EURADOS intercomparison exercise on Monte Carlo modelling of a medical linear accelerator (original) (raw)
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Monte Carlo simulation of a medical linear accelerator for radiotherapy use
Radiation Protection Dosimetry, 2006
In order to simulate radiation transport, various algorithms, codes, and programs have been developed. In this study Monte Carlo N-particle code is used to simulate a medical electron linear accelerator gantry for research purposes. Detailed geometry of the LINAC head and water phantom are modeled and simulated for calculations. Analyses are made for filtered and flattening filter-free (FFF) systems. Percent depth dose and dose profile measurements are calculated with Monte Carlo simulations and compared with experimental and theoretical values for quality assurance of the model. Flux, dose, and spectrum analyses are performed for filtered and FFF systems separately. In this study, it was aimed to run the linear accelerator in a computer environment for different purposes, and this aim was achieved.
Physics in medicine and biology, 2009
There is a serious and growing concern about the increased risk of radiation-induced second cancers and late tissue injuries associated with radiation treatment. To better understand and to more accurately quantify non-target organ doses due to scatter and leakage radiation from medical accelerators, a detailed Monte Carlo model of the medical linear accelerator is needed. This paper describes the development and validation of a detailed accelerator model of the Varian Clinac operating at 6 and 18 MV beam energies. Over 100 accelerator components have been defined and integrated using the Monte Carlo code MCNPX. A series of in-field and out-of-field dose validation studies were performed. In-field dose distributions calculated using the accelerator models were tuned to match measurement data that are considered the de facto 'gold standard' for the Varian Clinac accelerator provided by the manufacturer. Field sizes of 4 cm × 4 cm, 10 cm × 10 cm, 20 cm × 20 cm and 40 cm × 40 cm were considered. The local difference between calculated and measured dose on the percent depth dose curve was less than 2% for all locations. The local difference between calculated and measured dose on the dose profile curve was less than 2% in the plateau region and less than 2 mm in the penumbra region for all locations. Out-of-field dose profiles were calculated and compared to measurement data for both beam energies for field sizes of 4 cm × 4 cm, 10 cm × 10 cm and 20 cm × 20 cm. For all field sizes considered in this study, the average local difference between calculated and measured dose for the 6 and 18 MV beams was 14 and 16%, respectively. In addition, a method for determining neutron contamination in the 18 MV operating model was validated by comparing calculated in-air neutron fluence with reported calculations and measurements. The average difference between calculated and measured neutron fluence was 20%. As one of the most detailed accelerator models for both in-field and outof-field dose calculations, the model will be combined with anatomically realistic computational patient phantoms into a computational framework to calculate non-target organ doses to patients from various radiation treatment plans.
Journal of B.U.ON.: official journal of the Balkan Union of Oncology
Purpose: To compare Monte Carlo simulation with conventional dosimetry techniques for stereotactic radiotherapy (SRT), since accurate dosimetry of narrow photon beams is very complicated and has often been questioned, mainly due to the lack of lateral electronic equilibrium and uncertainty in beam energy in terms of steep dose gradients. Materials and methods: In this work a Monte Carlo (MC, EGS4) simulation for dosimerty study was performed for the 6MV home made SRT unit of the University Hospital of Patras (Hellas). The results were compared with conventional small field dosimetry techniques such as ionization chamber, TLD's, and films (conventional and radiochromic). Hence, a comparison of many of the dosimetric techniques currently being used in small field dosimetry was attempted. Results: It was shown that all techniques are in reasonable agreement (within ± 2%) and that Monte Carlo can be used as a reliable reference for the dosimetry of the SRT beams, especially where lateral electronic equilibrium does not exist, as long as accurate simulation can be achieved. Conclusion: This study is only limited by the insurance of accurate simulation of the linear accelerator, which can be a difficult task since it is limited by the availability of the manufacturer's designs and the availability of computers and computer time for adequate runs, but it could become a useful tool for Monte Carlo simulations, as it contains detailed analysis of the run parameters and component modules selection.
