Effects on the accelerating electron bunches due to the presence of sulfur hexafluoride or air in the linac waveguide.

Sulfur hexafluoride gas (SF6) is used as a dielectric insulator in the acceleration process of certain medical linear accelerator waveguides. Nevertheless, some innovative development and investigation cases require intervention in the linear accelerator or, specifically, on the waveguide, which could affect the sealing of the device. In this regard, vacuum sealing systems can be compromised, affecting the properties of the radiation beams produced. The presence of sulfur hexafluoride or air inside the VARIAN 6/100 waveguide was investigated under different pressure conditions and non-uniform electric fields, adapting Monte Carlo simulation techniques for modeling radiation transport coupled with electric fields. Obtained results indicated the suitability of the proposed approach, while comparisons with theoretical approaches and experimental evidence supported the model's consistency.

Behavioural and physiological responses to salinization and air exposure during the ontogeny of a freshwater South American snail.

Salinization is of global concern, threatening freshwater biodiversity. Salinity tolerance is highly variable and therefore needs to be evaluated on a species-specific basis. An estuarine population of Chilina dombeiana, a freshwater gastropod endemic to Chile and classified as vulnerable, has been recently found in the Biobío River's mouth, suggesting some degree of tolerance to brackish waters. This study evaluated the survival, behaviour (medium preference) and physiology of C. dombeiana when exposed to salinities higher than freshwater, thus elucidating the potential mechanisms used to survive salinization. Chilina dombeiana belongs to the Pulmonate group;, so we evaluated oxygen uptake in air and water, aiming to evaluate emersion as a potential avoidance response to a progressive salinity increase. Complete embryo development was observed for salinities ≤ 16 PSU (practical salinity units) but hatching rates above 50% were only achieved in freshwater (0 PSU). It was also found that salinity had stage-specific effects during embryonic development. In adults, acute exposure to brackish water (12 PSU) caused a decrease in oxygen consumption (compared to freshwater), in the ammonium excretion rates and in the percentage of muscular water content. Although C. dombeiana was able to take up oxygen in both mediums, survival in air decreased over time (days), which correlates with the behavioural preference to remain submerged, even at elevated salinities. Considering the survival of adults and embryos decreased as salinity increased and the lack of an avoidance behaviour or a physiological ability to maintain homeostasis at salinities higher than freshwater, our results suggest this snail could be adversely affected by salinization in the long term. Furthermore, given the ability of C. dombeiana to uptake oxygen in both mediums, it should be considered as a facultative air breather snail, rather than a strictly aquatic species.

Housing Instability, Structural Vulnerability, and Non-Fatal Opioid Overdoses Among People Who Use Heroin in Washington Heights, New York City.

Nationally, opioid overdose remains strikingly persistent among people experiencing homelessness and housing instability. Limited information is available about the characteristics of this phenomenon in economically disadvantaged communities of color. This study sought to evaluate the association between key contextual factors and experiencing a non-fatal opioid overdose among people who use heroin in Washington Heights, New York City. We conducted a cross-sectional survey (N = 101) among participants seeking harm reduction services who reported heroin use in the last three months. Binary logistic regression models examined the association between key social and structural factors and the likelihood of ever experiencing a non-fatal opioid overdose and recently experiencing a non-fatal opioid overdose. The majority of the sample reported housing instability and lived in poverty; almost 42% were homeless. After adjustment, participants who injected heroin were more likely to have ever experienced a non-fatal opioid overdose. Also, younger participants who reported hunger in the last six months were more likely to have experienced a non-fatal opioid overdose in the last three months. Findings suggest the role of structural vulnerability in shaping overdose risk among the participants. Overdose prevention strategies should consider factors of the social and economic environment to mitigate barriers to accessing health and social services within the context of the current opioid crisis.

Fricke gel xylenol orange dosimeter layers for stereotactic radiosurgery: A preliminary approach.

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.

Direct evidence of sex and a hypothesis about meiosis in Symbiodiniaceae.

