Dosimetry audit in radiotherapy centers in Serbia in 2013

U radu su predstavljeni rezultati provere apsorbovanih doza u vodi za Co-60 i visokoenergetske snopove fotona na linearnim akceleratorima postignute u radioterapijskim ustanovama u Srbiji u sklopu Programa IAEA/WHO TLD postal dose quality audit. Program je sproveden u februaru 2013. godine preko koordinatora za Srbiju – SSDL INN Vinča, Laboratorija „Zaštita“. U Programu su učestvovali radioterapijski centri iz Beograda, Sremske Kamenice, Kragujevca, Niša i Kladova. Program ima za cilj da se prati i po potrebi vrši revizija dozimetrijskih procedura u radioterapiji za procenu pacijentnih doza.The purpose of this paper is to present the results of TLD absorbed doses in water for Co-60 and high-energy photon beams on linacs in radiotherapy centers in Serbia in the framework of the IAEA/WHO TLD Postal Dose Quality Audit Program. This program was carried out in February 2013, coordinated by SSDL INN Vinča Laboratory for Radiation Protection - country coordinator for Serbia. Radiotherapy centers from Belgrade, Sremska Kamenica, Kragujevac, Nis and Kladovo took part in this program. The aim of the program is to follow and, if needed, audit dosimetry procedures for estimation of patient dose in radiotherapy treatment.XXVII Simpozijum Društva za zaštitu od zračenja Srbije i Crne Gore, Tara, 12-14. oktobar 2011

Gamma-ray irradiation and post-irradiation at room and elevated temperature response of pMOS dosimeters with thick gate oxides

Gamma-ray irradiation and post-irradiation response at room and elevated temperature have been studied for radiation sensitive pMOS transistors with gate oxide thickness of 100 and 400 nm, respectively. Their response was followed based on the changes in the threshold voltage shift which was estimated on the basis of transfer characteristics in saturation. The presence of radiation-induced fixed oxide traps and switching traps - which lead to a change in the threshold voltage - was estimated from the sub-threshold I-V curves, using the midgap technique. It was shown that fixed oxide traps have a dominant influence on the change in the threshold voltage shift during gamma-ray irradiation and annealing

Improvement possibilities of the I-V characteristics of PIN photodiodes damaged by gamma irradiation

This paper presents the behavior of PIN photodiodes after combined gamma and neutron irradiation. Different types of PIN photodiodes have been exposed first to gamma and then to neutron irradiation. I-V characteristics (current dependence on voltage) of photodiodes have been measured after each of these irradiations. It has been noted that the photocurrent level after the neutron irradiation is higher than before it, which is not consistent with the current theories about the effects of neutron radiation on semiconductors. In order to explain this behavior of the photodiodes, the Monte Carlo simulation of photon transport through the material has been used. It is proposed that a possible cause for current enhancement are defects in semiconductor created by gamma irradiation and effects of neutron irradiation on these defects. The results can be explained by an intercentre transfer of charge between defects in close proximity to each other. The aim of this paper is to investigate the improvement possibilities of the I-V characteristics of PIN photodiodes, and photodetectors in general, damaged by gamma irradiation. [Projekat Ministarstva nauke Republike Srbije, br. 171007

