Accurate model of photon beams as a tool for commissioning and quality assurance of treatment planning calculations (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...
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 photon beam modeling and commissioning for radiotherapy dose calculation algorithm
Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), 2014
The aim of the present work was a Monte Carlo verification of the Multi-grid superposition (MGS) dose calculation algorithm implemented in the CMS XiO (Elekta) treatment planning system and used to calculate the dose distribution produced by photon beams generated by the linear accelerator (linac) Siemens Primus. The BEAMnrc/DOSXYZnrc (EGSnrc package) Monte Carlo model of the linac head was used as a benchmark. In the first part of the work, the BEAMnrc was used for the commissioning of a 6 MV photon beam and to optimize the linac description to fit the experimental data. In the second part, the MGS dose distributions were compared with DOSXYZnrc using relative dose error comparison and γ-index analysis (2%/2 mm, 3%/3 mm), in different dosimetric test cases. Results show good agreement between simulated and calculated dose in homogeneous media for square and rectangular symmetric fields. The γ-index analysis confirmed that for most cases the MGS model and EGSnrc doses are within 3% ...
Atom Indonesia, 2021
In radiotherapy, high energy ionizing radiation, such as X-rays, gamma rays and electron beams, is used. The dose in the tissue is often approached with the dose in the medium of the body which is 80 % of human soft tissue. It is often difficult to determine the dose because the interaction of materials in a medium is very random. Measurement is also quite difficult because there are almost no detectors that are tissue equivalent. Measurement using an ion chamber requires a lot of correction to obtain a dose in the tissue, which is done using phantom and not directly in humans. This research aimed to compare the absorbed dose between modelling using Monte Carlo simulation and experiments. The simulation of dose distribution produced by a 6 MV medical linear accelerator has been performed using BEAMnrc code running on Linux-based 2 processor system arranged in parallel. BEAMnrc was used to model and simulate the linac head with an SSD of 100 cm and Field size of 10x10 cm 2. A phase-space file is obtained as input to a DOSXYnrc code to produce Percent Depth Dose (PDD) in water and polymethyl methacrylate (PMMA) phantoms. New particles formed (electrons: 0.2 %, photon: 0.17 %; and positron: 0.08 %) were far from the contamination threshold of 2 %. The range of the correction factor of the depth of a maximum dose compared to the experimental data was 0.04-0.15.
Application of a Monte Carlo linac model in routine verifications of dose calculations
Nucleus, 2015
The analysis of some parameters of interest in radiotherapy Medical Physics based on an experimentally validated Monte Carlo model of an Elekta Precise lineal accelerator was performed for 6 and 15 MV photon beams. The simulations were performed using the EGSnrc code. As reference for simulations, the values of the previously obtained optimal beam parameters (energy and FWHM) were used. Deposited dose calculations in water phantoms were done, on typical complex geometries commonly are used in acceptance and quality control tests, such as irregular and asymmetric fi elds. Parameters such as MLC scatter, maximum opening or closing position, and the separation between them were analyzed from calculations in water. Similarly simulations were performed on phantoms obtained from CT studies of real patients, making comparisons of the dose distribution calculated with EGSnrc and the dose distribution obtained from the computerized treatment planning systems used in routine clinical plans. A...
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.
Progress in Medical Physics
Versa HD TM. The beam characteristics of both machines are similar because of the same Agility TM MLC Model. We compared measured beam data calculated using the Elekta treatment planning system, Monaco ® , for each institute. Methods: Beam of the commissioning Elekta linear accelerator were measured in two independent institutes. After installing the beam model based on the measured beam data into the Monaco ® , Monte Carlo (MC) simulation data were generated, mimicking the beam data in a virtual water phantom. Measured beam data were compared with the calculated data, and their similarity was quantitatively evaluated by the gamma analysis. Results: We compared the percent depth dose (PDD) and off-axis profiles of 6 MV photon and 6 MeV electron beams with MC calculation. With a 3%/3 mm gamma criterion, the photon PDD and profiles showed 100% gamma passing rates except for one inplane profile at 10 cm depth from VMTH. Gamma analysis of the measured photon beam off-axis profiles between the two institutes showed 100% agreement. The electron beams also indicated 100% agreement in PDD distributions. However, the gamma passing rates of the off-axis profiles were 91%-100% with a 3%/3 mm gamma criterion. Conclusions: The beam and their comparison with MC calculation for each institute showed good performance. Although the measuring tools were orthogonal, no significant difference was found.
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 treatment planning for photon and electron beams
2007
During the last few decades, accuracy in photon and electron radiotherapy has increased substantially. This is partly due to enhanced linear accelerator technology, providing more flexibility in field definition (e.g. the usage of computercontrolled dynamic multileaf collimators), which led to intensity modulated radiotherapy (IMRT). Important improvements have also been made in the treatment planning process, more specifically in the dose calculations. Originally, dose calculations relied heavily on analytic, semi-analytic and empirical algorithms. The more accurate convolution/superposition codes use pre-calculated Monte Carlo dose ''kernels'' partly accounting for tissue density heterogeneities. It is generally recognized that the Monte Carlo method is able to increase accuracy even further. Since the second half of the 1990s, several Monte Carlo dose engines for radiotherapy treatment planning have been introduced. To enable the use of a Monte Carlo treatment planning (MCTP) dose engine in clinical circumstances, approximations have been introduced to limit the calculation time. In this paper, the literature on MCTP is reviewed, focussing on patient modeling, approximations in linear accelerator modeling and variance reduction techniques. An overview of published comparisons between MC dose engines and conventional dose calculations is provided for phantom studies and clinical examples, evaluating the added value of MCTP in the clinic. An overview of existing Monte Carlo dose engines and commercial MCTP systems is presented and some specific issues concerning the commissioning of a MCTP system are discussed. r
Modeling of a Linear Accelerator Saturne 43 and Study of Photon Dose Distributions
— BEAMnrc is a widely used Monte Carlo (MC) code for simulation of photon and electron transport in the radiotherapy area. The aim of this study was to ameliorate a technique that changing the initial properties of incident electron beam as purpose to have the difference between calculated and measured values of doses produced by the linear accelerator (linac) Saturne 43 machine to be within 1.5%/1mm. We changed the initial electron energy and full width half maximum (FWHM) of the radius of the electron beam incident on the tungsten target to find the percentage depth dose(PDD), dose profile(DP) curves, the tissue-phantom ratio TPR 20/10 , the energy fluence distribution and angular distribution for a square field size 10×10 cm 2. The value of TPR 20/10 agrees well with the publisher related works, also w e c o u l d f i n d q u a n t i t a t i v e l y g o o d r e s u l t s w h i c h a g r e e w e l l w i t h experimental PDD and lateral profiles at 10 cm depth. M o r e o v e r , w e c o u l d r e d u c e the discrepancy between measured and calculated data photon dose distributions to be within 1.5%/1mm in the gamma index method for the energy 11.8 MeV and FWHM= 0.07 cm. Using BEAMnrc code on modeling and simulation of the treatment head of the Saturne 43 machine was successfully done altering the initial properties of electron source. That shows the efficacy and accuracy of the technique used in this paper to obtain the discrepancy within 1.5%/1 mm.