three laboratory rooms in different office buildings in the city of Ottawa. In the literature, most particle size distribution measurements are taken with samplers operating for a few days at most. In this study, the particle size samplers collected the samples from 77 to 162 d. The equilibrium factor determined from the long-term measurements ranged from 0.6 to almost 1 with an average of 0.75. Even though radon concentrations were quite different between residential setting and office buildings, the average equilibrium factor was similar in the two different indoor environments. The results suggest that at least in some basements, if they were occupied, the radon dose would be about twice as high as normally estimated from the conventional F(eq) value of 0.4.

Radon lung dosimetry models

Two different modelling approaches are currently used to calculate short-lived radon progeny doses to the lungs: the semi-empirical compartment model proposed by the International Commission on Radiological Protection and deterministic and stochastic airway generation models. The stochastic generation model IDEAL-DOSE simulates lung morphometry, transport, deposition and clearance of inhaled radionuclides, and cellular dosimetry by Monte Carlo methods. Specific dosimetric issues addressed in this paper are: (1) distributions of bronchial doses among and within bronchial airway generations; (2) relative contributions of radon progeny directly deposited in a given airway generation and those passing through from downstream generations to the bronchial dose in that generation; (3) distribution of bronchial doses among the five lobes of the human lung; (4) inhomogeneity of surface activities and resulting doses within bronchial airway bifurcations; (5) comparison of bronchial doses between non-smokers and smokers; (6) relative contributions of sensitive target cells in bronchial epithelium to lung cancer induction and (7) intra- and intersubject variations of bronchial doses.

MODELING INTERSUBJECT VARIABILITY OF BRONCHIAL DOSES FOR INHALED RADON PROGENY

The main sources of intersubject variations considered in the present study were: (1) size and structure of nasal and oral passages, affecting extrathoracic deposition and, in further consequence, the fraction of the inhaled activity reaching the bronchial region; (2) size and asymmetric branching of the human bronchial airway system, leading to variations of diameters, lengths, branching angles, etc.; (3) respiratory parameters, such as tidal volume, and breathing frequency; (4) mucociliary clearance rates; and (5) thickness of the bronchial epithelium and depth of target cells, related to airway diameters. For the calculation of deposition fractions, retained surface activities, and bronchial doses, parameter values were randomly selected from their corresponding probability density functions, derived from experimental data, by applying Monte Carlo methods. Bronchial doses, expressed in mGy WLM-1, were computed for specific mining conditions, i.e., for defined size distributions, unattached fractions, and physical activities. Resulting bronchial dose distributions could be approximated by lognormal distributions. Geometric standard deviations illustrating intersubject variations ranged from about 2 in the trachea to about 7 in peripheral bronchiolar airways. The major sources of the intersubject variability of bronchial doses for inhaled radon progeny are the asymmetry and variability of the linear airway dimensions, the filtering efficiency of the nasal passages, and the thickness of the bronchial epithelium, while fluctuations of the respiratory parameters and mucociliary clearance rates seem to compensate each other.

Thoron versus radon: measurement and dosimetry

Two new instruments were developed for the U.S. Department of Energy Environmental Science Management Program (EMSP) to perform more detailed exposure assessment measurements at Fernald, OH. Fernald is a former uranium processing facility undergoing remediation. The instruments are a miniature radon and thoron detector, and a miniature particle size spectrum analyzer. Ongoing measurements of both thoron ( 220Rn) and radon ( 222Rn) gas are now being made at four locations: (1) at Fernald; (2) at the New York City National Weather Service site, used as a quality control (QC) site; (3) at a private home in Bangkok used as a QC site; and (4) at a research center and rare earth development facility processing monazite ore near Bangkok. Particle size distribution measurements are presented for two locations: at Fernald and at the Rare Earth Facility near Bangkok. Continuous radon and thoron measurements were made at all sites for at least 1 year and the bronchial dose is reported.

