Absorbed Dose Estimation by Monte Carlo Simulation Conversion Factor of Physical Dosimeters (original) (raw)
Related papers
2012
In our world, nuclear accident is unavoidable. This means that we are under radiation risk all the time. Therefore, you should determine the ionized atoms (absorbed dose) punctually and as fast as possible to deal properly with victims in the triage process. The present study attempts to determine the absorbed dose generated in femur bone that utilized femur phantom (Health Physics Society N13.32) after different energy levels (30 keV to 10 MeV) relying on the numerical simulation of Monte Carlo N-Particle (MCNP)-5. The results showed the gradual reduction of Kerma air free values with the increase of energy from 30 to 100 keV, after a dramatic increase was noticed up to 10 MeV. The behaviour of the conversion factor illustrated the inverse relation with increment of energy. The first value was obtained at 30 keV (0.0368 Gy/Gy) and remarkable decrease was observed up to 150 keV (0.0245 Gy/Gy). The conversion factor remains almost constant between 200 and 800 keV and dramatic depress...
A B S T R A C T One of the main criteria that must be held in Total Body Irradiation (TBI) is the uniformity of dose in the body. In TBI procedures the certification that the prescribed doses are absorbed in organs is made with dosimeters positioned on the patient skin. In this work, we modelled TBI scenarios in the MCNPX code to estimate the entrance dose rate in the skin for comparison and validation of simulations with experimental measurements from literature. Dose rates were estimated simulating an ionization chamber laterally positioned on thorax, abdomen, leg and thigh. Four exposure scenarios were simulated: ionization chamber (S1), TBI room (S2), and patient represented by hybrid phantom (S3) and water stylized phantom (S4) in sitting posture. The posture of the patient in experimental work was better represented by S4 compared with hybrid phantom, and this led to minimum and maximum percentage differences of 1.31% and 6.25% to experimental measurements for thorax and thigh regions, respectively. As for all simulations reported here the percentage differences in the estimated dose rates were less than 10%, we considered that the obtained results are consistent with experimental measurements and the modelled scenarios are suitable to estimate the absorbed dose in organs during TBI procedure.
—Monte Carlo codes are among the most used tools for calculations and simulations relating to medical physics and particularly for studies of low dose medical applications. The results, presented in this paper, were focused on the optimization of a medical phantom for mapping the absorbed doses produced by ionizing radiation. The cobalt 60 irradiator of the CNSTN (the National Centre for Nuclear Science and Technology) served as the experimental validation platform for the present study. Monte-Carlo modeling of the irradiator was carried out with Geant4 tool. Part of dose deposition results, obtained with this model, has been validated using as reference previous experimental data, performed on the same irradiator. The same Geant4 model was then adapted to our study case, with the development of a more specific configuration, suitable for the diagnosis of the effects induced by gamma radiation beams at different energies. The distribution study of doses produced by these photons, inside a water filled phantom, was thus realized. The numerical results obtained, with the Geant4 model, show variable behaviours according to the studied energies. An analytical model is then proposed, for the prediction of these dose distributions.
Radiation Measurements, 2015
Absorbed doses to fingernails and organs were calculated for a set of homogenous external gamma-ray irradiation geometries in air. The doses were obtained by stochastic modeling of the ionizing particle transport (Monte Carlo method) for a mathematical human phantom with arms and hands placed loosely along the sides of the body. The resulting dose conversion factors for absorbed doses in fingernails can be used to assess the dose distribution and magnitude in practical dose reconstruction problems. For purposes of estimating dose in a large population exposed to radiation in order to triage people for treatment of acute radiation syndrome, the calculated data for a range of energies having a width of from 0.05 to 3.5 MeV were used to convert absorbed doses in fingernails to corresponding doses in organs and the whole body as well as the effective dose. Doses were assessed based on assumed rates of radioactive fallout at different time periods following a nuclear explosion.
Physics in Medicine and Biology, 2003
Our aim in this work was to investigate the methodology used in the determination of the entrance surface dose (ESD) in diagnostic radiology. In kV x-rays for low-energy photons (tube potential up to 160 kV, HVL: 1-8 mm Al), the ESD is based on the use of the ratio of mass-energy absorption coefficients and backscatter factors. A full simulation of the photon and electron transport in a kilovoltage x-ray unit, using the Monte Carlo code BEAM/EGS4, was performed to obtain an accurate beam phase space for use in dose calculation. The modelled phase space was experimentally validated for the beam qualities (measured HVL: 3.3 mm Al-2.2 mm Cu) and showed good agreement between calculated and measured HVLs, air kerma and relative dose distributions. We have computed the conversion factors from air kerma to water or soft tissue absorbed dose at the surface of a phantom for beam qualities (HVL: 3.3-8.35 mm Al). The same model was also used to calculate the ESD in water and in soft tissue for the low-energy photon range considered. The results show that the numerical differences between the air kerma and the water kerma based backscatter factors are insignificant. The same conclusion was reached for the (µ en /ρ) ratios, for soft tissue to air, evaluated using either the primary photon spectra or the spectra at the surface of a phantom. Furthermore, the good agreement obtained for the computation of the conversion factors with a full BEAM/EGS4 model confirms the previous studies which are based on different sources for the spectral distribution and different beam geometries (pencil beam or point source assumptions). On the other hand, the ESD in water or soft tissue is well described either with the B air or the B w formalism. Conversion factors from air kerma to ESD in these media are proposed in this work for several beam qualities in diagnostic radiology.
