Browsing by Author "Rodríguez Mongua, José Luis"

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    A simple analytical model for a fast 3D assessment of peripheral photon dose during coplanar isocentric photon radiotherapy
    (2022) Sánchez Nieto, Beatriz; López Martínez, Ignacio N.; Rodríguez Mongua, José Luis; Espinoza Bornscheuer, Ignacio Guillermo
    Considering that cancer survival rates have been growing and that nearly two-thirds of those survivors were exposed to clinical radiation during its treatment, the study of long-term radiation effects, especially secondary cancer induction, has become increasingly important. To correctly assess this risk, knowing the dose to out-of-field organs is essential. As it has been reported, commercial treatment planning systems do not accurately calculate the dose far away from the border of the field; analytical dose estimation models may help this purpose. In this work, the development and validation of a new three-dimensional (3D) analytical model to assess the photon peripheral dose during radiotherapy is presented. It needs only two treatment-specific input parameter values, plus information about the linac-specific leakage, when available. It is easy to use and generates 3D whole-body dose distributions and, particularly, the dose to out-of-field organs (as dose–volume histograms) outside the 5% isodose for any isocentric treatment using coplanar beams [including intensity modulated radiotherapy and volumetric modulated arc therapy (VMAT)]. The model was configured with the corresponding Monte Carlo simulation of the peripheral absorbed dose for a 6 MV abdomen treatment on the International Comission on Radiological Protection (ICRP) 110 computational phantom. It was then validated with experimental measurements using thermoluminescent dosimeters in the male ATOM anthropomorphic phantom irradiated with a VMAT treatment for prostate cancer. Additionally, its performance was challenged by applying it to a lung radiotherapy treatment very different from the one used for training. The model agreed well with measurements and simulated dose values. A graphical user interface was developed as a first step to making this work more approachable to a daily clinical application.
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    Determinación de dosis absorbida periférica a través de simulaciones Monte Carlo : evaluación de los algoritmos de cálculo en el planificador comercial Monaco®
    (2018) Rodríguez Mongua, José Luis; Dörner Yaksic, Edgardo Andrés; Pontificia Universidad Católica de Chile. Facultad de Física
    Se ha realizado la simulación Monte Carlo en EGSnrc del acelerador lineal Axesse de Elekta para la obtención de distribuciones de dosis tanto dentro como fuera del campo de radiación de un haz de 6 MV. Dicha simulación ha sido validada por comparación con medidas experimentales. Posteriormente, el modelo Monte Carlo de EGSnrc del acelerador fue aplicado a la evaluación del comportamiento de los algoritmos Collapsed Cone y Monte Carlo de Monaco® en el escenario de una planificación clínica de un tratamiento de pulmón con tres campos sobre el maniquí computarizado masculino del ICRP110. Para lograr este objetivo hubo que transformar el formato original del maniquí ICRP en otro compatible con EGSnrc y con el DICOM que admite el sistema de planificación comercial, así como segmentar las estructuras para el cálculo de la dosis a órgano. La comparación de los resultados se realizó a partir de diversas métricas derivadas de los histogramas dosis volumen. Se encontró que la simulación Monte Carlo de EGSnrc para estimación de dosis periférica, debe ser realizada sin el uso de técnicas de reducción de varianza como el DBS puesto que esto altera de forma importante el computo de dosis fuera del campo. Los resultados obtenidos revelan que Collapsed Cone infraestima la dosis en un 40% cercano al borde del campo (arrastrando la falta de veracidad del sistema dosimétrico empleado en el comisionamiento) y que ambos algoritmos pueden llegar a subestimar la dosis en órganos alejados del borde del campo en más de un 80%. Sin embargo, en general Collapsed Cone reporta valores más cercanos al Monte Carlo de EGSnrc excepto en puntos muy alejados del campo de tratamiento y alineados con el isocentro. El hecho de que Collapsed Cone tenga un mejor comportamiento general puede deberse a que el Monte Carlo de Monaco fue optimizado para tratamientos con modulación de la fluencia.
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    Study of out-of-field dose in photon radiotherapy: A commercial treatment planning system versus measurements and Monte Carlo simulations
    (2020) Sánchez Nieto, Beatriz; Medina Ascanio, Karem Nathalie; Rodríguez Mongua, José Luis; Doerner, Edgardo; Espinoza Bornscheuer, Ignacio Guillermo
    Purpose: An accurate assessment of out-of-field dose is necessary to estimate the risk of second cancer after radiotherapy and the damage to the organs at risk surrounding the planning target volume. Although treatment planning systems (TPSs) calculate dose distributions outside the treatment field, little is known about the accuracy of these calculations. The aim of this work is to thoroughly compare the out-of-field dose distributions given by two algorithms implemented in the Monaco TPS, with measurements and full Monte Carlo simulations. Methods: Out-of-field dose distributions predicted by the collapsed cone convolution (CCC) and Monte Carlo (MCMonaco) algorithms, built into the commercially available Monaco version 5.11 TPS, are compared with measurements carried out on an Elekta Axesse linear accelerator. For the measurements, ion chambers, thermoluminescent dosimeters, and EBT3 film are used. The BEAMnrc code, built on the EGSnrc system, is used to create a model of the Elekta Axesse with the Agility collimation system, and the space phase file generated is scored by DOSXYZnrc to generate the dose distributions (MCEGSnrc). Three different irradiation scenarios are considered: (a) a 10 x 10 cm(2)field, (b) an IMRT prostate plan, and (c) a three-field lung plan. Monaco's calculations, experimental measurements, and Monte Carlo simulations are carried out in water and/or in an ICRP110 phantom. Results: For the 10 x 10 cm(2)field case, CCC underestimated the dose, compared to ion chamber measurements, by 13% (differences relative to the algorithm) on average between the 5% and the approximate to 2% isodoses. MC(Monaco)underestimated the dose only from approximately the 2% isodose for this case. Qualitatively similar results were observed for the studied IMRT case when compared to film dosimetry. For the three-field lung plan, dose underestimations of up to approximate to 90% for MC(Monaco)and approximate to 60% for CCC, relative to MC(EGSnrc)simulations, were observed in mean dose to organs located beyond the 2% isodose. Conclusions: This work shows that Monaco underestimates out-of-field doses in almost all the cases considered. Thus, it does not describe dose distribution beyond the border of the field accurately. This is in agreement with previously published works reporting similar results for other TPSs. Analytical models for out-of-field dose assessment, MC simulations or experimental measurements may be an adequate alternative for this purpose.