On the role of circular sections of quadric surfaces

As a part of new advanced course curriculum of Descriptive geometry, in the Faculty of Civil engineering, creative 3D modeling of specific structures is included. These structures, inspired by contemporary architecture achievements, relay on quadric surfaces (quadrics). Here, student's knowledge concerning properties of the quadrics: cone, sphere, ellipsoid, elliptic hyperboloid, etc. (also elaborated in the course - Mathematics 2, in the same year of the studies) is necessary. Throughout two given 3D modeling tasks, students elaborate two separate subtopics: discretization of the surface elliptic hyperboloid of one sheet (ELHY) and spiral surfaces, both connected by key elements circular sections of quadrics. The subtopic's presentation methodology designed for students is conducted by "steps" in 3D structures modeling process, aided by applications and tools of most common engineering software Auto CAD. The applications presented below are created on a base of analytical geometry methods. The first topic - discretization of ELHY surface, i.e. generation of polygonal mesh structure, has a rather simple explanation and graphical presentation (wireframe and surface models) of geometrical procedures, i.e. constructions in opposite to the available analytical geometry solutions. A method of generating the ELHY surface is based on two arbitrary circular sections and one generatrix. The accompanying CAD application, created in Auto lisp, as a tool for discretization has the purpose to enable creative 3D task solution - model of geometric structure ELHY shaped. Three different options/solutions of discretization are offered. The second topic regarding 3D models of spiral surfaces/structures is nowadays very popular in the architecture. Here included spiral surfaces are one which geometric origins are quadrics. Since the term "spiral" is directly connected to the rotation and circle, geometric concept relay again on the circular sections of quadrics. This topic is supported by a Visual basic application (VBA) procedure implemented in Auto CAD. It also requires advanced 3D modeling tools for the design and visualization process of the final product. If comparing two given tasks, the second one is more creative and optional, while the students role in designing is more significant. However, we are sure that both tasks have an important educational value in better understanding of theory regarding quadric surfaces. It is reasonable to expect that in a certain moment (according to the level of programming knowledge) student could create his own software solution, or modify the offered one (application), aimed for such geometric topics. According to the palette of the surfaces included, variety of final "products" - structures and their purposes should be resulted in buildings, furniture, or art design

Dosimetry audit in radiotherapy centers in Serbia in 2016

U svrhu ispravne procene apsorbovanih doza za pacijente pri radioterapiji primenom polja gama zračenja (Co-60) kao i visokoenergetskih polja X-zračenja generisanih u linearnim akceleratorima, veći broj radioterapijskih centara iz Srbije je učestvovao u programu IAEA/WHO Postal Dose Quality Audit. Radiofotoluminescentni dozimetri (RPLD) su u okviru ovog programa postavljani u 15 polja X-zračenja različitih energija i jedno polje gama zračenja (Co-60) u različitim ustanovama, radi komparativne procene apsorbovane doze u vodi. Program je sproveden u periodu februar-maj 2016. godine.In order to accurately assess the absorbed dose delivered to the patients during the radiotherapy procedures, where Co-60 gamma radiation fields and high-energy X-ray radiation fields are employed, many of the radiotherapy centers in Serbia participated in the IAEA/WHO Postal Dose Quality Audit Program. Radio photoluminescent dosimeters were irradiated in 15 different X-ray ionizing radiation fields of various energies, and one gamma-ray radiation field (Co-60) in different radiotherapy centers. The study was performed in the period from February to May 2016.Зборник радова : XXIX симпозијум ДЗЗСЦГ : Сребрно језеро, 27-29. септембар 2017. годин

Build-Up PMMA Plate Effect on Calibration of TLD Reader

The routine monitoring of the occupationally exposed individuals constitutes an integral part of radiation protection program implemented at the Vinca Institute of Nuclear Sciences (INNV). The Individual monitoring service (IMS) at the INNV, accredited according to quality standard EN ISO/IEC 17025, is using Harshaw 6600 Plus automatic reader and thermoluminescent dosimeters (TLD) from two manufacturers (Harshaw, RadPro international GmbH). Working procedures are implemented according to Technical Recommendations for Monitoring Individuals Occupationally Exposed to External Radiation, RP 160 (European Commission, 2009). Among general consideration, RP 160 is suggesting that routine calibration of dosimetry system should be performed taking into consideration secondary charged particle equilibrium. As TLD system in use at IMS INNV comprises of TLD reader and of TLD cards, this consideration should be applied in both cases: when the reader and the TLD cards are being calibrated. During reader calibration, secondary charged particle equilibrium can be ensured using build-up PMMA plate of certain thickness placed in front of dosimeters. In this paper, influence of the build-up plate on reader calibration is being analyzed. This influence is observed through changes in reader calibration factor (RCF). RCF values obtained during reader calibration procedure with and without 2 mm thick build-up plate are presented. Exposures of whole body TLDs placed on slab phantom were done with Cs-137 radiation source located at Secondary Standard Dosimetry Laboratory (SSDL) at INNV. TLDs from both manufacturers had 2 detectors for measuring the dose equivalent at the depths of 10 mm and 0.07 mm. TLD reader was calibrated to measure effective dose in terms of Hp(10) and local skin dose in terms of Hp(0.07). RCF values for detectors measuring Hp(10), from both manufacturers, when irradiated without the plate were around 5% higher than RCF values obtained when irradiations were done with the plate. Values of RCFs for detectors measuring Hp(0.07) were around 1% higher when the plate had not been used. As RCF value is inversely proportional to measured dose, reader calibration without build-up plate, in terms of Hp(10), would lead to underestimated dose values. The observed RCF deviation of Hp(0.07) detector is regarded as consequence of exposure conditions uncertainties. In conclusion, if a constant geometry and constant operational conditions of TLDs are achieved, the only part of the TLD system that is not stable for a long time period is the TLD reader. To avoid inaccurate results, RCF should be orderly checked and reader calibration should be done according to widely accepted standards, currently in effect.3rd International Conference on Radiation and Applications in Various Fields of Research (RAD), Jun 08-12, 2015, Budva, Montenegr

