Biomedical subjects

D Nikezic

Publications and source records attributed to D Nikezic.

27 records · Page 2Linked to original sources

PubMed2002

Sensitivity of LR115 detector in diffusion chamber to 222Rn in the presence of 220Rn.

Determination has been made of the sensitivity of LR115 type 2-track detectors (in units of m) to 222Rn, measured in the presence of 220Rn. Measurements have been made by means of a widely used diffusion chamber while Monte Carlo simulations have also been conducted. The experimentally derived sensitivities for 222Rn and 220Rn were found to be 0.470+/-0.022 and 0.486+/-0.042 m, respectively. For Monte Carlo simulations, the sensitivities to 222Rn gas were found to range from 0.618 x 10(-2) m (assuming that all 218Po progeny decay before deposition onto the internal walls of the diffusion chamber) to 0.405 x 10(-2) m (assuming that all 215Po progeny are deposited on the internal walls of the same containment vessel before decaying). The sensitivity to 220Rn gas of 0.465 x 10(-2) m found from Monte Carlo simulations agrees to within uncertainty with experimental findings. The experimentally derived sensitivity value for 222Rn indicates that 30% of the 218Po progeny decay before deposition onto the internal walls of the diffusion chamber.

Computer Simulation↗

PubMed2002

Alpha-particle lineal energy spectra for the human lung.

PURPOSE: To determine the distribution of lineal energy in the target cells and the parameters of distribution for various combinations of sources, targets and energies in the human tracheobronchial tree. Frequency average and average of the square of the lineal energy were also calculated from the lineal energy distribution. METHOD: A model was created to simulate the geometric distribution of cell nuclei in the airway of the tracheobronchial tree. Propagation of alpha particles in such a model was simulated by the Monte Carlo method. Microdosimetric distributions of lineal energy were calculated. RESULTS: Distributions of lineal energy were substantially different for basal and secretory cells. The frequency average of specific energy was found to be between 0.3 Gy and 0.4 Gy. CONCLUSIONS: Interactions of alpha particles with basal and secretory cells show significant differences: events with small energy transfer are dominant for basal cells, while those with large transfer are dominant for secretory cells. This finding can influence dose weightings and yield lower values of the dose-to-exposure coefficient.

Alpha Particles↗

PubMed2002

Distributions of specific energy in sensitive layers of the human respiratory tract.

The purpose of the present work was to calculate the specific energy distribution in sensitive cells of the human lung. Specific energy distributions were calculated by applying Monte Carlo methods and the ICRP 66 model of the human respiratory tract. Specific energies were calculated at various depths in the epithelium and combined according to the relative cell abundance. Distributions are given for various combinations of sources, alpha-particle energies, targets and regions of the lung. The chord length does not follow the triangular distribution when the particle range is comparable to the diameter of the target. The notion of "effective volume" is introduced and defined, which is needed for estimation of hit frequency in some particular targets. It has been shown that basal cells are subjected to a larger proportion of alpha-particle hits with small energy transfer than secretory cells. Small energy transfer events that lead to minor damage of the DNA are more efficient in cancer induction than are hits with large energy deposition that lead to cell killing.

Alpha Particles↗

PubMed2001

Indoor dose conversion coefficients for radon progeny for different ambient environments.

Inhaled progeny of 222Rn (radon progeny) are the most important source of irradiation of the human respiratory tract. Their attachment to atmospheric aerosols follows a well-established relationship between the activity size distribution (ASD) and the number size distribution. Recent studies have shown that indoor aerosols are derived primarily from outdoor sources, so it is pertinent to study the effects of different ambient environments on the indoor radon dose (in terms of the dose conversion coefficient or DCC, in units of mSv WLM-1). Commonly encountered ambient aerosols were studied here, which included the traffic-, urban-, and marine-influenced aerosols. The ASDs of attached radon progeny for all three studied ambient environments were well-represented by normal distributions. From these ASDs, the DCCs were calculated using the ICRP66 model and the scaled Yeh-Schum model. All other employed parameters were adopted from original references or authoritative reports. The DCCs for a nominal home calculated using the James model and the Yeh-Schum model were 12 and 8 mSv WLM-1, respectively. The DCCs were largest for urban-influenced ambient environments and smallest for marine-influenced ambient environments, and those for traffic-influenced ambient environments were close to that for a nominal home. If we adopt the stochastic model, the probability of contracting radon-induced lung cancer by a person living with a marine-influenced ambient environment will be half that of a person living with an urban-influenced ambient environment.

Aerosols↗

PubMed2001

Microdosimetric calculation of absorption fraction and the resulting dose conversion factor for radon progeny.