Dinoflagellates in the family Symbiodiniaceae are obligate endosymbionts of diverse marine invertebrates, including corals, and impact the capacity of their hosts to respond to climate change-driven ocean warming. Understanding the conditions under which increased genetic variation in Symbiodiniaceae arises via sexual recombination can support efforts to evolve thermal tolerance in these symbionts and ultimately mitigate coral bleaching, the breakdown of the coral-Symbiodiniaceae partnership under stress. However, direct observations of meiosis in Symbiodiniaceae have not been reported, despite various lines of indirect evidence that it occurs. We present the first cytological evidence of sex in Symbiodiniaceae based on nuclear DNA content and morphology using Image Flow Cytometry, Cell Sorting and Confocal Microscopy. We show the Symbiodiniaceae species, Cladocopium latusorum, undergoes gamete conjugation, zygote formation, and meiosis within a dominant reef-building coral in situ. On average, sex was detected in 1.5% of the cells analyzed (N = 10,000-40,000 cells observed per sample in a total of 20 samples obtained from 3 Pocillopora colonies). We hypothesize that meiosis follows a two-step process described in other dinoflagellates, in which diploid zygotes form dyads during meiosis I, and triads and tetrads as final products of meiosis II. This study sets the stage for investigating environmental triggers of Symbiodiniaceae sexuality and can accelerate the assisted evolution of a key coral symbiont in order to combat reef degradation.

Monte Carlo study of a convergent X-ray beam for high resolution X-ray fluorescence imaging.

The traditional X-ray tube design is built upon the impact of energetic electrons on high atomic number absorbers producing the X-ray output, consisting of photons due to Bremsstrahlung and fluorescence. Typically, electrons current hits the target within a limited area of a few millimeters square stopping the electrons, which lose their energy and produce the X rays constituting an inherently divergent beam. This geometrical property of traditional X-ray beams is responsible for several undesirable effects when trying to optimize applications requiring high incident fluence spatial concentration, like X-ray fluorescence imaging. This work presents a Monte Carlo study about a novel X-ray tube design, based on a cylindrical target that is capable of producing a convergent X-ray beam aimed at improving overall performance and spatial resolution in certain applications, like X-ray fluorescence imaging. Main design characteristics for relevant parts, like target/anode, filter, and collimator, have been carefully investigated by means of Monte Carlo simulation using two independent codes: FLUKA and PENELOPE. The obtained results suggest the feasibility of the proposed design remarking that high fluence concentration can be achieved, which can be particularly useful for further applications, like tumor targeting by X-ray fluorescence imaging by means of high atomic number nanoparticle infusion, as reported in this work.

Dosimetry of tumor targeting imaging by convergent X-ray beam as compared with nuclear medicine.

During decades nuclear medicine procedures, based on radiolabeled agents, have proved to be efficient for diseases diagnosis and treatment. Radiation emerging from patient is detected aimed at localizing radiotracer distribution that is further correlated with biochemical/metabolic physiological processes. However, a significant drawback associated with current nuclear medicine procedures implementing radionuclide infusion regards to the inherent absorbed dose as well as radiopharmaceuticals' production, storage and elimination from patient body, thus representing a risk at patient and public health level. In the recent years, alternative methods have been proposed to reduce/eliminate radionuclides in some nuclear medicine procedures. The combination of high atomic number nanoparticles infused within patient body with incident X-ray beam, like tumor targeting and treatment, appears as a potential alternative method capable of theranostics. The process is based on inducing X-ray fluorescence and secondary electrons emission in high atomic number nanoparticles by means of excitation with an external X-ray beam, avoiding employing radioactive substances. The present work reports on the dosimetry performance of both methods, comparing whenever the external convergent X-ray beam alternative may involve less or larger radiation dose levels, according to comparable signal/image quality during the procedure. To this aim, a simplified theoretical model is proposed and associated Monte Carlo simulations are performed in order to compare typical case of nuclear medicine imaging with potential performance of an innovative method, called OXIRIS (Orthovoltage X-ray Induced Radiation and Integrated System), based on convergent X-ray beam exciting high atomic number nanoparticles infused in patient. The obtained results support the proposed alternative method's feasibility, once demonstrated that patient absorbed dose levels are relative similar to those currently used by nuclear medicine procedures, whereas dose to targeted region (tumor) are significantly higher, which may be useful for treatment purposes.

