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Variance reduction techniques (VRTs) have been tremendously successful when applied to Monte Carlo radiation transport codes for which the computation time constitutes an important and a problematic parameter. In fact, many Monte Carlo calculations absolutely require variance reduction methods to achieve practical computation times. The MCNPX code...
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Free Electron Laser, FLASH (Free Electron Laser in Hamburg) at DESY is driven by a 1.25 GeV superconducting electron linac. During its operation FLASH produces parasitic (pulsed) radiations made of gamma rays (bremsstrahlung) and photoneutrons, caused by the interaction of field emission-and dark-current induced electrons with the accelerator compo...
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... When VRT was implemented, 30 days were saved, allowing Geometry 2 to complete the simulation in 16 days, suggesting that narrowing source height accelerated the simulation of Geometry 2 by about 65%. The results were as expected while both sources of volume and photons decreased simultaneously, given the computation time in MCNP was proportional to the total number of particles generated (Zoubair et al., 2013). Due to this, the overall amount of time needed to run all of the photons was drastically reduced, which was regarded as a successful outcome. ...
Monte Carlo N-Particle (MCNP) simulation has been extensively proven in nuclear medicine imaging systems, most notably in designing and optimizing new medical imaging tools. It enables more complicated geometries and the simulation of particles passing through and interacting with materials. However, a relatively long simulation time is a drawback of Monte Carlo simulation, mainly when complex geometry exists. The current study presents an alternative variance reduction technique for a modeled positron emission tomography (PET) camera by reducing the height of the source volume definition while maintaining the geometry of the simulated model. The National Electrical Manufacturers Association (NEMA) of the International Electrotechnical Commission (IEC) PET's phantom was used with a 1 cm diameter and 7 cm height of line source placed in the middle. The first geometry was fully filled the line source with 0.50 mCi radioactivity. In contrast, the second geometry decreased the source definition to 2.4 cm in height, covering 1 cm above and below the sub-block detector level. The source volume definition approach led to a 71% reduction in the total photons to be simulated. Results showed that the proposed variance reduction strategy could produce spatial resolution as precise as fully filled geometry and sped up the simulation time by approximately 65%. Hence, this strategy can be utilized for further PET optimizing simulation studies.
... In this research we used MCNP 6.2 general use radiation transport code to design a 12 MV LINAC (Zoubair, et al, 2013) (Zeghari, Saaidi ve El Moursli,2020), with detailed parts including target to produce bremsstrahlung, flattening filter (FF), ion chamber, primary collimator, and secondary collimators with adjustable X and Y jaws. Flattening filter materials of Al, Stainless Steel, Sn, Ta and Hg were used as well as a flattening filter free (FFF) system. ...
ABSTRACT
Objective: To analyze the performance of the first trimester Down syndrome screening in a single medical
center in Bitola Macedonia.
Materials and methods: From January 2016 to January 2022, a total of 2977 pregnant women at gestational
age of 10 weeks to 13 weeks 6 days received first trimester “combined test” for Down syndrome screening.
The test combines the ultrasound scan of nuchal translucency thickness and maternal biochemical serum
levels of pregnancy-associated plasma protein A (PAPP-A) and free beta-human chorionic gonadotropin
(bhCG). A positive screen was defined as an estimated Down syndrome risk 1/270, and either chorionic
villous sampling or amniocentesis was performed for fetal chromosomal analyses.
Results: 7% of pregnancies were proven to have fetal chromosome anomalies. The detection rates for trisomy
21and trisomy 18 were 82% (176), 18% (39).
Conclusion: The first trimester combined test is an effective screening tool for Down syndrome detection
with an acceptable low false positive rate. The best timing of screening will be between 11 and 12 weeks’
gestation.
... In the last years, there have been rapid developments in computer technology that lead to exponential increase in processor speed, as well as improvements in software optimization and networking technology and have made MC technique treatment planning a feasible choice (Caccia et al., 2007;Foley, Conneely, Alexander, Stroian, & Seuntjens, 2013). A number of MC codes are now in clinical use, such as BEAMnrc, VMC++ (Hasenbalg, Fix, Born, Mini, & Kawrakow, 2008), PENELOPE (Brualla, Rodriguez, Sempau, & Andreo, 2019;Sempau, Badal, & Brualla, 2011), GEANT4 (EL Bakkali et al., 2016), MCNPX (Zoubair et al., 2013). ...