Build-Up PMMA Plate Effect on Calibration of TLD Reader

The routine monitoring of the occupationally exposed individuals constitutes an integral part of radiation protection program implemented at the Vinca Institute of Nuclear Sciences (INNV). The Individual monitoring service (IMS) at the INNV, accredited according to quality standard EN ISO/IEC 17025, is using Harshaw 6600 Plus automatic reader and thermoluminescent dosimeters (TLD) from two manufacturers (Harshaw, RadPro international GmbH). Working procedures are implemented according to Technical Recommendations for Monitoring Individuals Occupationally Exposed to External Radiation, RP 160 (European Commission, 2009). Among general consideration, RP 160 is suggesting that routine calibration of dosimetry system should be performed taking into consideration secondary charged particle equilibrium. As TLD system in use at IMS INNV comprises of TLD reader and of TLD cards, this consideration should be applied in both cases: when the reader and the TLD cards are being calibrated. During reader calibration, secondary charged particle equilibrium can be ensured using build-up PMMA plate of certain thickness placed in front of dosimeters. In this paper, influence of the build-up plate on reader calibration is being analyzed. This influence is observed through changes in reader calibration factor (RCF). RCF values obtained during reader calibration procedure with and without 2 mm thick build-up plate are presented. Exposures of whole body TLDs placed on slab phantom were done with Cs-137 radiation source located at Secondary Standard Dosimetry Laboratory (SSDL) at INNV. TLDs from both manufacturers had 2 detectors for measuring the dose equivalent at the depths of 10 mm and 0.07 mm. TLD reader was calibrated to measure effective dose in terms of Hp(10) and local skin dose in terms of Hp(0.07). RCF values for detectors measuring Hp(10), from both manufacturers, when irradiated without the plate were around 5% higher than RCF values obtained when irradiations were done with the plate. Values of RCFs for detectors measuring Hp(0.07) were around 1% higher when the plate had not been used. As RCF value is inversely proportional to measured dose, reader calibration without build-up plate, in terms of Hp(10), would lead to underestimated dose values. The observed RCF deviation of Hp(0.07) detector is regarded as consequence of exposure conditions uncertainties. In conclusion, if a constant geometry and constant operational conditions of TLDs are achieved, the only part of the TLD system that is not stable for a long time period is the TLD reader. To avoid inaccurate results, RCF should be orderly checked and reader calibration should be done according to widely accepted standards, currently in effect.3rd International Conference on Radiation and Applications in Various Fields of Research (RAD), Jun 08-12, 2015, Budva, Montenegr

Experiments with RADFET dosimeter in electron-beams irradiation and numerical computation of the physical shielding factor