Drug use, sexual risk, and structural vulnerability among female sex workers in two urban centers of the Dominican Republic: The EPIC study.

BACKGROUND: Evidence in different countries suggest an association between sex work and drug use. In the Dominican Republic an estimated 60,000-100,000 women work in the sex industry. However, little is known about their drug use behaviors. OBJECTIVE: To characterize the burden of drug use and examine correlates of these behaviors among female sex workers in the Dominican Republic. METHODS: Data for this analysis comes from a cross-sectional study among key populations at risk for HIV. A community sample of female sex workers (N = 389) was recruited using passive and active recruitment strategies. Participants completed a behavioral survey between 2015 and 2016. Logistic regression models were constructed to examine predictors of drug use. RESULTS: Protective factors against marijuana and crack or cocaine use included being heterosexual, having a higher level of education, regular employment, and fewer male sexual partners. Increased odds of crack or cocaine use were associated with incarceration, having slept in a place not meant for human habitation in the last six months, and having ever lived in a batey (a community around a sugar mill where workers and their families live). Participants that used marijuana were generally younger, while those that used crack or cocaine were older. CONCLUSIONS: Our findings highlight characteristics of the social and economic environment that require further research to optimize prevention and care strategies for this population. Public health interventions are needed that address drug use, sexual risk-taking, and helping female sex workers and their families achieve a healthy life.

A high-sensitivity and low dose energy-dispersive X-ray fluorescence system for identification of gadolium accumulations in planar X-ray fluorescence images.

A new technique, based on in-vivo energy dispersive X-ray fluorescence (EDXRF), has been developed to gadolinium (Gd) concentrations identification in planar X-ray fluorescence (XRF) images. Higher signal-to-noise (SNR) ratios while keeping a low radiation dose were achieved. Experimental validation was performed using tissue equivalent phantoms under two different data acquisition criteria. The first criteria consisted on acquiring the energy spectra from different experimental narrow spectrum beam (FWHM = 2.5 keV) with peak central energy above the L edge energy and determining the spectrum which producing Lowest-Limit-of-Detection (Lowest-LoD) for a specific acquisition time. This also provided the minimum dose expected under the condition of minimum irradiation time. The second criteria consisted on measuring the surface dose required to obtain a specific LoD by different narrow spectrum beam, providing the Lowest-Dose setting. Surface (2D) Gd-doped tissue-equivalent phantoms scanning were performed according to optimized scenarios: Lowest-LoD setting (obtaining to central energy of 10.9 keV) and Lowest-Dose setting (obtaining to central energy 12.9 keV). 625 pixel images were acquired in two different conditions: a pre-defined time (5 s) per pixel was set in the first approach, whereas a pre-defined total surface dose (4 mGy) was set to the second approach. According to the results obtained for the first approach, a 58 times reduction was observed when comparing SNR between the Lowest-LoD and Lowest-Dose settings. On the other hand, for the second approach pre-defining total dose during the whole examination, the best SNR was obtained for the Lowest-Dose configuration exhibiting a 42% of increment respecting to the Lowest-LoD configuration and 47 times higher when compared with the limit case of no optimization.

Trajectory control of electron beams using high intensity permanent magnests for linac-adaptable convergent beam radiotherapy.

Convergent beam radiotherapy, or CBRT, currently under development is based on the adaptation of a linear accelerator (linac) to a device which allows to dynamically curve the original trajectory of the electron beam so that it impacts upon a target. This produces a photon beam via Bremsstrahlung which converges on a predetermined focus point (isocenter). Adaptation of the RTHC device is only possible if it is sufficiently compact, as the device must be placed between the linac head exit and the gurney. This requires that new magnetic deflection devices be developed. This paper describes the theoretical and experimental development of controlled-deflection electron beam systems (at energies in MeV ranges) generated in a dual linear accelerator waveguide. A device which follows RTHC geometry is adapted for the system, using new magnetic deflector designs based on permanent neodymium magnets which reach magnetic field intensities in the order of Tesla. The methodology that was developed includes calculations of the radii of curvature with relativistic considerations for mono- and poly-energetic electrons. Deflection angles were calculated based on this theoretical foundation, using a program developed in MatLab® which shows the trajectory of electrons both under ideal conditions (uniform magnetic field) and real conditions (magnetic field defined through intensity distribution). Monte Carlo simulation subroutines were implemented in order to estimate the spectrum of electrons issuing from the linac as well as to directly determine the electron beam trajectory with magnetic deflectors present. Theoretical and simulated results were compared to experiments performed with a clinical linear accelerator, demonstrating correspondence between different methodologies and confirming the ability to achieve electron beam deflection levels necessary for implementation of convergent beam radiotherapy device.

