Monte Carlo Algorithm-Based Dosimetric Comparison between Commissioning Beam Data across Two Elekta Linear Accelerators with AgilityTM MLC System (original) (raw)
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2020
BEAMnrc/DOSXYZnrc Monte Carlo code is widely used for accurate dose calculation. This study simulated and tested two incident electron-source parameters on dosimetric characteristics of photon beam for an Elekta Precise linear accelerator (linac) model. The linac model of a 6 MV photon beam for 10 × 10 cm2 field was used to investigate the sensitivity of the two-incident electron sources. Optimal source parameter was achieved by varying the parallel and mean angular spread (2D Gaussian distribution) circular beam sources. In a parallel incident electron source, the beam radius (r) parameter was varied while the sigma (σ) parameter in the mean angular spread beam source was varied. The accuracy of this source model was evaluated by calculating the dose distribution in a homogeneous water phantom. The simulated data were benchmarked with measurements for percentage depth doses (PDDs) and lateral dose profiles using 2%/2mm and 3%/3mm gamma (γ) criteria. This study showed that variation...
Physica Medica, 2009
In the present work, Monte Carlo (MC) models of electron beams (energies 4, 12 and 18 MeV) from an Elekta SL25 medical linear accelerator were simulated using EGSnrc/BEAMnrc user code. The calculated dose distributions were benchmarked by comparison with measurements made in a water phantom for a wide range of open field sizes and insert combinations, at a single source-to-surface distance (SSD) of 100 cm. These BEAMnrc models were used to evaluate the accuracy of a commercial MC dose calculation engine for electron beam treatment planning (Oncentra MasterPlan Treament Planning System (OMTPS) version 1.4, Nucletron) for two energies, 4 and 12 MeV. Output factors were furthermore measured in the water phantom and compared to BEAMnrc and OMTPS. The overall agreement between predicted and measured output factors was comparable for both BEAMnrc and OMTPS, except for a few asymmetric and/or small insert cutouts, where larger deviations between measurements and the values predicted from BEAMnrc as well as OMTPS computations were recorded. However, in the heterogeneous phantom, differences between BEAMnrc and measurements ranged from 0.5 to 2.0% between two ribs and 0.6e1.0% below the ribs, whereas the range difference between OMTPS and measurements was the same (0.5e4.0%) in both areas. With respect to output factors, the overall agreement between BEAMnrc and measurements was usually within 1.0% whereas differences up to nearly 3.0% were observed for OMTPS. This paper focuses on a comparison for clinical cases, including the effects of electron beam attenuations in a heterogeneous phantom. It, therefore, complements previously reported data (only based on measurements) in one other paper on commissioning of the VMCþþ dose calculation engine.
2015
Simulation of a linear accelerator (linac) head requires determining the parameters that characterize the primary electron beam striking on the target which is a step that plays a vital role in the accuracy of Monte Carlo calculations. In this work, the commissioning of photon beams (6 MV and 15 MV) of an Elekta Precise accelerator, using the Monte Carlo code EGSnrc, was performed. The infl uence of the primary electron beam characteristics on the absorbed dose distribution for two photon qualities was studied. Using different combinations of mean energy and radial FWHM of the primary electron beam, deposited doses were calculated in a water phantom, for different fi eld sizes. Based on the deposited dose in the phantom, depth dose curves and lateral dose profi les were constructed and compared with experimental values measured in an arrangement similar to the simulation. Taking into account the main differences between calculations and measurements, an acceptability criteria based ...
Medical physics, 2018
Reference dosimetry data can provide an independent second check of acquired values when commissioning or validating a treatment planning system (TPS). The Imaging and Radiation Oncology Core at Houston (IROC-Houston) has measured numerous linear accelerators throughout its existence. The results of those measurements are given here, comparing accelerators and the agreement of measurement versus institutional TPS calculations. Data from IROC-Houston on-site reviews from 2000 through 2014 were analyzed for all Elekta accelerators, approximately 50. For each, consistent point dose measurements were conducted for several basic parameters in a water phantom, including percentage depth dose, output factors, small-field output factors, off-axis factors, and wedge factors. The results were compared by accelerator type independently for 6, 10, 15, and 18 MV. Distributions of the measurements for each parameter are given, providing the mean and standard deviation. Each accelerator's meas...
