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Biomedical subjects

K N Yu

Publications and source records attributed to K N Yu.

At least 19 recordsLinked to original sources
PubMed2007

Killing of target cells due to radon progeny in the human lung.

The dose conversion coefficient (DCC) is used to assess the risk due to inhaled radon progeny in the human lung. The present work uses the microdosimetric approach and determines the linear energy transfer in the target cell nuclei. Killing of target cells was also taken into account through an effect-specific track length model. To focus on the relevant part of the absorbed dose in the cell nuclei, the absorbed dose, which causes cell-killing is discarded in the final calculations of the DCC. Following this approach, the calculated DCC has become 3.4 mSv WLM(-1) which is very close to the epidemiologically derived value of approximately 4 mSv WLM(-1).

Aerosols↗
PubMed2006

Alpha-particle radiobiological experiments using thin CR-39 detectors.

The present paper studied the feasibility of applying comet assay to evaluate the DNA damage in individual HeLa cervix cancer cells after alpha-particle irradiation. We prepared thin CR-39 detectors (<20 microm) as cell-culture substrates, with UV irradiation to shorten the track formation time. After irradiation of the HeLa cells by alpha particles, the tracks on the underside of the CR-39 detector were developed by chemical etching in (while floating on) a 14 N KOH solution at 37 degrees C. Comet assay was then applied. Diffusion of DNA out of the cells could be generally observed from the images of stained DNA. The alpha-particle tracks corresponding to the comets developed on the underside of the CR-39 detectors could also be observed by just changing the focal plane of the confocal microscope.

Alpha Particles↗
PubMed2006

Derivation of V function for LR 115 SSNTD from its partial sensitivity to 222Rn and its short-lived progeny.

Solid-state nuclear track detectors (SSNTDs) have been widely applied for measurements of environmental concentrations of 222Rn and its progeny. The V function for an SSNTD is important for understanding the track development in the SSNTD as well as for real life applications. The partial sensitivity rhoi of the LR 115 detector applied in the bare mode to 222Rn and its short-lived progeny is related to the equilibrium factor F through the proxy equilibrium factor Fp. On the other hand, rhoi is also dependent on the removed active layer thickness during chemical etching, which is related to the V function for the LR 115 detector. In the present paper, the experimentally obtained rhoi values of the LR 115 detector for different removed active layer thickness are used to derive the V function for the LR 115 SSNTD, which took the form of the Durrani--Green's function, i.e., [formula: see text] , with the best-fitted constants as a1=14.23; a2=0.48; a3=5.9 and a4=0.077 (a5=1).

Alpha Particles↗
PubMed2006

Derivation of V function for LR 115 SSNTD from its sensitivity to 220Rn in a diffusion chamber.

The sensitivity of the LR 115 detector inside a diffusion chamber to (220)Rn gas concentration is dependent on the removed active layer thickness during chemical etching. This dependence is related to the V function for the LR 115 detector (where V is the ratio between the track etch velocity V(t) and the bulk etch velocity V(b)) and the geometry of the diffusion chamber. The present paper presents the experimentally determined relationship between the sensitivity of the LR 115 detector inside a Karlsruhe diffusion chamber (determined from the number of etched tracks completely penetrating the active cellulose nitrate layer) and the removed active layer thickness. These data were used to derive the V function for the LR 115 detector, which took the functional form of the Durrani-Green's function, i.e., V=1+((a1e-)(a2R+a3e(-a)4R))(1(-e)(-a5R)), with the best-fitted constants as a(1)=14.50, a(2)=0.50, a(3)=3.9 and a(4)=0.066.

Journal Article↗
PubMed2006

Comparison of dose conversion factors for radon progeny from the ICRP 66 regional model and an airway tube model of tracheo-bronchial tree.

Current epidemiological approaches to radon dosimetry yield a dose conversion factor (DCF) of 4 mSv WLM(-1) while the dosimetric approaches give a value closer to 13 mSv WLM(-1). The present study investigated whether the application of compartment models for the bronchial (BB) and bronchiolar (bb) regions, rather than more anatomically realistic airway tube models, has brought the dosimetric DCF to the higher values. The airway tube model of the tracheo-bronchial tree was used to calculate the effective dose per unit radon exposure. All other elements of the human respiratory tract from the reports of the ICRP or NRC were adopted. A dosimetric derivation of the radon DCF using the airway tube model yielded a value of 14.2 mSv WLM(-1). This value is slightly larger than, but not significantly different from, the result obtained through the ICRP 66 approach. It is concluded that utilization of the airway tube model instead of the regional ICRP 66 compartmental model cannot reconcile the gap between dose conversion factors derived from epidemiological and dosimetric approaches.

