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- ItemDosimetría cardiaca y correlación con peor sobrevida en pacientes con cáncer de mama(2024) Montoya Janampa, Julio Manuel; Caprile Etchart, Paola F.; Pontificia Universidad Católica de Chile. Facultad de FísicaLa radioterapia (RT) es una herramienta fundamental para combatir el cáncer de mama (CM). Para el año 2020 en Chile, la mayoría de los tratamientos de CM incluyeron RT (Sung et al., 2021). Sin embargo, evidencia reciente sugiere que las altas dosis administradas al corazón y sus subestructuras están asociadas a posibles cardiopatías y pueden resultar en un exceso de mortalidad (Díaz-Gavela et al., 2021; Banfill et al., 2021). El objetivo es estudiar la correlación entre la dosis administrada a diferentes subestructuras cardíacas y la supervivencia en el tiempo, e identificar umbrales de dosis predictivos de mortalidad temprana en una cohorte local de pacientes con CM tras la RT.Se empleó un programa open source (Finnegan et al., 2017) para segmentar automáticamente el corazón, sus cavidades, los grandes vasos, sus válvulas, las arterias coronarias y los nodos de conducción en imágenes CT de planificación para 188 pacientes control y 53 pacientes fallecidas, quienes fueron tratadas con RT curativa para CM en la Red de Salud UC-Christus. Se obtuvieron la dosis media y máxima, equivalente en fracciones de 2 Gy (EQD2), y el histograma de dosis-volumen para cada subestructura y regiones cardíacas combinadas. Además, el score de calcio se estimó utilizando un método de umbralizado (Agatston et al., 1990). Se realizaron análisis de supervivencia usando el score de calcio, la información clínica y los parámetros dosimétricos de las regiones cardíacas.El análisis de regresión multivariado mostró que la dosis máxima en la región cardíaca combinada que incluye los ventrículos bilaterales (Gy), el score de calcio (CAC), la etapa del cáncer T (I/II vs III/IV) y la quimioterapia (sí vs no) fueron factores significativos asociados con la supervivencia a través del tiempo en nuestra cohorte, con hazard ratios de 1,02 (95% CI 1,00-1,03; p = 0,0195), 1,05 (95% CI 1,02-1,07; p < 0,001), 4,66 (95% CI 2,51-8,64; p < 0,001) y 2,31 (95% CI 1,08-4,93; p = 0,0309), respectivamente, mientras que la dosis media cardíaca, V5 y V30 no mostraron significancia. Además, se trazaron curvas de supervivencia Kaplan-Meier para un seguimiento de 5 años, demostrando que la cohorte que recibió una EQD2 máxima en la región combinada superior a 30 Gy mostró una supervivencia más baja (log-rank p = 0,0062).La aplicación de esta metodología en pacientes con CM valida a la dosis máxima en los ventrículos bilaterales como importante predictor de muerte prematura. Se obtuvo una EQD2 máxima de 30 Gy como límite de dosis para futuras investigaciones.Palabras clave: Cáncer de mama, Radioterapia, Cardiotoxicidad
- ItemSuperconductivity in a topological weyl semimetal(2024) Esparza Urrutia, Juan Pablo; Muñoz Tavera, Enrique; Pontificia Universidad Católica de Chile. Instituto de FísicaIn this work, we determine the possible superconducting states produced in a type-I Weyl semimetal under a generic interaction, according to the topological nature of the Cooper pair. Once identified, we study the competition and coexistence between those states. At finite temperature, we find a set of conditions, in terms of the quantum numbers and the angular distribution of the pairing gaps, that needs to be fulfilled in order to produce coexistence of the phases. We also characterize the specific heat, finding the typical lambda transition at each phase transition, in concordance with the literature. At zero temperature, we find generic self-consistent equations for the pairing gaps, written exclusively in terms of the value of its quantum numbers and its angular distribution. Using the examples that our model predicted, we show that in general the phases with different topology coexist in a certain zone of the phase space, in the vicinity of the curve along which the effective couplings for each channels are equal. Finally, in what refers to the topological repulsion mechanism proposed in previous work on the topic, we conclude that a feature needed in order to produce such phenomena is the asymmetry in the position of the Weyl points, codified in the different values of chemical potential at each node.