Distributions dose analysis for 6 MV photon beams using Monte Carlo-GEANT4 simulation
THE 8TH NATIONAL PHYSICS SEMINAR 2019
Monte Carlo is a method that widely used for calculation of particle transport in radiotherapy dose distribution. This study was devoted to develop a linear accelerator head geometry model (LINAC) using GEANT4 simulation for 6 MeV photon beam. The geometric model of the accelerator head consists of electron sources, target, primary collimator, flattening filter, jaws, and MLC (multi-leaf collimator). The homogeneous water phantom size of 40 x 40 x 40 cm 3 was used in the simulation, 100 cm SSD (source-skin distance), and field size are 5 cm x 5 cm, 10 cm x 10 cm, 20 cm x 20 cm, and 30 cm x 30 cm. The simulation results show the peak curve energy positions are in the range 0.3 MeV-0.4 MeV and the maximum absorbed energy is about 5.9 MeV. According to the landau curve fitting the mean energy is about 0.385 MeV. The results of GEANT4 simulation show the energy spectrum has the same pattern as an energy spectrum from several experiments of LINAC head geometry. The simulation results also show the dose distribution based on beam profile and depth profile of water phantom with different fields.
Monte Carlo modeling of electron beams from a NEPTUN 10PC medical linear accelerator
Nukleonika
The Monte Carlo (MC) simulation of radiation transport is considered to be one of the most accurate methods of radiation therapy dose calculation. With the rapid development of computer technology, MC-based treatment planning for radiation therapy is becoming practical. A basic requirement for MC treatment planning is a detailed knowledge of radiation beams of medical linear accelerators (linacs). A practical approach to acquire this knowledge is to perform MC simulation of radiation transport for linacs. The aims of this study were: modeling of the electron beams from the NEPTUN 10PC linear accelerator (linac) with the MC method, obtaining of the energy spectra of electron beams, and providing the phase-space files for the electron beams of this linac at different field sizes. Electron beams produced by the linac were modeled using the BEAMnrc MC system. Central axis depth-dose curves and dose profiles of the electron beams were measured experimentally and also calculated with the MC system for different field sizes and energies. In order to benchmark the simulated models, the percent depth dose (PDD) and dose-profile curves calculated with the MC system were compared with those measured experimentally with diode detectors in an RFA 300 water phantom. The results of this study showed that the PDD and dose-profile curves calculated by the MC system using the phase-space data files matched well with the measured values. This study demonstrates that the MC phase-space data files can be used to generate accurate MC dose distributions for electron beams from NEPTUN 10PC medical linac.
Medical Physics, 2004
The purpose of this study is to perform a clinical evaluation of the first commercial ͑MDS Nordion, now Nucletron͒ treatment planning system for electron beams incorporating Monte Carlo dose calculation module. This software implements Kawrakow's VMC ϩϩ voxel-based Monte Carlo calculation algorithm. The accuracy of the dose distribution calculations is evaluated by direct comparisons with extensive sets of measured data in homogeneous and heterogeneous phantoms at different source-to-surface distances ͑SSDs͒ and gantry angles. We also verify the accuracy of the Monte Carlo module for monitor unit calculations in comparison with independent hand calculations for homogeneous water phantom at two different SSDs. All electron beams in the range 6 -20 MeV are from a Siemens KD-2 linear accelerator. We used 10 000 or 50 000 histories/cm 2 in our Monte Carlo calculations, which led to about 2.5% and 1% relative standard error of the mean of the calculated dose. The dose calculation time depends on the number of histories, the number of voxels used to map the patient anatomy, the field size, and the beam energy. The typical run time of the Monte Carlo calculations (10 000 histories/cm 2 ) is 1.02 min on a 2.2 GHz Pentium 4 Xeon computer for a 9 MeV beam, 10ϫ10 cm 2 field size, incident on the phantom 15ϫ15ϫ10 cm 3 consisting of 31 CT slices and voxels size of 3ϫ3ϫ3 mm 3 ͑total of 486 720 voxels͒. We find good agreement ͑discrepancies smaller than 5%͒ for most of the tested dose distributions. We also find excellent agreement ͑discrepancies of 2.5% or less͒ for the monitor unit calculations relative to the independent manual calculations. The accuracy of monitor unit calculations does not depend on the SSD used, which allows the use of one virtual machine for each beam energy for all arbitrary SSDs. In some cases the test results are found to be sensitive to the voxel size applied such that bigger systematic errors (Ͼ5%) occur when large voxel sizes interfere with the extensions of heterogeneities or dose gradients because of differences between the experimental and calculated geometries. Therefore, user control over voxelization is important for high accuracy electron dose calculations.