... Mohammed, Chakir, Boukhal, Saeed, and El Bardouni (2016) found a rising of efficiency by 1130 time compared with analog simulation. Zoubair et al. (2013) found a rising of efficiency for accelerated simulation by 737.22 times compared with analog simulation. Fragoso, Kawrakow, Faddegon, Timothy, and Chetty (2009) found the highest relative efficiencies were 935 times compared to simulation without VRTs on a single 2.6 GHz processor. ...
Monte Carlo (MC) calculations used to require long CPU times, which made it prohibitive for routine clinical use. Several variance reduction techniques (VRTs) are included in the BEAMnrc MC code to significantly improve the efficiency of photon beams for which the computation time constitutes a problematic parameter. This work focused on the optimization of VRTs parameters to improve the efficiency by BEAMnrc code. This work deals with the use of different VRTs parameters alone or combined, such as directional bremsstrahlung splitting (DBS), uniform bremsstrahlung splitting (UBS), photon and electron splitting, Russian roulette (RR), range rejection, and bremsstrahlung cross section enhancement (BCSE) included in BEAMnrc code. We found that the relative improvement in efficiency due to UBS without RR, ICM_SPLIT (e-/e+), BCSE, and DBS is over 85, 130, 3489, and 4652 times higher in comparison to analog simulation for total photon fluence efficiency in 12 MV photon beam, respectively. VRTs combined in parallel simulation lead to enhance the dose efficiency by 19321 times compared to analog simulation. It is demonstrated that it is possible to further improve the efficiency by optimizing VRTs parameters combined and at the same time preserving its accuracy in parallel simulation of a 12 MV photon beam.
It is demonstrated that it is possible to further improve the efficiency by optimizing VRTs parameters combined and at the same time preserving its accuracy in parallel simulation of a 12 MV photon beam.
... The calculated photon spectrum has a mean energy of 3.30 MeV inside the identified square field. The results obtained are compared to those found in previous studies realized by different MC codes, and summarized in Table 2. Table 2 shows that our results are close to those obtained by other codes especially with MCNP and Geant4 (Blazy et al., 2006;Zoubair et al., 2013;El Bakali, 2014). So, we can say that GAMOS model of SATURNE43 medical accelerator is accurately simulated and the initial parameters of electron beam were determined precisely. ...
... Mean energy GAMOS (This work) 3.30 MCNP Zoubair et al. (2013) 3.39 Geant4 El Bakali (2014) 3.34 Penelope Blazy et al. (2006) 3.24 Fig. 6. Monte Carlo calculated photon spectrum at SSD of 90 cm for 11.8 MV photon beam. ...
The Monte Carlo method is considered the most accurate method for dose calculation in radiotherapy.
The Linear accelerator (Linac) is currently the most widely used in radiotherapy center machines. This
study aims at validating the GAMOS code based on the Geant4 Monte Carlo toolkit. A Saturne43 LINAC
of 12 MV photon beam was modeled for configuring a 10 *10 cm2 radiation field. The electron beam
parameters such as spot size and mean energy were tuned by comparing calculated dose distribution
within homogenous water phantom with a measured one. The results obtained showed that the depth
dose and lateral dose profiles are sensitive to the electron beam parameters studied. The best matching
with measured was found when the appropriate mean electron energy and beam width were 11.8 MeV
and 2 mm respectively.
... Comparison between BEAMnrc and MCNPX (Zoubair et al. 2013) carried out previous study in our laboratory ERSN for simulation a Saturne43 accelerator of 12 MV for 10 Â 10 cm 2 field size using MCNPX (Monte Carlo N-Particle) Monte Carlo simulation which is developed by Los Alamos National Laboratory (LANL) and can be used to simulate many types of particles electron, photon, neutron and proton (Anonyms 2 n.d.). She validated MCNPX code by compared her results with the experimental data obtained at the French National Metrological Laboratory for ionizing radiation (LNHB). ...
The application of Variance Reduction Techniques (VRT) in Monte Carlo (MC) codes brings significant improvement in efficiency and a significant profit in the time of simulation. Monte Carlo radiation transport codes have provided by these techniques to solve the time problematic. BEAMnrc Monte Carlo code has several techniques, that have enabled to be the best and fastest code, Including rang rejection, photon forcing, splitting of photon or electron, (Direction, Selective and Uniform) Bremsstrahlung Photon Splitting and Russian roulette (RR). This paper aims to analysis the variance reduction techniques available in BEAMnrc code, validation BEAMnrc model for simulation a Saturne43 accelerator of 12 MV photon beam, and comparing between MCNPX and BEAMnrc.
