Specialized techniques that make use of small field dosimetry are common practice in today's clin... more Specialized techniques that make use of small field dosimetry are common practice in today's clinics. These new techniques represent a big challenge to the treatment planning systems due to the lack of lateral electronic equilibrium. Because of this, the necessity of planning systems to overcome such difficulties and provide an accurate representation of the true value is of significant importance. Pinnacle 3 is one such planning system. During the IMRT optimization process, Pinnacle 3 treatment planning system allows the user to specify a minimum segment size which results in multiple beams composed of several subsets of different widths. In this study, the accuracy of the engine dose calculation, collapsed cone convolution superposition algorithm (CCCS) used by Pinnacle 3 , was quantified by Monte Carlo simulations, ionization chamber, and Kodak extended dose range film (EDR2) measurements for 11 SBRT lung patients. Lesions were < 3.0 cm in maximal diameter and < 27.0 cm 3 in volume. The Monte Carlo EGSnrc\BEAMnrc and EGS4\MCSIM were used in the comparison. The minimum segment size allowable during optimization had a direct impact on the number of monitor units calculated for each beam. Plans with the smallest minimum segment size (0.1 cm 2 to 2.0 cm 2) had the largest number of MUs. Although PTV coverage remained unaffected, the segment size did have an effect on the dose to the organs at risk. Pinnacle 3-calculated PTV mean doses were in agreement with Monte Carlo-calculated mean doses to within 5.6% for all plans. On average, the mean dose difference between Monte Carlo and Pinnacle 3 for all 88 plans was 1.38%. The largest discrepancy in maximum dose was 5.8%, and was noted for one of the plans using a minimum segment size of 1.0 cm 2. For minimum dose to the PTV, a maximum discrepancy between Monte Carlo and Pinnacle 3 was noted of 12.5% for a plan using a 6.0 cm 2 minimum segment size. Agreement between point dose measurements and Pinnacle 3-calculated doses were on average within 0.7% in both phantoms. The profiles show a good agreement between Pinnacle 3 , Monte Carlo, and EDR2 film. The gamma index and the isodose lines support the result.
ABSTRACT We show that it is possible for chaotic systems to display the main features of coherenc... more ABSTRACT We show that it is possible for chaotic systems to display the main features of coherence resonance. In particular, we show that a Chua model, operating in a chaotic regime and in the presence of noise, can exhibit oscillations whose regularity is optimal for some intermediate value of the noise intensity. We nd that the power spectrum of the signal develops a peak at nite frequency at intermediate values of the noise. These are all signatures of coherence resonance. We also experimentally study a Chua circuit and corroborate the above simulation results. Finally, we analyze a simple model composed of two separate limit cycles which still exhibits coherence resonance, and show that its behavior is qualitatively similar to that of the chaotic Chua system.
En este artículo se presenta el problema de buscar un objeto sumergido utilizando un vehículo sub... more En este artículo se presenta el problema de buscar un objeto sumergido utilizando un vehículo submarino autoguiado, y en caso de que el mismo se pierda, utilizar una estrategia de recuperación. La solución propuesta, basada en una máquina de estados implementada en lenguaje C++ y corriendo en un sistema GNU/LINUX, se desempeñó correctamente en simulación. Para realizar estas pruebas debió desarrollarse un ambiente de simulación que también se describe brevemente. Todo el diseño fue hecho teniendo presente la posibilidad de ser trasladado a un submarino real. Los mencionados resultados, como así también unas conclusiones preliminares y líneas de trabajo futuro, completan el trabajo.
ANTECEDENTES: desde 1991 la técnica endovascular se ha aplicado con éxito en el manejo de los ane... more ANTECEDENTES: desde 1991 la técnica endovascular se ha aplicado con éxito en el manejo de los aneurismas de aorta infrarrenal, y se ha perfeccionado de manera tal que rápidamente se ha convertido en una alternativa para pacientes de alto riesgo para la cirugía convencional.
Arteria carótida y placa "carótida un órgano" Carotid artery and plaque. "carotid: an organ" Juan... more Arteria carótida y placa "carótida un órgano" Carotid artery and plaque. "carotid: an organ" Juan G. Barrera, MD.; Ligia C. Mateus, MD.; José F. Saaibi, MD.; Carlos S. Balestrini, MD.; Jaime Calderón, MD.; Marisol Carreño, MD.; Víctor R. Castillo, MD.; Camilo Pizarro, MD.; Omar F. Gomezese, MD.; Fredy López, MD.; Ángel M. Cháves, MD.; Carlos A. Luengas, MD.; Oscar Calvo, MD.; Rafael Reyes, MD.; Fabio M. Aguilera, MD.; Jorge E. Bayter, MD.; Leonardo Salazar, MD.; Jimmy Muñoz, MD. Floridablanca, Santander, Colombia.