- ItemTowards the generation of spin defects in hBN monolayer by ion implantation(2023) Zelada Concha, Hugo Ignacio; Maze Ríos, Jerónimo; Pontificia Universidad Católica de Chile. Instituto de FísicaThe controlled creation of single-photon emitters in two-dimensional materials has gained significant attention due to its potential applications in quantum technologies and optoelectronic devices. Hexagonal boron nitride (hBN) is an insulator with exceptional mechanical and electrical properties. It has emerged as a promising material for next-generation electronic devices. However, the controlled introduction of defects into hBN monolayers remains a challenge. This work aims to address this challenge by utilizing ion implantation as a technique (maximum energy of 5 keV ) to generate defects in hBN monolayers on Si/SiO2. Argon ions were accelerated and directed onto the hBN surface in a high vacuum environment (10−8 mbar), and to characterize the possible defects and their potential as single emitters, we employed confocal microscopy and photoluminescence spectroscopy. The confocal microscopy technique allows for precise spatial mapping of the defects, while the spectroscopy provides insights into their optical properties, such as emission wavelength and intensity. The ion dose has not been successfully characterized but, under certain approximations, it has been estimated of the order of 1015 ions/cm2 . Bright spots were observed in implanted areas with energies between 0.5 keV and 1.0 keV and implantation times of less than 30 s. Due to the low photostability, it was decided to coat the monolayer with PMMA, which in some cases reduced the effects of photobleaching, in addition to observing new behaviors of the bright spots, such as blinking. The measured spectra present two peaks, which would represent the PSB and the ZPL, and are separated by approximately 0.15 eV . According to the literature, they would correspond to carbon defects, which would present a spin of 1/2. To corroborate if the observed are SPEs, it is necessary to measure the autocorrelation function g(2), as well as, if it is desired to analyze if they have a non-zero spin, it will be necessary to perform measurements with ODMR.
- ItemCharacterization of ferromagnetic and antiferromagnetic systems using nitrogen-vacancy center relaxometry(2024) Cabezón Heitzer, Ricardo Javier; Rodríguez Suárez, Roberto; Pontificia Universidad Católica de Chile. Instituto de FísicaRelaxometry with nitrogen-vacancy (NV) centers in diamond is an innovative and non-invasive technique that has been increasingly used for characterizing magnetic materials. Because of their exceptional quantum coherence and capability to be manipulated optically, it is possible to measure their relaxation time and, from this quantity, probe physical characteristics of the environment. This technique is the so-called called relaxometry. During the last few years, NV centers have been used for measuring magnetic properties in ferromagnetic materials, and a few times for antiferromagnetic systems with easy-axis anisotropy.In this work, we develop a complete theoretical description of NV center relaxometry for several types of magnetic materials (ferromagnetic and antiferromagnetic systems), we indicate what physical parameters can be measured in each situation, when this technique will experimentally work, and how it depends on the sample anisotropy. We found that relaxation rates using ferromagnetic systems peak at certain values of the external magnetic field, where both NV center and sample resonate simultaneously, something that does not happen when using antiferromagnets because of their high resonance frequency. In this way, NV center relaxometry allows us to extract information about the spin waves of the system. Finally, we discuss prospects to non-intrusively probe magnetic properties and phase transitions in ferrimagnetic systems, in triangular-lattice antiferromagnets, such as Cs2CuCl4 and in 2D materials.
- ItemA critical analysis of Shuryak’s Predictive Radiocarcinogenesis Model(2024) Heumann Schröder, Nicolás Matthias; Sánchez Nieto, Beatriz; Espinoza Bornscheuer, Ignacio Guillermo; Pontificia Universidad Católica de Chile. Instituto de FísicaObjective: To critically analyze, simplify and implement a predictive radiocarcinogenesis model to estimate the risk of secondary cancer after RT which can effectively compare different radiotherapy treatment plans with the aim of having an additional element of information during the decision-making process for the best RT plan.Methodology: A Python software was developed that was able to implement the model proposed by Shuryak et al. (2009). Simplifications and minor corrections were made which allowed for more compactness and more efficient run times. The model was then reparametrized with newer data from the Surveillance, Epidemiology, and End Results Program (SEER) database and several epidemiological studies using Bayesian Inference. Uncertainty propagation studies were then conducted to understand their propagation better. Finally, the model with its new parameters was applied to a selection of prostate plans to determine if it could construct a risk hierarchy.Results: The model was successfully reparametrized with newer data. Although some parameters show significant deviation from Shuryak’s original parameters, they are mostly on the same order of magnitude, and the differences arise likely due to differences in fitted data and the fitting process itself. Shuryak’s model successfully built a risk hierarchy between prostate plans, although it deviated from the more simplistic linear non-threshold BEIR VII model. It was also possible to simplify some complex mathematical equations, both in general and for particular cases, allowing for easier implementation and more efficient run times.Conclusions: Shuryak’s model was successfully reparametrized and implemented, showing potential to become clinically applicable. However, more comparisons between the model’s result and epidemiological data must be made to evaluate its accuracy better, and more concise and complete second primary cancer studies must be used before the model is reliable enough for clinical decision-making.