Improvement of appropriate pharmacological prophylaxis in hospitalised cancer patients with a multiscreen e-alert system: a single-centre experience.

PURPOSE: Thromboprophylaxis use among medical inpatients, including cancer patients, is suboptimal. We aimed to evaluate the impact of a novel multiscreen version (v2.0) of an e-alert system for VTE prevention in hospitalised cancer medical patients compared to the original software. METHODS: Prospective study including 989 consecutive adult cancer patients with high-risk of VTE. Patients were followed-up 30 days post-discharge. Two periods were defined, according to the operative software. RESULTS: E-alert v2.0 was associated with an increase in the use of LMWH prophylaxis (65.5% vs. 72.0%); risk difference (95% CI) 0.064 (0.0043-0.12). Only 16% of patients in whom LMWH prophylaxis was not prescribed lacked a contraindication. No significant differences in the rates of VTE (2.9% vs. 3.2%) and major bleeding (2.7% vs. 4.0%) were observed. CONCLUSIONS: E-alert v2.0 further increased the use of appropriate thromboprophylaxis in hospitalised cancer patients, although was not associated with a reduction in VTE incidence.

Enfrentamiento de la ingesta de cuerpo extraño en un Hospital Regional del sur de Chile / Management of foreign body ingestion at a Regional Hospital in southern Chile

Introducción: La ingesta de cuerpos extraños (ICE) es frecuente en pediatría y puede llevar a complicaciones. Nuestro objetivo es revisar la experiencia de nuestro centro en el manejo de estos pacientes y proponer un protocolo de tratamiento. Material y Método: Estudio transversal retrospectivo, observacional y descriptivo, en el cual se revisaron los informes endoscópicos y fichas de pacientes con diagnóstico de ICE manejados por la Unidad de Endoscopia Pediátrica del Hospital Clínico Regional de Concepción entre enero de 2013 y junio de 2017 (53 meses), totalizando 40 casos. El registro y análisis de los datos se realizó con Microsoft® Excel 2016® para MacOS®. Resultados: El promedio de edad fue de 3,96 ± 3,24 años. La moda estadística fue de 2 años. A todos los pacientes se les realizó una endoscopia digestiva alta. El CE más frecuente fue la moneda (61,9%). En 6 casos (14,2%) fue una pila de botón. La retención de CE fue en tercio proximal del esófago (30,9%), el cuerpo gástrico (26,2%) y el tercio distal del esófago (14,2%), extrayéndose principalmente con pinza de cuerpo extraño (90,4%). El 57,5% evidenció alguna lesión relacionada a la ubicación del CE, siendo la más grave la producida por pila de botón. Conclusión: La ICE en niños es una entidad potencialmente peligrosa, por lo que se hace necesario disponer de una unidad de endoscopia pediátrica y protocolos de manejo para evitar complicaciones, sobre todo con objetos de alto riesgo.