En comparación con el tratamiento convencional, la terapia endovascular en aneurisma de aorta tor... more En comparación con el tratamiento convencional, la terapia endovascular en aneurisma de aorta torácica, presenta los mejores resultados, por lo que se convierte en el tratamiento de elección para la patología de aorta torácica descendente endovascular, por su baja ...
Endarterectomía carotídea en pacientes sintomáticos y asintomáticos: resultados de morbi-mortalidad desde 1998 hasta 2005
Revista Colombiana De Cardiologia, Dec 1, 2007
Antecedentes: el accidente cerebrovascular es la tercera causa de muerte y probablemente la causa... more Antecedentes: el accidente cerebrovascular es la tercera causa de muerte y probablemente la causa más importante de discapacidad a largo plazo. La tasa de mortalidad está entre 15% y 35% con el primer ataque y se eleva a 65% para los accidentes ...
En estos momentos es posible hacer recomendaciones sobre las indicaciones de la endarterectomía c... more En estos momentos es posible hacer recomendaciones sobre las indicaciones de la endarterectomía carotídea, basadas en los ensayos clínicos publicados y en la revisión de grandes series quirúrgicas. Las indicaciones para la cirugía dependerán del grado de estenosis y de la ...
Stochastic and coherence resonances appear in nonlinear systems subjected to an external source o... more Stochastic and coherence resonances appear in nonlinear systems subjected to an external source of noise and are characterized by a maximum response at the optimal value of the noise intensity. This paper shows experimentally that it is possible to observe them in a chaotic system. To this end we have analysed an electronic Chua circuit running in the chaotic regime and added noise to its dynamics. In the case of coherence resonance, we observe an optimal periodicity for the jumps between chaotic attractors, whereas in the case of stochastic resonance we observe a maximum in the signal-to-noise ratio at the frequency of an external sinusoidal perturbation.
Experimental results on smooth path tracking with application to pipe surveying on inexpensive AUV
2008 Ieee Rsj International Conference on Intelligent Robots and Systems, 2008
This paper details the development aspects of a low cost AUV autonomous, designed for autonomous ... more This paper details the development aspects of a low cost AUV autonomous, designed for autonomous pipline inspections, describing: hardware, software and control aspects. The article details three of the mains stages of the project, that have been already achieved: (a) the simulation results of Lyapunov based path planning of torpedo shaped AUV on pipe searching; (b) the construction details of
Guiado y Control del Vehículo Autónomo Submarino CORMORÁN combinando acción por adelanto y lógica difusa
Resumen— Este trabajo describe el diseño de las estrategias de guiado y control de un robot de ba... more Resumen— Este trabajo describe el diseño de las estrategias de guiado y control de un robot de bajo costo para la observación marítima, llamado CORMORÁN. Dicha plataforma es un híbrido entre un vehículo submarino autónomo (AUV) y un vehículo de superficie autónomo (ASV). CORMORÁN se mueve ligeramente por debajo de la superficie del agua siguiendo una trayectoria previamente fijada. En
Tratamiento de aorta abdominal e ilíacas con técnica endovascular: Experiencia quirúrgica
Revista Colombiana De Cardiologia, Aug 1, 2007
Juan G. Barrera, MD.(1); Ligia C. Mateus, MD.(1); Marisol Carreño, MD.(1); Jorge E. Bayter, MD.(1... more Juan G. Barrera, MD.(1); Ligia C. Mateus, MD.(1); Marisol Carreño, MD.(1); Jorge E. Bayter, MD.(1); José F. Saaibi, MD.(1); Carlos S. Balestrini, MD.(1); Melquisedec Gutiérrez, MD.(1); Jaime Calderón, MD.(1); Víctor R. Castillo, MD.(1); Oscar F. Calvo, MD.(2); Jimmy G. Muñoz, ...
Conference Record of the 1991 IEEE Particle Accelerator Conference, 1991
The South Hall Ring (SHR) under construction at the MIT-Bates Linear Accelerator Center will prov... more The South Hall Ring (SHR) under construction at the MIT-Bates Linear Accelerator Center will provide a high duty factor electron beam and internal target capability for nuclear research. For proper operation of the pulse stretcher ring, a large number of highly stable power supplies are required. Most of these supplies will be powering multipole magnets at currents ranging from 10 A. to 155A. with the output power between 1.2 and 11.5 KW. The high stability specifications of these supplies, better than 25 PPM of the 1.1 GFV current value, including temperature drift and ripple, normally suggests the purchase of custom manufactured supplies. However, due to the costs of custom supplies, we tested the feasibility of upgrading commercial supplies with an external controller to improve the current regulation from a typical value of 200 PPM to better than 25 PPM.
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