Browsing by Author "Yegin, G"

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    Differential dose contributions on total dose distribution of 125I brachytherapy source
    Camgöz, B; Yegin, G; Kumru, MN
    This work provides an improvement of the approach using Monte Carlo simulation for the Amersham Model 6711 I-125 brachytherapy seed source, which is well known by many theoretical and experimental studies. The source which has simple geometry was researched with respect to criteria of AAPM Tg-43 Report. The approach offered by this study involves determination of differential dose contributions that come from virtual partitions of amassive radioactive element of the studied source to a total dose at analytical calculation point. Some brachytherapy seeds contain multi-radioactive elements so the dose at any point is a total of separate doses from each element. It is momentous to know well the angular and radial dose distributions around the source that is located in cancerous tissue for clinical treatments. Interior geometry of a source is effective on dose characteristics of a distribution. Dose information of inner geometrical structure of a brachytherapy source cannot be acquired by experimental methods because of limits of physical material and geometry in the healthy tissue, so Monte Carlo simulation is a required approach of the study. EGSnrc Monte Carlo simulation software was used. In the design of a simulation, the radioactive source was divided into 10 rings, partitioned but not separate from each other. All differential sources were simulated for dose calculation, and the shape of dose distribution was determined comparatively distribution of a single-complete source. In this work anisotropy function was examined also mathematically. (C) 2010 Greater Poland Cancer Centre, Poland. Published by Elsevier Urban & Partner Sp. z.o.o. All rights reserved.
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    Estimation of bremsstrahlung photon fluence from aluminum by artificial neural network
    Akkurt, I; Gunoglu, K; Tekin, HO; Demirci, ZN; Yegin, G; Demir, N
    Background: As bremsstrahlung photon beam fluence is important parameter to be known in a photonuclear reaction experiment as the number of produced particle is strongly depends on photon fluence. Materials and Methods: Photon production yield from different thickness of aluminum target has been estimated using artificial neural network (ANN) model. Target thickness and incoming electron energy has been used as input in ANN model and the photon fluence was output. Results: The results were estimated using ANN model for three different thickness and compared with the results obtained by EGS (Electron Gamma Shower) simulation. Conclusion: It can be concluded from this work that the bremsstrahlung photon fluence can be obtained using ANN model. Iran. J. Radiat. Res., 2012; 10(1): 63-65
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    Improving the resolution of beta scattering spectroscopy
    Celiktas, C; Selvi, S; Yegin, G
    We have examined the performance of a modified beta-ray spectrometer using a pulse shape analyzer/timing single channel analyzer and related electronics, thereby preserving the low energy electron tail in measurement of the scattered electron spectra from an n-type Si wafer target. Comparison of measurements with the scattering spectra calculated by the Monte Carlo program EGS4 indicates good agreement across a significant part of the spectrum, an exception being for the energy region 30-100 keV. Re-evaluation of existing scattering cross-sections would be useful, as would possible geometrical effects of the scattering arrangement used herein. Present efforts seek to contribute to the evaluation of electron scattering cross-sections and improvement in theoretical models. (C) 2004 Elsevier Ltd. All rights reserved.
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    A new approach to geometry modeling for Monte Carlo particle transport: An application to the EGS code system
    Yegin, G
    A new technique has been developed for Monte Carlo particle transport calculations to handle the geometry for systems having complex structure. In this technique, the geometry of a problem is determined as a superposition of many simple geometries in the same space. The actual geometry of a region is determined by picking between these geometries based upon which one is real and which are virtual at a particular point in space. This method was applied in the EGS code system. The effect of this method on computation time and accuracy of the results are discussed. (C) 2003 Elsevier B.V. All rights reserved.
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    Comment on 'egs_brachy: a versatile and fast Monte Carlo code for brachytherapy'
    Yegin, G
    In a recent paper (Chamberland et al 2016 Phys. Med. Biol. 61 8214) develop a new Monte Carlo code called egs_brachy for brachytherapy treatments. It is based on EGSnrc, and written in the C++ programming language. In order to benchmark the egs_brachy code, the authors use it in various test case scenarios in which complex geometry conditions exist. Another EGSnrc based brachytherapy dose calculation engine, BrachyDose, is used for dose comparisons. The authors fail to prove that egs_brachy can produce reasonable dose values for brachytherapy sources in a given medium. The dose comparisons in the paper are erroneous and misleading. egs_brachy should not be used in any further research studies unless and until all the potential bugs are fixed in the code.
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    Evaluation of BrachyDose Monte Carlo code for HDR brachytherapy: dose comparison against Acuros®BV and TG-43 algorithms
    Dagli, A; Yurt, F; Yegin, G
    Aim: The aim of this study is to investigate the accuracy of dose distributions calculated by the BrachyDose Monte Carlo (MC) code in heterogeneous media for high-dose-rate (HDR) brachytherapy and to evaluate its usability in the clinical brachytherapy treatment planning systems. Materials and methods: For dose comparisons, three different dose calculation algorithms were used in this study. Namely, BrachyDose MC code, Eclipse TG-43 dose calculation tool and Acuros (R) BV model-based dose calculation algorithm (MBDCA). Dose distributions were obtained using any of the above codes in various scenarios including 'homogenous water medium scenario', an 'extreme case heterogeneous media scenario' and clinically important 'a patient with a cervical cancer scenario'. In the 'extreme case, heterogeneous media scenario', geometry is a rare combination of unusual high-density and low-density materials and it is chosen to provide a test environment for the propagation of photons in the interface of two materials with different absorption and scattering properties. GammaMed Ir-192 Model 12i Source is used as the HDR brachytherapy source in this study. Dose calculations were performed for the cases where there is either a single source or five sources planted into the phantom geometry in all homogenous water phantom and extreme case heterogeneous media scenarios. For the scenario a patient with a cervical cancer, dose calculations were performed in a voxelized rectilinear phantom, which is constructed from a series of computed tomography (CT) slices of a patient, which are obtained from a CT device. Results: In homogeneous water phantom scenario, we observed no statistically significant dose differences among the dose distributions calculated by any of the three algorithms at almost every point in the geometry. In the extreme case heterogeneous media scenario, the dose calculation engines Acuros (R) BV and BrachyDose are agreed well within statistics in every region of the geometry and even in the points close to the interfaces of low-density and high-density materials. On the other hand, the dose values calculated by these two codes are significantly different from those calculated by the TG-43 algorithm. In the 'a patient with a cervical cancer scenario', the calculated D-2cc dose difference between Acuros (R) BV and BrachyDose codes is within 2% in the rectum and 11% for the bladder and sigmoid. There was no meaningful difference in the mean dose values between MBDCAs in the bone structures. Conclusions: In this study, the accurate dose calculation capabilities of the BrachyDose program in HDR brachytherapy were investigated on various scenarios and, as a MC dose calculation tool, its effectiveness in HDR brachytherapy was demonstrated by comparative dose analysis.