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

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

Assessment of Occupational Dose in Fluoroscopy Procedures When Individual Monitoring Is Not Utilized

Fluoroscopy procedures may lead to increased radiation exposure of radiologists and other staff members. The objective of the study is to assess whole body radiation doses and doses to the eye in fluoroscopy procedures, based on measurements that allow for estimates of occupational doses when personal dosimeters have not been used. Four geometrical configurations were considered: overcouch x-ray tube with and without table mounted lead rubber curtains in place, undercouch x-ray tube with horizontal x-ray beam and undercouch x-ray tube with vertical x-ray beam. The doses were estimated using distribution of the scattered radiation and typical workload, as well as the pattern of used of protective tools. Estimated effective dose was in the range from few to 60 mu Sv per procedure for radiologist, and from few to 20 mu Sv per procedure for radiographer, depending on the geometrical configuration and level of personal protection. Corresponding unprotected eye doses were estimated to be in the range 0.03 - 2.8 mSv per procedure for radiologist and 0.02-0.78 mSv for radiographer. The presented results allowed for realistic estimations of the occupational whole body dose and dose to the eyes from the workload of the staff members and from the level of use of radiation protection tools when personal dosimeters have not been regularly used.3rd International Conference on Radiation and Applications in Various Fields of Research (RAD), Jun 08-12, 2015, Budva, Montenegr

Degradation Effects of the Output Electrical Characteristics of Si Solar Cells as a Result of Ionizing Radiation under Low Light Conditions

This paper presents results of radiation resistance of different types of commercially available single- and poly-crystalline silicon solar cells. Sample cells were subjected to gamma radiation from gamma radiation source Co-60. Characteristic parameters of solar cells were extracted from obtained I-V curves: open circuit voltage, short circuit current, maximum power point voltage and current, efficiency, fill factor, and series resistance. Obtained results show the level of parameters degradation with purpose of increasing solar cells applications in radiation environments

An Assessment of Scattered Radiation During Fluoroscopic Procedures in Diagnostic Radiology

The results of measurements of scattered radiation in the vicinity of a fluoroscopic X-ray facility are presented in this paper. Two different fluoroscopic systems, one with an undercouch tube and one with an overcouch tube, were compared. The dose rate was measured during the simulation of a fluoroscopy procedure, using an ionization chamber as a dosemeter. The distribution of scattered radiation has been determined and results show a much higher dose rate in cases of an overcouch tube arrangement. When X-ray units with an undercouch tube are concerned, under same exposure conditions, the dose rate is higher in cases of a vertical beam. Prior to the measurements, the ionization chamber was examined in order to evaluate its suitability as a survey meter used in diagnostic radiology. Measurements show that below 1.2 s, the ionization chamber gives an underestimation of dose rates. Therefore, in order to perform accurate measurements using this instrument, exposure times should be above 1.2 s

The impact of field size and radiation quality on KAP-meter and CT-chamber response

Kerma-area product and kerma-length product are important practical dosimetric quantities used in diagnostic radiology. These quantities are measured by special types of dosimeters which are calibrated in standard radiation qualities established in calibration laboratories. However, in clinical practice the dosimeters are used in different conditions, including the radiation quality and field size. In this paper, energy and field size dependence are studied for both types of dosimeters. One dosimeter of each type is tested. The KAP-meter has shown significant dependence on both radiation quality and field size, while the dependence of the CT-chamber is much less pronounced. Two different approaches can be used to correct for the difference between conditions during calibration and in clinical practice. When the clinical beam is well characterized and energy and field size dependence of the dosimeter are well known, the optimum solution is to apply the adequate correction factor to the measurements, keeping measurement uncertainty as low as possible. If this is not the case, the above limitations must be taken under consideration in the calculation of the expanded uncertainty budget

The effects induced by the gamma-ray responsible for the threshold voltage shift of commercial p-channel power VDMOSFET

The variations in the threshold voltage shift in p-channel power VDMOSFET during the gamma ray irradiation was investigated in the dose range from 10 to 100 Gy. The investigations were performed without the gate bias and with 5 V gate bias. The devices with 5 V gate bias exhibit a linear dependence between the threshold voltage shift and the radiation dose. The densities of radiation-induced fixed and switching traps were determined from the sub-threshold I-V characteristics using the midgap technique. It was shown that the creation of fixed traps is dominant during the irradiation. The possible mechanisms responsible for the fixed and switching traps creation are also analyzed in this paper

Monte Carlo simulation of radiation damage in shielding materials of Am-Be-241 neutron source

Radijaciona oštećenja nastaju usled izmeštanja atoma materijala pri elastičnom rasejavanju čestica upadnog zračenja na jezgrima ili zbog nuklearnih reakcija izazvanih upadnim zračenjem. Broj izmeštanja po atomu (DPA) je veličina kojom se opisuje radijaciono oštećenje. S obzirom da je neutronsko zračenje naročito efikasno u izmeštanju atoma, ispitan je uticaj neutrona na sastavne elemente strukturalne zaštite 241Am-Be neutronskog izvora sastavljene od parafina, betona i olova. Proračun DPA je obavljen na osnovu rezultata simulacija primenom MCNPX prorgamskog paketa.Radiation damage in materials results from nuclear collisions and reactions which produce energetic recoil atoms of the host materials or reaction products. Displacement per atom (DPA) is used to quantify radiation damage. Since neutrons are particularly efficient in displacing atoms, their influence on constituent elements of 241Am-Be neutron source shielding made of paraffin, concrete and lead. DPA was calculated based on simulations using MCNPX