RESUMO
Investigations regarding the feasibility, reliability, and accuracy of Fricke gel dosimeter layers for stereotactic radiosurgery are presented. A representative radiosurgery plan consisting of two targets has been investigated. Absorbed dose distributions measured using radiochromic films and gelatin Fricke Gel dosimetry in layers have been compared with dose distributions calculated by using a treatment planning system and Monte Carlo simulations. The different dose distributions have been compared by means of the gamma index demonstrating that gelatin Fricke gel dosimeter layers showed agreements of 100%, 100%, and 93%, with dose and distance tolerances of 2% and 2 mm, with respect to film dosimetry, treatment planning system and Monte Carlo simulations, respectively. The capability of the developed system for three-dimensional dose mapping was shown, obtaining promising results when compared with well-established dosimetry methods. The obtained results support the viability of Fricke gel dosimeter layers analyzed by optical methods for stereotactic radiosurgery.
Assuntos
Corantes Fluorescentes/química , Géis/química , Fenóis/química , Dosímetros de Radiação/normas , Radiocirurgia/métodos , Sulfóxidos/química , Estudos de Viabilidade , Humanos , Método de Monte Carlo , Imagens de Fantasmas , Reprodutibilidade dos TestesRESUMO
Al realizarse estudios sobre muestras óseas para analizar características como dureza, densidad y salud, se suelen utilizar equipamientos que permiten la cuantificación de la densidad electrónica, proporcional a la densidad másica, que se relaciona directamente con la densidad mineral ósea. El test conocido como densitometría ósea se suele realizar con equipos de rayos X, ultrasonido o por medio de la utilización de isótopos radioactivos. Este estudio cuantifica la cantidad mineral ósea por superficie y suele ser utilizado para evaluar, entre otros, riesgos de fracturas o estado de osteoporosis. La técnica de tomografía computada utiliza imágenes bidimensionales de rayos X y métodos de reconstrucción tomográfica implementados en algoritmos computacionales para obtener información de la estructura interna de un objeto, de forma no destructiva. Equipamientos especialmente desarrollados logran obtener imágenes con resolución sub-milimétrica, dando lugar a la técnica conocida como micro-tomografía. La posibilidad de estudiar estructuras óseas con este grado de resolución y obtener imágenes morfológicas tridimensionales con información de la densidad electrónica, presenta una importante opción para estudios específicos sobre, entre otros, crecimiento de hueso y estudios de nuevos componentes que permiten acelerar el crecimiento de tejidos dañados. En el presente trabajo se analizan muestras óseas del cráneo de conejos donde se han dañado determinadas zonas y se han injertado diferentes sustancias tendientes a evaluar respuestas de reparación de tejido óseo. El análisis se realiza a los fines de estudiar la performance de la técnica de micro-tomografía desarrollada en laboratorio con el objetivo de observar su potencialidad en este tipo de estudios y la capacidad de estos análisis en la caracterización de las propiedades físicas de este tipo de muestras.
When performing studies on bone samples aiming at analyzing its physical characteristics such as hardness, density and health, typically it is used to utilize different equipment for the quantification of electron density, which results proportional to mass density, which is directly related to bone mineral density. The test known as bone densitometry is usually done using X-ray equipment, ultrasound or through the utilization of radioactive isotopes. This analysis quantifies the amount of mineral bone on a surface and is usually implemented to assess, among others, risks of fractures or the osteoporosis state in a patient. The computed tomography technique uses two-dimensional X-ray images and tomographic reconstruction methods implemented on computational algorithms to obtain information about the internal structure of an object in a nondestructively way. Specially developed equipment able to obtain images with sub-millimeter resolution, results in the technique known as micro-tomography. The ability to study bone structures at sub-millimeter levels and obtain three-dimensional morphological images with electron density information, presents an important option for specific studies on bone growth and studies on new components that allow the growth of damaged tissues. In this paper rabbits cranium bone samples where certain areas have been damaged and have been filled with different substances specially designed to evaluate repair responses on bone tissue are analyzed. The analysis is performed in order to study the performance of the micro-tomography technique developed in the laboratory in order to observe its potentiality in this type of studies and the ability of these analysis in the characterization of the physical properties of such samples.
Assuntos
Animais , Osso e Ossos/anatomia & histologia , Osso e Ossos/diagnóstico por imagem , Coelhos/anatomia & histologia , Microtomografia por Raio-X , Densidade ÓsseaRESUMO
This work introduces a new, versatile and robust X-ray detector with hemispherical 2π geometry, based on a set of 15 small cylindrical proportional counters located in a hexagonal and pentagonal fullerene C60 pattern, at the same distance from the center (where a sample is placed). The counteranode consists of stainless steel sewing needles with spherical tips measuring approximately 80 µm in diameter. The space between the counters and the sample could contain air, the same gas as the counters or vacuum. This allows a significant increase in the count rates by a factor approximately equal to the number of counters connected. It is shown that an energy resolution of 20% for 5.9 keV photons can be obtained, and a global counting rate of around 10(6)counts/s is achievable by the 15 Needle Anode Proportional Counters (NAPCs) operating in parallel mode, in our setup.
Assuntos
Radiometria/instrumentação , Eletrodos , Desenho de Equipamento , Humanos , Fótons , Radiometria/estatística & dados numéricos , Raios XRESUMO
The Frutillar 82, F nasal 90, F vaginal 90, Puente Alto 77, VMLB 79, and Bio Bio 92 isolates of bovine herpesvirus 1 (BHV-1) from Chile were analysed by Eco RI, Bam HI and Hind III restriction enzymes (RE). The Los Angeles (LA) strain was used as reference. The results indicated that the fingerprints of F nasal 90 and F vaginal 90 were identical to the three RE used, but they were different from the other isolates. Major differences were found for Puente Alto 77 and VMLB 79 isolates with Eco RI, and for Puente Alto 77 with Hind III compared with the other Chilean isolates. It is concluded that Chilean BHV-1 isolates obtained from diverse lesions and geographic locations are genomically different from each other and from the other strains described in the literature.