MOSFET electronic components are already the subject of several decades of research in various fields of dosimetry and radiation protection. Special interest appeared when these components are started to be used as dosimeters in radiotherapy with electron beams. However, if one looks much more serious in the wider scientific research horizon, all the results obtained in experiments with precisely defined energies of incident electrons can be used in other disciplines which consider the impacts spectra of cosmic radiation on electronic devices, which is especially importance for cosmic science and space research instrumentation. In this paper, one of the objectives was to examine the electrical characteristics specially designed ESAPMOS RADFET dosimeters in the experiments that were conducted on a linear accelerator installations. RADFET components are bombarded electron beams energy of 6 MeV and 8 MeV, and then are followed by changes in threshold voltage shift mean values depending on the change of absorbed dose is referred to as D(cGy) was determined in water. Conclusions performance RADFET components are more than encouraging in terms of further research to improve the linearity of the energy dependence as widely energy electrons. In the second part of the test complex structure of packaging components RADFET focus is placed on the determination of the energy deposited in layers that are of interest for the analysis of microscopic processes related to the recombination of radiation-induced electron-hole pairs. Transport incident electrons through all the layers of structure RADFET component type ESAPMOS was carried out numerical simulations of the Monte Carlo method using the software package FOTELP-2K12. On this occasion, were taken into account all the physical processes of interaction of electrons with materials given structure. When he conquered the numerical application of mathematical and physical model for determining the value of the absorbed energy as the energy deposited per unit mass in a given layers with different materials, it could be accessed defining physical shielding factor (PSF) for a given structure RADFET components. Physical shielding factor (PSF) is defined as the ratio of absorbed dose values, which in fact means that it is equal to the energy deposited when the RADFET is shielded with protection, and the RADFET without lid. When we know the energy dependence factor for PSF of RADFET with and without armour, can be carried out and the analysis of whether and to what extent the energy required compensating the electronic components. Monte Carlo simulations were performed for the transport of incident electrons from 4 MeV, 6 MeV, 8 MeV and 12 MeV. It can be concluded that the different energy of incident electrons there is a significant influence of material Kovar on the absorbed energy in SiO2 and Si layers structure RADFET, in cases where Kovar used among other things as physical protection.Third International Conference on Radiation and Applications in Various Fields of Research, RAD 2015, June 8-12, 2015, Budva, Montenegr

Uncertainty of calibration in the field of radiation protection

Cilj ovog rada je identifikacija relevantnih veličina koje doprinose ukupnoj mernoj nesigurnosti kalibracionog koeficijenta, a koje korišćenje etalonskog polja unosi u proces etaloniranja dozimetara u oblasti zaštite od zračenja. Na primeru je pokazano računanje kombinovane merne nesigurnosti za slučaj etalonskog polja generisanog radioaktivnim izvorom 60Co. Ovako izračunata merna nesigurnost iznosi 4.6% (k=2). Merna nesigurnost ovog reda veličine je adekvatna za etaloniranje velikog broja uređaja koji se koriste u zaštiti od zračenja, a čija je tačnost značajno manja od navedene vrednosti.The purpose of this paper is the identification of the relevant influence quantities contributing to the combined measurement uncertainty of calibration coefficient, that are introduced by using reference radiation qualities in the field of radiation protection. An example calculation of combined measurement uncertainty is shown for a 60Co radiation source. The calculated measurement uncertainty is 4.6% (k=2), and it is adequate for the purposes of calibration of many dosimeters used in the field of radiation protection, which have bad accuracy compared to the calculated value.XXVII Simpozijum Društva za zaštitu od zračenja Srbije i Crne Gore, Tara, 12-14. oktobar 2011

Contamination of the Šar Mountains Aquatorium – Kosovo with Depleted Uranium

The main objective of this study was to estimate the environmental and health risk of the Šar Mountains (Kosovo) for depleted uranium contamination. The risk assessment of the contamination is needed since, in the spring of 1999, conflict with bombarding took place in the territory of the Western Balkans, during which depleted uranium ammunition was used. In Serbia and Montenegro, such tests were performed; based on them, some territories were decontaminated. Šar Mountains is particularly important as it is one of the few water-rich areas in Kosovo. Therefore, soil and water samples were taken from characteristic places in the Šar Mountains aquatorium. Tests of the samples were performed under well-controlled conditions. The measurement uncertainty was less than 5%. Based on the obtained results, it was concluded that there was no contamination of the Šar Mountains with depleted uranium. This conclusion can be extended to the broader area around the Šar Mountains, as it is a safe area surrounded by high mountains