Comparison of Methods and Systems in Internal Radiation Dosimetry
Biomedical Journal of Scientific & Technical Research, 2021
This different internal dosimetry methods were developed for the purpose of radioprotection, and radiation safety to minimize the risk of the effects of ionizing radiation on the people. The current method for calculating dose was proposed by the ICRP [1-4]. Internal dosimetry modalities or methods are used when a radioactive material enters the body by different routes inhalation, ingestion, absorption, injection on different circumstances either by breathing, eating, or drinking respectively, contaminated air, fluids foods and wounds. These occur in different occasions, either occupational or accidentally. In this course class paper, we describe the various mathematical models for calculating the absorbed dose by diverse organs of the body.
Journal of Nuclear Science and Technology, 2012
A group of Monte Carlo simulations has been performed for external neutron dosimetry calculation based on a whole-body mathematical model. The Chinese mathematical phantom (CMP) is a mathematical human body model developed based on methods of ORNL (Oak ridge National Laboratory) mathematical phantom series (OMPS), and data from Chinese reference man and reference Asian man. Fluence-to-absorbed dose conversion coefficients of 24 organs and tissues for monoenergetic neutron beams ranging from 10 79 to 10 2 MeV were calculated using the Monte Carlo code MCNPX. Irradiation conditions include anterior-posterior, posterior-anterior, right lateral, left lateral, rotational, and isotropic geometries. Results for the different organs are compared with those recommended in International Commission of Radiological Protection (ICRP) publication 74 and results obtained based on the visible Chinese human (VCH) phantom. Overall the consistency among the three sets of data was observed, but significant deviations up to 30-50% were also found in the AP, PA and lateral irradiation conditions. Since CMP represents the Chinese population, this work is helpful as a reference to investigate the difference of the neutron induced organ doses due to the anatomical variation between the Chinese and the Caucasians, and that between the average population and an individual.
Health physics, 2017
Reference phantoms are widely applied to evaluate the radiation dose for external exposure. However, the frequently used reference phantoms are based on Caucasians. Dose estimation for Asians using a Caucasian phantom can result in significant errors. This study recruited 40 volunteers whose body sizes are close to the average Taiwanese population. Magnetic resonance imaging was performed to obtain the organ volume for construction of the Taiwanese reference man (TRM) and Taiwanese reference woman (TRW). The dose conversion coefficients (DCC) resulting from photo beams in anterior-posterior, posterior-anterior, right-lateral, left-lateral, and isotropic irradiation geometries were estimated. In the anterior-posterior geometry, the mean DCC differences among organs between the TRM and ORNL phantom at 0.1, 1, and 10 MeV were 7.3%, 5.8%, and 5.2%, respectively. For the TRW, the mean differences from the ORNL phantom at the three energies were 10.6%, 7.4%, and 8.3%. The DCCs of the Taiw...
A new approach for the calculation of critical organ dose in nuclear medicine applications
Applied Radiation and Isotopes, 2005
The geometrical factor that is calculated to keep in mind the radiation source and detector position is rather frequently used in radiation measuring and calculating methods. In this study, using the geometrical factor is intended to suggest a new model to measure the absorbed dose in nuclear medicine applications. Therefore, the source and target organ's geometries are accepted to be disc and parallel to each other. In this manner, a mathematical model for the geometry of these discs is proposed and a disc-disc geometry factor is calculated. Theoretical calculations have been carried out with the MIRD (medical internal absorbed dose) method, which is widely used to the absorbed dose calculations in nuclear medicine. Absorbed radiation dose is separately calculated for a target organ, which is the testis, with disc-disc geometry factor model and MIRD model. Both the results are compared and the results of disc-disc geometry factor model are shown to be harmonious and acceptable with the results of MIRD model. r
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
International standards and guidelines for calibrating high-dose dosimetry systems to be used in industrial radiation processing recommend that dose-rate effects on dosimeters be evaluated under conditions of use. This is important when the irradiation relies on highcurrent electron accelerators, which usually provide very high dose-rates. However, most dosimeter calibration facilities use low-intensity gamma radiation or low-current electron accelerators, which deliver comparatively low dose-rates. Because of issues of thermal conductivity and response, portable calorimeters cannot be practically used with high-current accelerators, where product conveyor speeds under an electron beam can exceed several meters per second and the calorimeter is not suitable for use with product handling systems. As an alternative, Monte Carlo calculations can give theoretical estimates of the absorbed dose in materials with flat or complex configurations such that the results are independent of dose-rate. Monte Carlo results can then be compared to experimental dose determinations to see whether dose-rate effects in the dosimeters are significant. A Monte Carlo code has been used in this study to calculate the absorbed doses in alanine film dosimeters supported by flat sheets of plywood irradiated with electrons using incident energies extending from 1.0 MeV to 10 MeV with beam currents up to 30 mA. The same process conditions have been used for dose determinations with high-current electron beams using low dose-rate gamma calibrated alanine film dosimeters. The close agreement between these calculations and the dosimeter determinations indicates that the response of this type of dosimeter system is independent of the dose-rate, and provides assurance that Monte Carlo calculations can yield results with sufficient accuracy for many industrial applications.