Verification of intensity modulated stereotactic radiotherapy using Monte Carlo calculations and EPID dosimetry

The purpose of this work was to develop a comprehensive IMSRT QA procedure that examined, using EPID dosimetry and Monte Carlo (MC) calculations, each step in the treatment planning and delivery process. These steps included verification of the field shaping, treatment planning system (RTPS) dose calculations, and patient dose delivery. Verification of each step in the treatment process is assumed to result in correct dose delivery to the patient. ^ The accelerator MC model was verified against commissioning data for field sizes from 0.8 × 0.8 cm 2 to 10 × 10 cm 2. Depth doses were within 2% local percent difference (LPD) in low gradient regions and 1 mm distance to agreement (DTA) in high gradient regions. Lateral profiles were within 2% LPD in low gradient regions and 1 mm DTA in high gradient regions. Calculated output factors were within 1% of measurement for field sizes ≥1 × 1 cm2. ^ The measured and calculated pretreatment EPID dose patterns were compared using criteria of 5% LPD, 1 mm DTA, or 2% of central axis pixel value with ≥95% of compared points required to pass for successful verification. Pretreatment field verification resulted in 97% percent of the points passing. ^ The RTPS and Monte Carlo phantom dose calculations were compared using 5% LPD, 2 mm DTA, or 2% of the maximum dose with ≥95% of compared points required passing for successful verification. RTPS calculation verification resulted in 97% percent of the points passing. ^ The measured and calculated EPID exit dose patterns were compared using criteria of 5% LPD, 1 mm DTA, or 2% of central axis pixel value with ≥95% of compared points required to pass for successful verification. Exit dose verification resulted in 97% percent of the points passing. ^ Each of the processes above verified an individual step in the treatment planning and delivery process. The combination of these verification steps ensures accurate treatment delivery to the patient. This work shows that Monte Carlo calculations and EPID dosimetry can be used to quantitatively verify IMSRT treatments resulting in improved patient care and, potentially, improved clinical outcome. ^

DEVELOPMENT AND IMPLEMENTATION OF A REMOTE AUDIT TOOL FOR HIGH DOSE RATE (HDR) 192IR BRACHYTHERAPY USING OPTICALLY STIMULATED LUMINESCENCE DOSIMETRY

This work aimed to create a mailable and OSLD-based phantom with accuracy suitable for RPC audits of HDR brachytherapy sources at institutions participating in NCI-funded cooperative clinical trials. An 8 × 8 × 10 cm3 prototype with two slots capable of holding nanoDot Al2O3:C OSL dosimeters (Landauer, Glenwood, IL) was designed and built. The phantom has a single channel capable of accepting all 192Ir HDR brachytherapy sources in current clinical use in the United States. Irradiations were performed with an 192Ir HDR source to determine correction factors for linearity with dose, dose rate, and the combined effect of irradiation energy and phantom construction. The uncertainties introduced by source positioning in the phantom and timer resolution limitations were also investigated. It was found that the linearity correction factor was where dose is in cGy, which differed from that determined by the RPC for the same batch of dosimeters under 60Co irradiation. There was no significant dose rate effect. Separate energy+block correction factors were determined for both models of 192Ir sources currently in clinical use and these vendor-specific correction factors differed by almost 2.6%. For Nucletron sources, this correction factor was 1.026±0.004 (99% Confidence Interval) and for Varian sources it was 1.000±0.007 (99% CI). Reasonable deviations in source positioning within the phantom and the limited resolution of the source timer had insignificant effects on the ability to measure dose. Overall measurement uncertainty of the system was estimated to be ±2.5% for both Nucletron and Varian source audits (95% CI). This uncertainty was sufficient to establish a ±5% acceptance criterion for source strength audits under a formal RPC audit program. Trial audits of eight participating institutions resulted in an average RPC-to-institution dose ratio of 1.000 with a standard deviation of 0.011.