The results obtained show that employing of Direction Bremsstrahlung Photon Splitting (DBS) technique alone or combined with others techniques lead to enhance the efficiency in BEAMnrc simulation. It improves by 16 times compared with Selective Bremsstrahlung Photon Splitting (SBS), 3.7 times (without RR) and it increases about 29 times (with RR) compared to Uniform Bremsstrahlung Photon Splitting (UBS), and also the efficiency increases by factor of 1130 compared to analogue simulation.
A good agreement between measurement and calculation of PDD curves for 10×10 cm2 of 12 MV photon beam with local differences less than 2% has been obtained.
BEAMnrc has an efficiency greater than MCNPX code in case of analogue simulation (without VRTs).
The use of Monte Carlo methods for the set up of Treatment Planning Systems (TPS) in radiotherapy applications is a current standard. The most advanced modeling techniques aim at directly link the output of CT scans to a patient-specific model build up instead of standard phantoms and look-up tables. This link represents a critical step since even the most accurate segmentation and organ volume definition must be translated into a suitable input for the Monte Carlo code. During that step, the segmented volume is usually mapped on a regular geometrical lattice (voxels). A more sophisticated option appears to be a volume description based on an Unstructured Mesh (UM) geometry typical of current finite element codes. In this paper, we compared the two approaches analyzing the bias induced by the different choices. Starting from anonymous patient DICOM files coming from a CT scan, suitable segmentation and volume definition have been carried out and voxel and UM-based equivalent models for the Monte Carlo code MCNP6 have been built. Some computational phantoms, covering some significant portion of the human body (head and lower limb), have been used as a benchmark of the dose distribution obtained from X-ray sources commonly used in orthovoltage applications. The specific clinical application has been chosen because, despite being used on a growing number of patients and with multi-Gy doses, treatment planning is still based on poorly characterized dose mapping systems such as look-up tables or low-resolution computational phantoms for MC codes. Also, experimental measurements on phantom slabs irradiated by an X-ray source were carried out preliminarily to validate the simulated radiation source. As shown in the results, the UM computational phantoms (built through the Simpleware SCAN-IP™ tool) can reduce the bias induced by the regularity of the classical cubic voxel geometry, give a more accurate description of volumes and complex surfaces and, thanks to an optimized discretization of the volumes, are also able to reduce the computational work. For the same UM models, various comparisons with different voxel sizes have been produced to investigate the dose distributions and evaluate the voxelization effects. The comparison shows a convergence pattern of the voxel model to the UM one. It has been possible to verify that the most significant bias occurs where the dose gradient is higher, along the beam borders and at tissue interfaces. The simulations showed that the UM can be really effective and reliable to compute the dose distributions within computational anthropomorphic phantoms obtained from the patient’s CT scans.
A multi-scale Monte Carlo model is proposed to assess the dosimetric and biological impact of iodine-based contrast agents commonly used in computed tomography. As presented, the model integrates the general purpose MCNP6 code system for larger-scale radiation transport and dose assessment with the Monte Carlo damage simulation to determine the sub-cellular characteristics and spatial distribution of initial DNA damage. The repair-misrepair-fixation model is then used to relate DNA double strand break (DSB) induction to reproductive cell death. Comparisons of measured and modeled changes in reproductive cell survival for ultrasoft characteristic k-shell x-rays (0.25–4.55 keV) up to orthovoltage (200–500 kVp) x-rays indicate that the relative biological effectiveness (RBE) for DSB induction is within a few percent of the RBE for cell survival. Because of the very short range of secondary electrons produced by low energy x-ray interactions with contrast agents, the concentration and subcellular distribution of iodine within and near cellular targets have a significant impact on the estimated absorbed dose and number of DSB produced in the cell nucleus. For some plausible models of the cell-level distribution of contrast agent, the model predicts an increase in RBE-weighted dose (RWD) for the endpoint of DSB induction of 1.22–1.40 for a 5–10 mg ml⁻¹ iodine concentration in blood compared to an RWD increase of 1.07 ± 0.19 from a recent clinical trial. The modeled RWD of 2.58 ± 0.03 is also in good agreement with the measured RWD of 2.3 ± 0.5 for an iodine concentration of 50 mg ml⁻¹ relative to no iodine. The good agreement between modeled and measured DSB and cell survival estimates provides some confidence that the presented model can be used to accurately assess biological dose for other concentrations of the same or different contrast agents.