Monte Carlo Estimation of Dose in Heterogeneous Phantom Around 6MV Medical Linear Accelerator
Advances in Science, Technology and Engineering Systems Journal
In this work, we completed a validation of the Varian Clinac IX equipped with the High Definition Multi-Leaf Collimator (HD 120 MLC) instead of the removable jaws, using GATE Monte Carlo Platform version 8.2. We validated the multileaf collimator (MLC) geometry by simulating two dosimetric functions (Percentage Depth Dose (PDD) and Dose Profile (DP)), for 6MV photon beam energy and different field sizes (3x3, 4x4, 6x6, 8x8, 10x10, 12x12, 15x15, and 20x20 cm²). We then compared the results with measurements realized with two detectors, namely the cylindrical ionization chamber and the micro-diode PTW silicon. By applying the Relative Dose Difference method (RDD), we noted a less than 2% and 1% agreement for the field sizes (10x10, 12x12, 15x15, 20x20 cm²) and (3x3, 4x4, 6x6, 8x8 cm²) respectively. Moreover, to evaluate the relevance of Monte Carlo method in a heterogeneous media, particularly in small field sizes (1x1, 2x2, 3x3 cm²), we have simulated three clinical studies based on the Physical Test Objects (PTOs) that are the equivalent slabs of lung and bone included in a water phantom. We noticed that the simulated PDDs exhibit two significant irregularities in the interface between water and lung. To eliminate these phenomena, we have used the "setMaxStepSizeInRegion" parameter implemented in GATE. We also noticed an important difference of 5% corresponding to the small field sizes, between homogeneous and heterogeneous simulated PDDs. We used the RDD method in this case as well. Moreover, we observed a difference between 1-4% between the simulated PDDs and the calculated ones by ECLIPSE Treatment Planning System (TPS). These results indicate that GATE (8.2) is useful in dosimetry with heterogeneous situations as well such as bone and lung.
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...
Brazilian Journal of Physics, 2005
Intra-operative radiotherapy (IORT) using electron beams has demonstrated to be a good alternative as part of the breast-conserving surgery. Besides, as the computer processing capacity has been increasing along the years, it has become a potential auxiliary tool in radiotherapy treatment planning. In this work these streams are merged together: simulations were performed by different Monte Carlo radiation transport codes (EGS4 and MCNP in its releases 4C and 5) in an attempt to not only examine the efficacy of Al and Pb discs used in IORT procedures to protect critical regions but also to compare the performance of the forementioned codes.
2010
In this work, the accuracy of the implementation of the Macro Monte Carlo electron dose calculation algorithm into the radiation therapy treatment planning system Eclipse is evaluated. This implementation -called eMC -uses a particle source based on the Rotterdam Initial Phase-Space model. A three-dimensional comparison of eMC calculated dose to dose distributions resulting from full treatment head simulations with the Monte Carlo code package EGSnrc is performed using the 'virtual accelerator' approach. Calculated dose distributions are compared for a homogeneous tissue equivalent phantom and a water phantom with air and bone inhomogeneities. The performance of the eMC algorithm in both phantoms can be considered acceptable within the 2%/2 mm Gamma index criterion. A systematic underestimation of dose by the eMC algorithm within the air inhomogeneity is found.
A Comparison Between GATE and MCNPX Monte Carlo Codes in Simulation of Medical Linear Accelerator
2014
Radiotherapy dose calculations can be evaluated by Monte Carlo (MC) simulations with acceptable accuracy for dose prediction in complicated treatment plans. In this work, Standard, Livermore and Penelope electromagnetic (EM) physics packages of GEANT4 application for tomographic emission (GATE) 6.1 were compared versus Monte Carlo N-Particle eXtended (MCNPX) 2.6 in simulation of 6 MV photon Linac. To do this, similar geometry was used for the two codes. The reference values of percentage depth dose (PDD) and beam profiles were obtained using a 6 MV Elekta Compact linear accelerator, Scanditronix water phantom and diode detectors. No significant deviations were found in PDD, dose profile, energy spectrum, radial mean energy and photon radial distribution, which were calculated by Standard and Livermore EM models and MCNPX, respectively. Nevertheless, the Penelope model showed an extreme difference. Statistical uncertainty in all the simulations was <1%, namely 0.51%, 0.27%, 0.27% ...
Monte Carlo techniques in radiation medicine
Physics plays a big role in medicine. In addition to explaining the mechanisms by which the different systems of the body function, physics, especially radiation physics, provides different diagnostic and therapeutic tools. Due to the random nature of interaction of radiation with body, an accurate mean of calculation is needed. Monte Carlo techniques provide this necessary accuracy.The main objective of this work is to highlight the importance of and the facilities provided by Monte Carlo Techniques in the different fields of radiation medicine.This review provides evidence of the importance and significance of application of Monte Carlo calculations in the different disciplines of radiation medicine and demonstrates the use of one of the most commonly used Monte Carlo codes in simulation in radiotherapy.The significance of application and ease of utilization of Monte Carlo codes even with minimum computational knowledge were clearly demonstrated in this work.Monte Carlo codes prov...