Introduction: Foreign body ingestion (FBI) is common in pediatrics and can lead to complications. The aim of the present study is to review the experience of our center in the management of these patients and to propose a treatment protocol. Material and Method: Retrospective, observational and descriptive cross-sectional study, in which the endoscopic reports and records of patients diagnosed with IFB managed by the Pediatric Endoscopy Unit of the Regional Clinical Hospital of Concepción between January 2013 and June 2017 (53 months) were reviewed, with a total of 40 cases. Data recording and analysis was performed with Microsoft® Excel 2016® for MacOS®. Results: The average age was 3,96 ± 3,24 years. The statistical fashion was 2 years. All patients underwent a upper gastrointestinal endoscopy. The most frequent FB was the coin (61,9%). In 6 opportunities (14,2%) was a button batery. FB retention was in the proximal third of the esophagus (30,9%), the gastric body (26,2%) and the distal third of the esophagus (14,2%), being extracted mainly with foreign body clamp (90,4%). The 57,5% showed some injury related to the location of the FB, being the most serious the produced by button batery. Conclusion: FBI in children is a potentially dangerous entity, so it becomes necessary to have a pediatric endoscopy unit and treatment protocols to avoid complications, especially with high-risk objects.

Development of the Nutrition and Functionality Assessment (NFA) among Older Adults in Japan.

OBJECTIVE: Develop and evaluate the feasibility and validity of the Nutrition and Functionality Assessment (NFA) which identifies "target" older adults who could benefit from a personalized program following evaluation of their nutrition status and physical functionality. DESIGN: Cross-sectional study. SETTING: Community and geriatric day-care centers and university in Japan. PARTICIPANTS: 267 older adults aged 65-90. MEASUREMENTS: The "target" individuals were screened based on gait speed (0.6-1.5 m/s). Nutrition (Mini Nutrition Assessment-short form and protein intake), strength (30s chair sit-to-stand and hand-grip strength) and endurance (6-minute walk) were assessed. Physical activity was monitored using a tri-axil accelerometer for a week. Fried frailty phenotype was also assessed. RESULTS: Out of 267 individuals, 185 (69%) had gait speed between 0.6-1.5 m/s, corresponding to our "target" group from which, 184 (95%) completed the nutrition and physical functionality assessments with the physical activity monitoring. The NFA was completed in approximately 30 minutes. No adverse events directly due to the NFA were reported. NFA physical functionality and global scores were significantly related to frailty phenotype but nutrition score was not related to frailty phenotype. CONCLUSION: The study demonstrated that the NFA is a safe and feasible tool to screen target older adults and simultaneously evaluate their nutritional status and physical functionality. Validity of the NFA was partially confirmed by the significant association of the global and physical functionality scores with frailty phenotype. More studies are required to validate and maximize the applicability of the NFA in communities and institutions in Japan and elsewhere.

Feasibility of dose enhancement assessment: Preliminary results by means of Gd-infused polymer gel dosimeter and Monte Carlo study.

This work reports the experimental development of an integral Gd-infused dosimeter suitable for Gd dose enhancement assessment along with Monte Carlo simulations applied to determine the dose enhancement by radioactive and X-ray sources of interest in conventional and electronic brachytherapy. In this context, capability to elaborate a stable and reliable Gd-infused dosimeter was the first goal aimed at direct and accurate measurements of dose enhancement due to Gd presence. Dose-response was characterized for standard and Gd-infused PAGAT polymer gel dosimeters by means of optical transmission/absorbance. The developed Gd-infused PAGAT dosimeters demonstrated to be stable presenting similar dose-response as standard PAGAT within a linear trend up to 13 Gy along with good post-irradiation readout stability verified at 24 and 48 h. Additionally, dose enhancement was evaluated for Gd-infused PAGAT dosimeters by means of Monte Carlo (PENELOPE) simulations considering scenarios for isotopic and X-ray generator sources. The obtained results demonstrated the feasibility of obtaining a maximum enhancement around of (14 ±â€¯1)% for 192Ir source and an average enhancement of (70 ±â€¯13)% for 241Am. However, dose enhancement up to (267 ±â€¯18)% may be achieved if suitable filtering is added to the 241Am source. On the other hand, optimized X-ray spectra may attain dose enhancements up to (253 ±â€¯22) %, which constitutes a promising future alternative for replacing radioactive sources by implementing electronic brachytherapy achieving high dose levels.

Theory, simulation and experiments for precise deflection control of radiotherapy electron beams.

