Valeriy Denyak

Activity measurements of radon from construction materials

This work presents the results of radon concentration measurements of construction materials used in the Brazilian industry, such as clay (red) bricks and concrete blocks. The measurements focused on the detection of indoor radon activity during different construction stages and the analysis of radionuclides present in the construction materials. For this purpose, sealed chambers with internal dimensions of approximately 60×60×60 cm3 were built within a protected and isolated laboratory environment, and stable air humidity and temperature levels were maintained. These chambers were also used for radon emanation reduction tests. The chambers were built in four major stages: (1) assembly of the walls using clay (red) bricks, concrete blocks, and mortar; (2) installation of plaster; (3) finishing of wall surface using lime; and (4) insulation of wall surface and finishing using paint. Radon measurements were performed using polycarbonate etched track detectors. By comparing the three layers applied to the masonry walls, it was concluded that only the last step (wall painting using acrylic varnish) reduced the radon emanation, by a factor of approximately 2. Samples of the construction materials (clay bricks and concrete blocks) were ground, homogenized, and subjected to gamma-ray spectrometry analysis to evaluate the activity concentrations of 226Ra, 232Th and 40K. The values for the index of the activity concentration (I), radium equivalent activity (Raeq), and external hazard index (Hext) showed that these construction materials could be used without restrictions or concern about the equivalent dose limit (1 mSv/year).

Evaluation of Fetal Dose in Breast Radiotherapy With Shielding and Wedges

The fetus may be seriously affected by the peripheral dose when a pregnant woman undergoes breast radiotherapy. To quantify this dose, a humanoid phantom was irradiated at the left breast, simulating breast radiotherapy. The phantom, consisting of an adapted manikin (with internal and external materials having densities close to that of water), was irradiated in a 6-MeV X-ray linear accelerator (Clinac 600CD). A shield of blocks and lead slabs was placed around the abdominal region of the phantom. Two types of wedges were used to modulate the beam: a physical wedge and the enhanced dynamic wedge (EDW), both with 30° angulation. Using a cylindrical ionization chamber of 0.6 cm 3 positioned in the phantoms fetal region, at the end of breast treatment, the peripheral doses were 3.90-48.67 cGy with the physical wedge and 1.75-13.78 cGy with the EDW. The doses were 3.5 times greater when the physical wedge was used due to scattering by its attenuator material and the increase in the leakage radiation intensity. The use of a shield around the abdominal region of the phantom and the use of the EDW during simulation of the treatment reduced the peripheral doses to tolerable limits from ICRP and AAPM.

Validation of Geant4 on Proton Transportation for Thick Absorbers: Study Based on Tschalär Experimental Data

Imaging techniques using protons as incident particles are currently being developed to substitute X-ray computer tomography and nuclear magnetic resonance methods in proton therapy. They deal with relatively thick targets, like the human head or trunk, where protons lose a significant part of their energy, however, they have enough energy to exit the target. The physical quantities important in proton imaging are kinetic energy, angle and coordinates of emerging proton from an absorber material. In recent times, many research groups use the Geant4 toolkit to simulate proton imaging devices. Most of the available publications about validation of Geant4 models are for thin or thick absorbers (Bragg Peak studies), that are not consistent with the contour conditions applied to proton imaging. The main objective of this work is to evaluate the kinetic energy spectrum for protons emerging from homogeneous absorbers slabs comparing it to the experimental results published by Tschalär and Maccabee, in 1970. Different models (standard and detailed) available on Geant4 (version 9.6.p03) are explored taking into account its accuracy and computational performance. This paper presents a validation for protons with incident kinetic energies of 19.68 MeV and 49.10 MeV. The validation results from the emerging protons kinetic energy spectra show that: (i) there are differences between the reference data and the data produced by different processes evoked for transportation and (ii) the validation energies are sensitive to sub-shell processes.

Evaluation of Geant4 to describe proton transportation for thick absorbers

Imaging techniques using protons are actively being developed currently to substitute X-ray computer tomography and nuclear magnetic resonance method in proton therapy. They deals with relatively thick targets like the human head or trunk where protons lose the major part of their energy, however they having enough energy to exit the target. The physical quantities important in proton imaging are proton exit energy, angle and coordinates. Nowadays many research groups are using The Geant4 toolkit for the development of proton imaging devices. However the most of available publications about validation of the Geant4 models are or for thin absorbers, or for energy deposition of completely absorbed protons (Bragg Peak), what are not important characteristics in proton imaging. The main objective of this work is to validate different models available on Geant4 (version 9.6.p03) taking into account its accuracy and computational performance from the viewpoint of proton imaging. This paper presents the comparison against experimental data published by Tschalär and Maccabee (for incident kinetic energies for protons of 19.68 MeV and 49.10 MeV). The results show that for the validation energies the spectra of the kinetic energy of the emerging protons: (i) there are differences between the validation and the different processes invoked for transportation and (ii) the validation energies are sensitive to sub-shell processes.

