A comparison of Monte Carlo simulation with experimental dosimetric techniques for a 6 MV stereotactic radiotherapy unit (original) (raw)
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Monte Carlo simulations for dosimetric verification in photon and electron beam radiotherapy
To you, Valter, for being always close even a thousand miles of distance away. We can shine! "Obrigada por teres acreditado sempre no meu valor e me teres feito perceber que posso brilhar". And, finally, I cannot finish my acknowledgments without thanking to my family who constantly supported me with their love and allowed me to complete this work. This thesis is dedicated to them. "A mi familia por la fuerza y el cariño que me regalaron durante esta fase de mi vida. Papá, mamá, Carlos y abuelos, siempre estuvisteis presentes en mi mente y en mi corazón a pesar de la distancia. Luchasteis por hacer realidad mis sueños y nunca tendré amor suficiente para compensar todo aquello que hicisteis por mí. Esta tesis es vuestra."
Physics in Medicine and Biology, 2012
The quality assurance of stereotactic radiotherapy and radiosurgery treatments requires the use of small-field dose measurements that can be experimentally challenging. This study used Monte Carlo simulations to establish that PAGAT dosimetry gel can be used to provide accurate, high-resolution, three-dimensional dose measurements of stereotactic radiotherapy fields. A small cylindrical container (4 cm height, 4.2 cm diameter) was filled with PAGAT gel, placed in the parietal region inside a CIRS head phantom, and irradiated with a 12 field stereotactic radiotherapy plan. The resulting three-dimensional dose measurement was read out using an optical CT scanner and compared with the treatment planning prediction of the dose delivered to the gel during the treatment. A BEAMnrc/DOSXYZnrc simulation of this treatment was completed, to provide a standard against which the accuracy of the gel measurement could be gauged. The three dimensional dose distributions obtained from Monte Carlo and from the gel measurement were found to be in better agreement with each other than with the dose distribution provided by the treatment planning system's pencil beam calculation. Both sets of data showed close agreement with the treatment planning system's dose distribution through the centre of the irradiated volume and substantial disagreement with the treatment planning system at the penumbrae. The Monte Carlo calculations and gel measurements both indicated that the treated volume was up to 3 mm narrower, with steeper penumbrae and more variable out-of-field dose, than predicted by the treatment planning system. The Monte Carlo simulations allowed the accuracy of the PAGAT gel dosimeter to be verified in this case, allowing PAGAT gel to be utilised in the measurement of dose from stereotactic and other radiotherapy treatments, with greater confidence in the future. ‡ Experimental aspects of this work were originally presented at the Engineering and
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% ...
Application of a Monte Carlo linac model in routine verifications of dose calculations
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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...
Validation of Monte Carlo Model for Dose Evaluation outside the Treatment Field for Siemens 6MV Beam
Iranian Journal of Medical Physics, 2019
Introduction: There has been a concern about the unintended doses to critical structures outside the treatment field because of the increased risk of radiation-induced second cancer and the late effects following radiotherapy treatments. Today, Monte Carlo (MC) simulation is considered the most accurate and detailed method for dose calculations in different areas of medical physics. Materials and Methods: Geant4/GATE code was used to create a MC model of 6MV Siemens Primus linac. Measurements were taken in water phantom using an ion chamber to validate the MC model. Dose profiles (DPs) outside the treatment field at 1.5 (dmax), 5.0 and10.0cm depths for field sizes from 5×5 to 20×20cm2 were measured. Out-of-field percent depth dose (PDD) curves at 0.0, 5.0 and 7.5cm off axis for field size 10×10cm2 were investigated for both measurements and simulation, while out-of-field PDDs from 10 to15cm off axis for field size 10×10cm2 were studied by simulation only. The comparison between the ...
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Physics in Medicine and Biology, 2012
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International Journal of Radiation Oncology*Biology*Physics, 1990
The dosimetry of small photon beams used for stereotactic radiosurgery was investigated using Monte Carlo simulation, convolution calculations, and measurements. A Monte Carlo code was used to simulate radiation transport through a linear accelerator to produce and score energy spectrum and angular distribution of 6 MV bremsstrahlung photons exiting from the accelerator treatment head. These photons were then transported through a stereotactic collimator system and into a water phantom placed at isocenter. The energy spectrum was also used as input for the convolution method of photon dose calculation. Monte Carlo and convolution results were compared with the measured data obtained using an ionization chamber, a diode, and film.
Monte Carlo commissioning of radiotherapy LINAC-Introducing an improved methodology
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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...
A Hybrid Approach for Fast Simulation of Dose Deposition in Stereotactic Synchrotron Radiotherapy
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A hybrid approach was developed to compute the dose deposited in cancerous and healthy tissues during stereotactic synchrotron radiation therapy treatment. The proposed approach divides the computation into two parts: (1) the dose deposited by primary radiation (coming directly from the incident X-ray beam) is calculated using a deterministic algorithm based on ray casting, optimized for transport in voxelized geometries; (2) the dose deposited by secondary radiation (Rayleigh and Compton scattering, fluorescence) is computed using a hybrid algorithm combining Monte Carlo and deterministic calculations. In the Monte Carlo part, a set of scattering and fluorescence events occurring in the patient is determined. These events are further processed in a deterministic way, which considerably improves the statistics of the final dose map. The results obtained in test cases are compared to those obtained with the Monte Carlo method alone (Geant4 and MCNPX codes) and found to be in excellent agreement. The proposed simulation scheme makes it possible to simulate dose maps with a single PC, featuring computation time and statistical fluctuations substantially reduced in comparison with full Monte Carlo simulations.