Air Pollutants, Radioactive↗
PubMed2006

Absorbed dose in target cell nuclei and dose conversion coefficient of radon progeny in the human lung.

To calculate the absorbed dose in the human lung due to inhaled radon progeny, ICRP focussed on the layers containing the target cells, i.e., the basal and secretory cells. Such an approach did not consider details of the sensitive cells in the layers. The present work uses the microdosimetric approach and determines the absorbed alpha-particle energy in non-spherical nuclei of target cells (basal and secretory cells). The absorbed energy for alpha particles emitted by radon progeny in the human respiratory tract was calculated in basal- and secretory-cell nuclei, assuming conical and ellipsoidal forms for these cells. Distributions of specific energy for different combinations of alpha-particle sources, energies and targets are calculated and shown. The dose conversion coefficient for radon progeny is reduced for about 2mSv/WLM when conical and ellipsoidal cell nuclei are considered instead of the layers. While changes in the geometry of secretory-cell nuclei do not have significant effects on their absorbed dose, changes from spherical to conical basal-cell nuclei have significantly reduced their absorbed dose from approximately 4 to approximately 3mGy/WLM. This is expected because basal cells are situated close to the end of the range of 6MeV alpha particles. This also underlines the significance of better and more precise information on targets in the T-B tree. A further change in the dose conversion coefficient can be achieved if a different weighting scheme is adopted for the doses for the cells. The results demonstrate the necessity for better information on the target cells for more accurate dosimetry for radon progeny.

Humans↗
PubMed2006

Assessment of environmental radon hazard using human respiratory tract models.

Radon is a natural radioactive gas derived from geological materials. It has been estimated that about half of the total effective dose received by human beings from all sources of ionizing radiation is attributed to 222Rn and its short-lived progeny. In this paper, the use of human respiratory tract models to assess the health hazard from environmental radon is reviewed. A short history of dosimetric models for the human respiratory tract from the International Commission on Radiological Protection (ICRP) is first presented. The most important features of the newest model published by ICRP in 1994 (as ICRP Publication 66) are then described, including the morphometric model, physiological parameters, radiation biology, deposition of aerosols, clearance model and dose weighting. Comparison between different morphometric models and comparison between different deposition models are then given. Finally, the significance of various parameters in the lung model is discussed, including aerosol parameters, subject related parameters, target and cell related parameters, and parameters that define the absorption of radon from the lungs to blood. Dosimetric calculations gave a dose conversion coefficient of 15 mSv/WLM, which is higher than the value 5 mSv/WLM derived from epidemiological studies. ICRP stated that dosimetric models should only be used for comparison of doses in the human lungs resulted from different exposure conditions.

Aerosols↗
PubMed2006

Study of scattered photons from the collimator system of Leksell Gamma Knife using the EGS4 Monte Carlo code.

In the algorithm of Leksell GAMMAPLAN (the treatment planning software of Leksell Gamma Knife), scattered photons from the collimator system are presumed to have negligible effects on the Gamma Knife dosimetry. In this study, we used the EGS4 Monte Carlo (MC) technique to study the scattered photons coming out of the single beam channel of Leksell Gamma Knife. The PRESTA (Parameter Reduced Electron-Step Transport Algorithm) version of the EGS4 (Electron Gamma Shower version 4) MC computer code was employed. We simulated the single beam channel of Leksell Gamma Knife with the full geometry. Primary photons were sampled from within the 60Co source and radiated isotropically in a solid angle of 4pi. The percentages of scattered photons within all photons reaching the phantom space using different collimators were calculated with an average value of 15%. However, this significant amount of scattered photons contributes negligible effects to single beam dose profiles for different collimators. Output spectra were calculated for the four different collimators. To increase the efficiency of simulation by decreasing the semiaperture angle of the beam channel or the solid angle of the initial directions of primary photons will underestimate the scattered component of the photon fluence. The generated backscattered photons from within the 60Co source and the beam channel also contribute to the output spectra.

Computer Simulation↗
PubMed2006

Rotating and static sources for gamma knife radiosurgery systems: Monte Carlo studies.

Rotating gamma systems (RGSs), GammaART-6000, and its Chinese equivalents, such as OUR and MASEP, etc., are new radiosurgery systems that use rotating 60Co sources instead of the 201 static sources (Leksell gamma knife, LGK). The rotating sources of RGSs simulate an infinite number of beams and promote extremely high target to surface dose ratios. However, the results of Monte Carlo in this study shows that RGS variants (modeled as having the same latitude angles, source to focus distance, and the distance from the source to the end of the collimator as the LGK) have smaller beam profile penumbra in the z direction, while LGK has smaller penumbra in the x and y directions. The differences are more significant in using larger collimators.

Cobalt Radioisotopes↗
PubMed2005

Are radon gas measurements adequate for epidemiological studies and case control studies of radon-induced lung cancer?