Understanding the Influence of Photon Energy on 6MV Non Reference Dosimetry and CT Dosimetry using TLD and OSLD

Measurement of the absorbed dose from ionizing radiation in medical applications is an essential component to providing safe and reproducible patient care. There are a wide variety of tools available for measuring radiation dose; this work focuses on the characterization of two common, solid-state dosimeters in medical applications: thermoluminescent dosimeters (TLD) and optically stimulated luminescent dosimeters (OSLD). There were two main objectives to this work. The first objective was to evaluate the energy dependence of TLD and OSLD for non-reference measurement conditions in a radiotherapy environment. The second objective was to fully characterize the OSLD nanoDot in a CT environment, and to provide validated calibration procedures for CT dose measurement using OSLD. Current protocols for dose measurement using TLD and OSLD generally assume a constant photon energy spectrum within a nominal beam energy regardless of measurement location, tissue composition, or changes in beam parameters. Variations in the energy spectrum of therapeutic photon beams may impact the response of TLD and OSLD and could thereby result in an incorrect measure of dose unless these differences are accounted for. In this work, we used a Monte Carlo based model to simulate variations in the photon energy spectra of a Varian 6MV beam; then evaluated the impact of the perturbations in energy spectra on the response of both TLD and OSLD using Burlin Cavity Theory. Energy response correction factors were determined for a range of conditions and compared to measured correction factors with good agreement. When using OSLD for dose measurement in a diagnostic imaging environment, photon energy spectra are often referenced to a therapy-energy or orthovoltage photon beam – commonly 250kVp, Co-60, or even 6MV, where the spectra are substantially different. Appropriate calibration techniques specifically for the OSLD nanoDot in a CT environment have not been presented in the literature; furthermore the dependence of the energy response of the calibration energy has not been emphasized. The results of this work include detailed calibration procedures for CT dosimetry using OSLD, and a full characterization of this dosimetry system in a low-dose, low-energy setting.

Evaluation of PRESAGE® dosimeters for brachytherapy sources and the 3D dosimetry and characterization of the new AgX100 125I seed model

With continuous new improvements in brachytherapy source designs and techniques, method of 3D dosimetry for treatment dose verifications would better ensure accurate patient radiotherapy treatment. This study was aimed to first evaluate the 3D dose distributions of the low-dose rate (LDR) Amersham 6711 OncoseedTM using PRESAGE® dosimeters to establish PRESAGE® as a suitable brachytherapy dosimeter. The new AgX100 125I seed model (Theragenics Corporation) was then characterized using PRESAGE® following the TG-43 protocol. PRESAGE® dosimeters are solid, polyurethane-based, 3D dosimeters doped with radiochromic leuco dyes that produce a linear optical density response to radiation dose. For this project, the radiochromic response in PRESAGE® was captured using optical-CT scanning (632 nm) and the final 3D dose matrix was reconstructed using the MATLAB software. An Amersham 6711 seed with an air-kerma strength of approximately 9 U was used to irradiate two dosimeters to 2 Gy and 11 Gy at 1 cm to evaluate dose rates in the r=1 cm to r=5 cm region. The dosimetry parameters were compared to the values published in the updated AAPM Report No. 51 (TG-43U1). An AgX100 seed with an air-kerma strength of about 6 U was used to irradiate two dosimeters to 3.6 Gy and 12.5 Gy at 1 cm. The dosimetry parameters for the AgX100 were compared to the values measured from previous Monte-Carlo and experimental studies. In general, the measured dose rate constant, anisotropy function, and radial dose function for the Amersham 6711 showed agreements better than 5% compared to consensus values in the r=1 to r=3 cm region. The dose rates and radial dose functions measured for the AgX100 agreed with the MCNPX and TLD-measured values within 3% in the r=1 to r=3 cm region. The measured anisotropy function in PRESAGE® showed relative differences of up to 9% with the MCNPX calculated values. It was determined that post-irradiation optical density change over several days was non-linear in different dose regions, and therefore the dose values in the r=4 to r=5 cm regions had higher uncertainty due to this effect. This study demonstrated that within the radial distance of 3 cm, brachytherapy dosimetry in PRESAGE® can be accurate within 5% as long as irradiation times are within 48 hours.