It is an established fact that radon progeny can induce lung cancers. However, there is a well-known discrepancy between the epidemiologically derived dose conversion factor for radon progeny (4 mSv/WLM) and the dosimetrically derived value (15 mSv/WLM) (mSv is a unit of the dose while WLM is a unit of exposure to radon progeny). Up to now there is no satisfactory explanation to this. In the present study we propose that microdosimetry will help reduce the discrepancy significantly. The ICRP Human Respiratory Tract Model (HRTM) has been applied to calculate the effective dose conversion factor. All parameters have been kept at their best estimates. Modifications were made in the calculation of the absorbed fractions of alpha particles. In contrast to the ICRP approach where the energy has been considered to be deposited in the layer containing the sensitive cells, we used a microdosimetric approach in which the alpha particles deposit their energy only in the nuclei of sensitive cells. This modification alone has lowered the dose conversion factor by about one-third (from 15 mSv/WLM down to approximately 10 mSv/WLM).

Cell Nucleus↗

PubMed2001

Radon progeny dose conversion coefficients for Chinese males and females.

The airway dimensions for Caucasian males have been scaled by multiplying by factors 0.95 and 0.88 to give those for Chinese males and females, respectively. Employing the most recent data on physical and biological parameters, the radiation doses to the basal and secretory cells due to alpha particles from 218Po and 214Po, homogeneously distributed in the mucous layer, have been calculated. The emission of alpha particles has been simulated by a Monte Carlo method. For both basal and secretory cells, the dose conversion coefficients (DCCs) for physical conditions of sleep, rest, light and heavy exercise, have been obtained for Chinese males and females for unattached progeny, and for attached progeny of diameters 0.02, 0.15, 0.25, 0.30 and 0.50 micron. For basal cells, the coefficients lie in the range 0.69-6.82 mGy/(Js/m3) or 8.7-86 mGy/WLM for unattached progeny and in the range 0.045-1.98 mGy/(Js/m3) or 0.57-25 mGy/WLM for attached progeny. The corresponding ranges for Caucasian males are 1.27-8.81 mGy/(Js/m3) or 16-111 mGy/WLM-1 and 0.05-2.30 mGy/(Js/m3) or 0.64-29 mGy/WLM. For secretory cells, the coefficients lie in the range 0.095-16.82 mGy/(Js/m3) (1.2-212 mGy/WLM) for unattached progeny and in the range 0.095-6.67 mGy/(Js/m3) (1.2-84 mGy/WLM) for attached progeny. The corresponding ranges for Caucasian males are 0.34-21.51 mGy/(Js/m3) (4.3-271 mGy/WLM) and 0.1-7.78 mGy/(Js/m3) (1.3-98 mGy/WLM). The overall DCCs calculated for a typical home environment are 0.59 and 0.52 mSv/(Js/m3) (7.4 and 6.5 mSv/WLM) for Chinese males and females, respectively, which are 80 and 70% of the value, 0.73 mSv/(Js/m3) (9.2 mSv/WLM), for Caucasian males.

Activities of Daily Living↗

PubMed2001

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 3.3 cm s(-1) for home exposure and 4.6 cm s(-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 mSv WL M(-1)) with the size of radon progeny from 1 to 1000 nm. 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.

Bronchi↗

PubMed2001

Alpha hit frequency due to radon decay products in human lung cells.

PURPOSE: To calculate the hit probabilities by alpha-particles emitted by radon progeny for basal and secretory cell nuclei in the epithelium of the human tracheobronchial tree. MATERIALS AND METHODS: The equilibrium activities on the surface of airway tubes were calculated using the ICRP66 model. The stopping-power and ranges of alpha-particles in tissue were adopted from ICRU49. A semi-analytical method for determining the alpha-particle fluence rate in tissue was applied. The distributions of secretory and basal cells throughout the tracheobronchial tree were as given by Mercer et al. (1991). RESULTS: The probability to hit basal cell nuclei is three-to-four times smaller than for secretory cell nuclei in the bronchial region (BB). However, the total number of traversed basal cell nuclei is greater because of the larger volume abundance of basal cells in BB. The total number of secretory cell nuclei hit in the bronchiolar region (bb) is larger than that in BB because the volume abundance of secretory cells in bb is larger than that in BB. CONCLUSIONS: Basal cells are more sensitive to alpha-radiation than secretory cells. This finding is based on the analysis of the relative number of cell hits and the relative frequencies of lung cancer induction in BB and bb.

Aerosols↗

PubMed2001

Absorbed fraction and dose conversion coefficients of alpha particles for radon dosimetry.

The sensitivity to different relevant parameters of the absorbed fraction of alpha particles emitted from the 222Rn chain in sensitive cells of the tracheo-bronchial tree have been investigated. The structure of the airway wall given by ICRP (ICRP66) has been adopted and employed in the present calculations. The source thickness (mucous gel and sol + cilia), target layer thickness and the depth of the sensitive layers have been varied within reasonable ranges around the default values recommended by ICRP66. The results have shown that the depth of the sensitive layers is the most important parameter in calculating the absorbed fraction. In addition, dose conversion coefficients were calculated and presented along with the absorbed fractions.

Alpha Particles↗