Sergei A. Paschuk

Computerized tomography with high-energy proton beams: tomographic image reconstruction from computer-simulated data

The use of protons instead of X-rays for computerized tomography (CT) studies has potential advantages, especially for medical applications in proton treatment planning. However, the spatial resolution of proton CT is limited by multiple Coulomb scattering (MCS). We used the Monte Carlo simulation tool GEANT4 to study the resolution achievable with different experimental arrangements of a proton CT scanner. The passage of a parallel 200MeV proton beam through a virtual cylindrical aluminum phantom with 50mm external diameter was simulated. In our study, the phantom contained a set of cylindrical holes with diameters ranging from 4mm to 0.5mm. The GEANT4 simulation consisted of a series of 180 projections at 2 degree intervals with 350 proton track histories for each one. The filtered back projection algorithm was used to reconstruct a 2D tomographic image of phantom.

Evaluation of Escherichia coli cells damages induced by ultraviolet and proton beam radiation

Prokaryote cells were exposed to ultra violet (UVc) radiation and to proton beams in order for the induced effects to be studied. Morphological and physiological alterations occurred in Escherichia coli (E. coli) cells exposed to the beams were investigated. The measurements using UVc radiation were made at the Biology Department of CEFET-PR while the measurements using proton beams were made at the Pelletron Accelerator

Studies of electrical properties of polyaniline irradiated by X-rays

Recent development and studies of physical and chemical properties of the conducting polymers have been calling the interest of many scientists. Among this group of materials, the polyaniline (PANI) deserves special attention because of its high chemical and thermal stability under normal conditions, simple process of polymerization and low cost. This polymer is also known due to its strongly pronounced and well studied electrochemical characteristics. In the present work, the variations of the electrical resistance of polyaniline caused by X-rays radiation have been studied. The polymer has been synthesized by electrochemical method in stainless steel and graphite electrodes. The data concerning the electrical resistance of PANI were measured just after the synthesis. This has been performed in the water solution of sulfuric acid within monomer of aniline where the polyaniline has been submitted to the applied voltages in the range from 200mV to 600mV. Polymeric samples have been irradiated using the X-rays with the energy 50keV and 100keV. After the irradiation, the electrical measurements have been repeated. The whole experimental procedure was performed several times. The obtained results have clearly shown the potential of polyaniline as a dose sensitive material that could be applied as a radiation sensor.

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.

GEANT4 Tuning For pCT Development

Proton beams in medical applications deal with relatively thick targets like the human head or trunk. Thus, the fidelity of proton computed tomography (pCT) simulations as a tool for proton therapy planning depends in the general case on the accuracy of results obtained for the proton interaction with thick absorbers. GEANT4 simulations of proton energy spectra after passing thick absorbers do not agree well with existing experimental data, as showed previously. Moreover, the spectra simulated for the Bethe‐Bloch domain showed an unexpected sensitivity to the choice of low‐energy electromagnetic models during the code execution. These observations were done with the GEANT4 version 8.2 during our simulations for pCT. This work describes in more details the simulations of the proton passage through aluminum absorbers with varied thickness. The simulations were done by modifying only the geometry in the Hadrontherapy Example, and for all available choices of the Electromagnetic Physics Models. As the most pr...

Reduced calibration curve for proton computed tomography

The pCT deals with relatively thick targets like the human head or trunk. Thus, the fidelity of pCT as a tool for proton therapy planning depends on the accuracy of physical formulas used for proton interaction with thick absorbers. Although the actual overall accuracy of the proton stopping power in the Bethe‐Bloch domain is about 1%, the analytical calculations and the Monte Carlo simulations with codes like TRIM/SRIM, MCNPX and GEANT4 do not agreed with each other. A tentative to validate the codes against experimental data for thick absorbers bring some difficulties: only a few data is available and the existing data sets have been acquired at different initial proton energies, and for different absorber materials. In this work we compare the results of our Monte Carlo simulations with existing experimental data in terms of reduced calibration curve, i.e. the range—energy dependence normalized on the range scale by the full projected CSDA range for given initial proton energy in a given material, take...

222Rn Measurements at Federal University of Technology (UTFPR, Curitiba, PR, Brazil)

Numerous studies and reports indicate that the indoor radon inhalation by humans has to be considered as the main source of radiological hazard and probably the second most important cause of lung cancer after that of smoking. During the last decades, many countries have put considerable efforts into direct measurements and monitoring of 222Rn and its progeny exposure, as well as 222Rn concentration mapping. Present measurements were performed with an aim to study possible correlation between used construction materials and 222Rn indoor concentration levels. For this purpose, 50 Lexan track detectors were exposed in the air (indoor as well as outdoor) during two months (June and July) within the central region of Curitiba and Campo Largo (Parana St., Brazil). Since this period of the year is usually rather cold in the South of Brazil, exposition time was chosen to prevent possible saturation of alpha tracks. The second step of measurements was performed during the months of November, December and January,...