Conventional radiotherapy is mainly applied by linear accelerators. Although linear accelerators provide dual (electron/photon) radiation beam modalities, both of them are intrinsically produced by a megavoltage electron current. Modern radiotherapy treatment techniques are based on suitable devices inserted or attached to conventional linear accelerators. Thus, precise control of delivered beam becomes a main key issue. This work presents an integral description of electron beam deflection control as required for novel radiotherapy technique based on convergent photon beam production. Theoretical and Monte Carlo approaches were initially used for designing and optimizing device´s components. Then, dedicated instrumentation was developed for experimental verification of electron beam deflection due to the designed magnets. Both Monte Carlo simulations and experimental results support the reliability of electrodynamics models used to predict megavoltage electron beam control.

Optimization of the sensitivity/doses relationship for a bench-top EDXRF system used for in vivo quantification of gold nanoparticles.

The present work is devoted to optimizing the sensitivity-doses relationship of a bench-top EDXRF system, with the aim of achieving a detection limit of 0.010mg/ml of gold nanoparticles in tumor tissue (clinical values expected), for doses below 10mGy (value fixed for in vivo application). Tumor phantoms of 0.3cm3 made of a suspension of gold nanoparticles (15nm AurovistTM, Nanoprobes Inc.) were studied at depths of 0-4mm in a tissue equivalent cylindrical phantom. The optimization process was implemented configuring several tube voltages and aluminum filters, to obtain non-symmetrical narrow spectra with fixed FWHM of 5keV and centered among the 11.2-20.3keV. The used statistical figure of merit was the obtained sensitivity (with each spectrum at each depth) weighted by the delivered surface doses. The detection limit of the system was determined measuring several gold nanoparticles concentrations ranging from 0.0010 to 5.0mg/ml and a blank sample into tumor phantoms, considering a statistical fluctuation within 95% of confidence. The results show the possibility of obtaining a detection limit for gold nanoparticles concentrations around 0.010mg/ml for surface tumor phantoms requiring doses around 2mGy.

Thirty years of human infections caused by Yersinia enterocolitica in northern Spain: 1985-2014.

Yersinia enterocolitica infection is a zoonosis with worldwide distribution, gastroenteritis being by far the most common clinical manifestation of human infection. In Gipuzkoa, northern Spain, human Y. enterocolitica infections increased from the mid-1980s to the beginning of the 21st century (from 7·9 to 23·2 annual episodes per 100 000 population) to decrease to 7·2 annual episodes per 100 000 population in the last years of the study. The hospital admission rate due to yersiniosis during the last 15 years of the study was 7·3%. More than 99% of isolates were serotype O:3. Infection affected mainly children under 5 years of age (average rate: 140 episodes per 100 000 population). The incidence in adults was low but hospitalisation increased with age, exceeding 50% in people over 64 years old.

Ensayo estructural no destructivo utilizando microtomografía de rayos X para estimación de diferencias de densidad másica en muestras óseas de conejo / Non-destructive structural assay using X-ray micro-tomography to estimate mass density differences in rabbit bone samples

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.

Dosimetric and bremsstrahlung performance of a single convergent beam for teletherapy device.

The present work investigates preliminary feasibility and characteristics of a new type of radiation therapy modality based on a single convergent beam of photons. The proposal consists of the design of a device capable of generating convergent X-ray beams useful for radiotherapy. The main goal is to achieve high concentrated dose delivery. The first step is an analytical approach in order to characterize the dosimetric performance of the hypothetical convergent photon beam. Then, the validated FLUKA Monte Carlo main code is used to perform complete radiation transport to account also for scattering effects. The proposed method for producing convergent X-rays is mainly based on the bremsstrahlung effect. Hence the operating principle of the proposed device is described in terms of bremsstrahlung production. The work is mainly devoted characterizing the effect on the bremsstrahlung yield due to accessories present in the device, like anode material and geometry, filtration and collimation systems among others. The results obtained for in-depth dose distributions, by means of analytical and stochastic approaches, confirm the presence of a high dose concentration around the irradiated target, as expected. Moreover, it is shown how this spot of high dose concentration depends upon the relevant physical properties of the produced convergent photon beam. In summary, the proposed design for producing single convergent X-rays attained satisfactory performance for achieving high dose concentration around small targets depending on beam spot size that may be used for some applications in radiotherapy, like radiosurgery.