The lung dose derived from radon is not attributed to the radon gas itself, but instead to its short-lived progeny. However, in many epidemiological studies as well as in case control studies of the radon risk, the excess number of cancers are related to the radon gas exposure, and not to the radon progeny exposure. A justification for such an approach has resorted to the assumption that there is self-compensation between the radiation doses from the unattached and attached fractions. In the present study, we used the Jacobi model to calculate the radon progeny concentrations in a room by varying the attachment rate and then calculated the resulting lung dose. It was found that self-compensation was not fully realised, and the effective dose can vary by a factor up to approximately 2 for the same radon gas concentration. In conclusion, the radon gas concentration alone does not provide adequate information on the effective dose.

Algorithms↗
PubMed2004

Theoretical basis for long-term measurements of equilibrium factors using LR 115 detectors.

In this paper, we propose a method to determine the equilibrium factor using a bare LR 115 detector. The partial sensitivities rhoi of the LR 115 detector to 222Rn and its alpha-emitting short-lived progeny, 218Po and 214Po, were investigated. We first determined the distributions of lengths of major and minor axes of the perforated alpha tracks in the LR 115 detector produced by 222Rn, 218Po and 214Po through Monte Carlo simulations. The track parameters were calculated using a track development model with a published V function, by assuming a removed active layer of 6.54 microm. The distributions determined for different alpha emitters were found to completely overlap with one another. This implied equality of partial sensitivities for radon and its progeny, which was also confirmed through analytical considerations. Equality of partial sensitivities makes possible convenient measurements of the proxy equilibrium factor Fp, which is defined in the present work as (F1+F3) and is equal to the ratio between the sum of concentrations of the two alpha emitting radon progeny (218Po+214Po) to the concentration of radon gas (222Rn). In particular, we have found Fp = (rho/rhoitC0)-1, where rho (track/m2) is the total track density on the detector, rhoi = 0.288 x 10(-2) m, t is the exposure time and C0 (Bq/m3) is the concentration of 222Rn. If C0 is known (e.g. from a separate measurement), we can obtain Fp. The proxy equilibrium factor Fp is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor.

Journal Article↗
PubMed2004

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.

Adult↗
PubMed2004

Measurement of parameters of tracks in CR-39 detector from replicas.

In determining the etched track rate in solid-state nuclear track detectors, track lengths should be determined accurately. A method based on surface profilometry is proposed to determine the track lengths in CR-39 detectors through measurements of their replicas. Tracks from alpha particles with an incident energy of 4 MeV have been chosen to demonstrate the method. After irradiation and chemical etching, resin replicas were made from the tracks, of which the heights were measured by the Form Talysurf PGI Profilometer. The results showed that the surface of the replicas were smooth and the heights of the replicas were uniform, so the replicating fluid should have filled the tracks completely and the replicas truly reflected the dimensions of the tracks. The heights of the replicas were conveniently determined from the lateral view of the replicas generated by the Form Talysurf PGI Profilometer.

Alpha Particles↗
PubMed2004

Dose enhancement close to platinum implants for the 4, 6, and 10 MV stereotactic radiosurgery.

Three photon interaction processes, namely, the photoelectric effect, Compton effect, and pair production, can occur when materials with high atomic numbers are irradiated by the high- and low-energy bremsstrahlung photons from a linear accelerator. A dose enhancement, due to the photoelectric effect and pair production, near targets with platinum implants (with a high atomic number) in radiosurgery cannot be predicted by the XKnife radiosurgery treatment planning system. In the present work, Monte Carlo simulations using PRESTA EGS4 were employed to investigate the resulting dose enhancements from 4, 6, and 10 MV energies commonly used in the stereotactic radiosurgery system. Dose enhancements from 32% to 68% were observed close to the platinum implant for the above energies when using a 12.5 mm collimator. Comparatively higher dose enhancements were observed when using smaller collimators. It was found that this dose enhancement increased with beam energy but decreased as beam size increased.

Algorithms↗
PubMed2003

Absorbed fraction of alpha-particles emitted in bifurcation regions of the human tracheo-bronchial tree.

A model for bifurcation regions of the human tracheo-bronchial tree was developed. Equations for the surfaces are given to enable calculations of doses from alpha-particles emitted in these regions. It has been found that a bifurcation region is well approximated by a quasi-ellipsoid. The absorbed fractions of alpha-particles emitted in bifurcation regions were calculated by the Monte Carlo method. The average absorbed fraction under the bifurcation geometry is close to that found under the cylindrical geometry in the bronchial region. In the bronchiolar region, the absorbed fractions under the bifurcation geometry are up to 20% larger than those under the cylindrical geometry.

Air Pollutants, Radioactive↗