Validation of Geant4 for scattered spectrum from pediatric exams for dosimetry of occupational workers applied to radiological protection

Fluoroscopic barium meal (BM) studies are largely used around the world and very common to be performed in children. The medical and occupational exposures are important parameters that need to be investigated to evaluate the radiological effects. Calibration of the dosimeter used for exposure measurement is usually done with primary X-ray beam. The difference in energy spectra of primary and scattered radiation can influence obtained results. The main objective of this work is to evaluate the X-ray scattered spectra by different pediatric phantoms (simulation of patients subjected to BM procedures) to calculate an energy correction factor to the absorbed energy by the thermoluminescent dosimeters (TLD). To perform this evaluation, the TLDs were positioned over three areas in two occupational workers eyes, thyroid and hands. The Geant4 toolkit was used to define the spectra that reached TLDs and made possible to correct entrance surface air kerma. The present work was developed in two stages: (i) evaluation of scattered spectra by different standard phantoms (newborn, 1 year old, 5 years old and 10 years old); (ii) definition of the energy correction factor to the absorbed energy by each TLD. The results of this work show that Geant4 is a good toolkit to these analysis making possible to generate a correction factor considering a primary spectrum of 60 keV.

MONITORAMENTO DA RADIOATIVIDADE ALFA RELACIONADA AO RADÔNIO-222 EM ÁGUAS DE POÇOS DA REGIÃO METROPOLITANA DE CURITIBA-PR

This research objective was to assess the level of randon-222 concentration in well water of the metropolitan region of Curitiba, Parana. Current work presents the results of indoor 222Rn activity ground water samples from artesian wells from aquifers of the region. The studies of radon activity in water were performed using the radon detector AlphaGUARD. The calculations of initial radon activity in water were done considering the 222Rn decay correction as well as equilibrium level of 222Rn and 226Ra observed after 30 days of measurements. Obtained results show that about 70% of measured activity levels of 222Rn are higher than the recommended value of 11.1 Bq.L-1, which represent the risk for the human health associated with this radionuclide. The case study showed that previous measurements of radon are recommended for a construction project is implemented. In this case, it is observed that the radon concentrations decrease about 56% in the first water tank and 83% in the second water tank over the well. This fact shows that the actions for mitigation of radon are viable and do not require major modifications to the usual systems of construction.

Comparison of Geant4 version 9.3 simulations with experimental results from a prototype proton CT scanner

Charged particle interactions with matter have been continuously studied by simulations based on the Monte Carlo method. In particular, the Geant4 toolkit allows to develop and test new technologies by computer simulations. A proton computed tomography (pCT) prototype has been developed at the Lorna Linda University Medical Center (LLUMC), California, in collaboration with Northern Illinois University and the UC Santa Cruz. In order to evaluate the performance of the Geant4 version 9.3 configured to simulate this prototype, two polyethylene phantoms (PEA D) with 150 mm diameter and acrylic core were constructed. Each phantom was imaged with 10 projections by rotating the phantom in steps of 36, using a 200 MeV proton cone beam. The characteristics of the prototype and phantoms were modeled in Geant4. A comparison of the experimental data and simulated projections were performed and will be presented.

Comparison of the GEANT4 releases 8.2 and 9.2 in terms of a pCT reduced calibration curve

The GEANT4 simulations are essential for the development of medical tomography with proton beams — pCT. In the case of thin absorbers the latest releases of GEANT4 generate very similar final spectra which agree well with the results of other popular Monte Carlo codes like TRIM/SRIM, or MCNPX. For thick absorbers, however, the disagreements became evident. In a part, these disagreements are due to the known contradictions in the NIST PSTAR and SRIM reference data. Therefore, it is interesting to compare the GEANT4 results with each other, with experiment, and with diverse code results in a reduced form, which is free from this kind of doubts. In this work such comparison is done within the Reduced Calibration Curve concept elaborated for the proton beam tomography.

Particle Initial Energy Choice in Proton Computed Tomography for Medical Purposes

In the earliest works devoted to proton computed tomography (pCT) it was shown that the advantage of pCT image reconstruction appears when the energy is chosen as small as possible but sufficient to pass the object. At the same time there are two effects that work on the contrary, increasing the necessary irradiation dose with decreasing proton energy. In this work the radiation dose dependence from the proton initial energy was studded using analytical formulas and computer simulation. The carried out investigation shows that the irradiation dose practically does not depend on the proton energy except at the small energy region very close to the minimal energy.