Physics of Particles and Nuclei Letters
Abstract⎯The Monte Carlo model for the photon-beam output from the Varian Clinac 2100 linear accelerator was validated to compare the calculated to measured PDD and beam dose profiles The Monte Carlo calculation method is considered to be the most accurate method for dose calculation in radiotherapy. The objective of this study is to build a Monte Carlo geometry of Varian Clinac 2100 linear accelerator as realistically as possible. The Monte Carlo codes used in this work were the BEAMnrc code to simulate the photons beam and the DOSXYZnrc code to examinate the absorbed dose in the water phantom. We have calculated percentage depth dose (PDD) and beam profiles of the 6 MV photon beam for the 6 × 6 cm 2 , 10 × 10 cm 2 and 15 × 15 cm 2 field sizes. We have used the gamma index technique for the quantitative evaluation to compare the measured and calculated distributions. Good agreement was found between calculated PDD and beam profile compared to measured data. The comparison was evaluated using the gamma index method and the criterions were 3% for dose difference and 3 mm for distance to agreement. The gamma index acceptance rate was more than 97% of both distribution comparisons PDDs and dose profiles and our results were more developed and accurate. The Varian Clinac 2100 linear accelerator was accurately modeled using Monte Carlo codes: BEAMnrc and DOSXYZnrc codes package.
Comparison of measured and Monte Carlo calculated dose distributions from the NRC linac
Medical Physics, 2000
We have benchmarked photon beam simulations with the EGS4 user code BEAM ͓Rogers et al., Med. Phys. 22, 503-524 ͑1995͔͒ by comparing calculated and measured relative ionization distributions in water from the 10 and 20 MV photon beams of the NRC linac. Unlike previous calculations, the incident electron energy is known independently to 1%, the entire extra-focal radiation is simulated, and electron contamination is accounted for. The full Monte Carlo simulation of the linac includes the electron exit window, target, flattening filter, monitor chambers, collimators, as well as the PMMA walls of the water phantom. Dose distributions are calculated using a modified version of the EGS4 user code DOSXYZ which additionally allows scoring of average energy and energy fluence in the phantom. Dose is converted to ionization by accounting for the (L /) air water variation in the phantom, calculated in an identical geometry for the realistic beams using a new EGS4 user code, SPRXYZ. The variation of (L /) air water with depth is a 1.25% correction at 10 MV and a 2% correction at 20 MV. At both energies, the calculated and the measured values of ionization on the central axis in the buildup region agree within 1% of maximum ionization relative to the ionization at 10 cm depth. The agreement is well within statistics elsewhere. The electron contamination contributes 0.35(Ϯ0.02) to 1.37(Ϯ0.03)% of the maximum dose in the buildup region at 10 MV and 0.26(Ϯ0.03) to 3.14(Ϯ0.07)% of the maximum dose at 20 MV. The penumbrae at 3 depths in each beam ͑in g/cm 2 ͒, 1.99 ͑d max , 10 MV only͒, 3.29 ͑d max , 20 MV only͒, 9.79 and 19.79, agree with ionization chamber measurements to better than 1 mm. Possible causes for the discrepancy between calculations and measurements are analyzed and discussed in detail.
Monte Carlo commissioning of radiotherapy LINAC-Introducing an improved methodology
2020
Purpose Monte Carlo (MC) commissioning of medical linear accelerator (LINAC) is a time-consuming process involving a comparison between measured and simulated cross beam/lateral profiles and percentage depth doses (PDDs) for various field sizes. An agreement between these two data sets is sought by trial and error method while varying the incident electron beam parameters, such as electron beam energy or width, etc. This study aims to improve the efficiency of MC commissioning of a LINAC by assessing the feasibility of using a limited number of simulated PDDs. Materials and methods Using EGSnrc codes, a Varian Clinac 2100 unit has been commissioned for 6 MV photon beam, and a methodology has been proposed to identify the incident electron beam parameters in a speedier fashion. Impact of voxel size in 3-dimensions and cost functions used for comparison of the measured and simulated data have been investigated along with the role of interpolation. Results A voxel size of 1 × 1×0.5 cm3...