Bronchial dosimeters for radon progeny for Chinese males and females

Bronchial dosimeters have been designed for adult Chinese males and females for home and mine exposures, which can give the bronchial doses from radon progeny by direct measurements. The bronchial dosimeter for home exposures consists of five 400-mesh wire screens. With a sampling face velocity of 3.3 cm s –1 for Chinese males and 2.7 cm s –1 for Chinese females, the deposition pattern on the wire screens were found to satisfactorily match the variation of the dose conversion coefficients (in units of mSv WLM –1) with the size of radon progeny from 1 to 1000 nm. The bronchial dosimeter for mine exposures consists of four 250-mesh wire screens. With a sampling face velocity of 3.3 cm s –1, the deposition pattern on the wire screens were found to satisfactorily match the variation of the dose conversion coefficients for both Chinese males and females. In this way, the bronchial dosimeters directly give the bronchial doses from the alpha counts recorded on the wire-screens.

Bronchial dosimeter for radon progeny

A true bronchial dosimeter has been designed, consisting of four 400-mesh wire screens and a filter paper. With a face velocity of 3.3cms–1 for home exposure and 4.6cms–1 for mine exposure, the deposition pattern on the wire screens were found to satisfactorily match the variation of the dose conversion factor (in units of mSvWLM–1) with the size of radon progeny from 1 to 1000nm. In this way, the bronchial dosimeter directly gives bronchial dose from the alpha counts recorded on the wire-screens and the filter paper. Calculations of the dose conversion coefficient (DCC) using the proposed bronchial dosimeter and the lung dosimetric model were performed for typical aerosol characteristics. Values obtained from the bronchial dosimeter yielded overestimates of the DCC by 11.1% and 2.4% for typical home and mine conditions, respectively.

Bronchial Rn dose survey for residences

The bronchial dosimeter for Rn progeny proposed by Yu and Guan in 1998 was employed to survey the bronchial dose from Rn progeny in 30 residences in Hong Kong. An average bronchial deposition fraction of Rn progeny was obtained as 0.0334, which gave an average dose conversion factor (DCF) of 8.5 mSv WLM −1. The mean values of potential α energy concentration (PAEC) deposited in the tracheobronchial region (PAEC T−B), total PAEC in air (PAEC T), annual effective dose ( E), concentration of Rn gas (RC) and annual dose conversion factor (ADCF) for all the residential sites combined were 0.11±0.05, 3.1±1.4 mWL, 1.2±0.5 mSv yr −1, 23±10 Bqm −3 and 0.055±0.020 (mSv yr −1 per Bqm −3), respectively, with air-conditioned sites (AC sites) and non-AC sites having significantly different mean ADCF values. The indoor relative humidity affected PAEC T and RC PAEC T−B and E with high confidence levels (>95%).

Lung Dosimetry for Thorotrast Patients: Implications for Inhalation of Radon Progeny

A peculiar feature of radiation-induced carcinogenesis in German Thorotrast patients is that no excess lung cancers have been observed so far in the epidemiological follow-up study. Two possibilities have been explored here to explain the apparent discrepancy between predicted and observed bronchial tumors: (1) Bronchial doses are smaller than presently predicted; and/or (2) lung cancer risk per unit exposure in Thorotrast patients is smaller than that derived from inhalation of (222)Rn progeny. First, the mean bronchial doses computed with an updated dosimetric model for the different radiation sources are indeed substantially smaller than previous dose estimates; however, the epidemiological findings still cannot be explained in terms of bronchial doses. Second, lung cancer risk estimates based on the revised dose estimates and relative risk coefficients specifically derived from chronic indoor exposures still yield a relative risk of 1.66 for the German Thorotrast patients. This suggests that either the lung cancer risk coefficient for inhalation of radon progeny cannot be applied to Thorotrast patients because of differences in dose distributions or exposure conditions, or the current tissue weighting factor should be applied primarily to the bronchial region of the lung in the case of exposure to radon progeny.