La dignidad en la diversidad : educación especial — terapia ocupacional

Es la intención de este trabajo aportar reflexiones y poner en perspectiva la complejidad de avanzar en una Educación para la Diversidad que haga posible la inclusión y con ello el derecho universal a la Educación como bien social. En este momento histórico las diversidades han tomado voz y forma, al cuestionar nuestro modo de pensar la vida social. Las culturas, los sujetos, los géneros, los lenguajes, los imaginarios y las formas de habitar un mundo diverso, encuen tran eco en la sociedad de la información, en apariencia un mundo sin fronteras. Frente a las transformaciones tecnológicas y económicas del siglo XXI cabe preguntarse cuál es nuestra sensibilidad ante la diferencia, cuanto hemos avanzado en la capacidad para reconocer a “los Otros", que sabemos de sus sueños y frustraciones, como nos estamos preparando para convivir “ Nosotros y los Otros", en un mundo polifónico. Frente a estas problemáticas el aporte interdisciplinario permitirá buscar modelos alternativos que rompan este círculo a través de dispositivos de inclusión social reduciendo los temores y mitos que han impulsado en otras ocasiones a marginar a las personas. El contenido interdisciplinar de la Educación Especial ha permitido y requiere la convergencia de disciplinas, entre ellas la Terapia Ocupacional.

Riesgos ergonómicos; conocimiento y aplicación de los principios de mecánica corporal en los servicios de maternidad y terapia intensiva

Debido al índice de enfermedades ocupacionales y accidentes de trabajos observados y registrados en el Hospital Enfermeros Argentinos de General Alvear, se puede inferir que el personal de enfermería posee escaso conocimiento teórico y práctico sobre los factores de riesgo que deben tenerse en cuenta al momento de prevenir accidentes laborales causados por las incorrectas posturas corporales y el uso inadecuado de la fuerza al trabajar con pacientes que necesitan ser trasladados de un lugar a otro. Es por ello que el personal de enfermería debe poseer una habilidad técnica que permita aplicarlo en el área que se representa, tanto como para el paciente, como para beneficio personal. Lo ideal es que se conozcan los factores de riesgo y que se puedan prevenir los accidentes de trabajo.

La salud pública en terapia intensiva. Reflexiones sobre los repertorios de acción colectiva de los trabajadores/as del Hospital Castro Rendón (Neuquén Capital)

Fil: Beliera, Anabel. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

La salud pública en terapia intensiva : Reflexiones sobre los repertorios de acción colectiva de los trabajadores/as del Hospital Castro Rendón [Neuquén Capital]

El régimen neoliberal de acumulación y de reproducción de las clases fundamentales dejó afuera de los privilegios a más de la mitad de la población. Sus desgarradoras consecuencias no demoraron en hacerse visibles en nuestro continente y se desarrollaron fuertes procesos de lucha contra el mismo. En nuestro país fueron numerosas las investigaciones orientadas a comprender las continuidades y rupturas en las prácticas políticas de las clases subalternas frente a los cambios estructurales, sin embargo la mayoría centró su mirada en la provincia de Buenos Aires, contándose con escasa bibliografía respecto a otras provincias argentinas. Consideramos que Neuquén es un espacio social que presenta particularidades interesantes para pensar este problema. En este trabajo analizaremos las acciones colectivas de los trabajadores del Hospital Castro Rendón [HCR] de Neuquén Capital, recuperando los sentidos que los actores les adjudican a sus prácticas militantes y a sus formas de organización. A partir de observaciones participantes y entrevistas semi-estructuradas en profundidad realizadas a los/as trabajadores/as del HCR, se analizaron la estructura de oportunidades políticas, los procesos de enmarcación y la conformación de estructuras de movilización que están implicadas en sus acciones colectivas, para poder dar cuenta de las continuidades y rupturas en las protestas de los trabajadores del hospital de mayor complejidad de la provincia

Reflexiones metodológicas sobre algunas contribuciones de la terapia familiar sistémica a un estudio antropológico de la familia

El fenómeno migratorio ha sido tratado a partir de diferentes estudios históricos, sociológicos, demográficos y antropológicos. Muchas veces estos abordajes solo ofrecen respuestas parciales a las problemáticas que conforman la migración. Nuestras investigaciones se centraron en el estudio de grupos de inmigrantes caboverdeanos en Argentina, aportando modelos sobre la organización e interacción de esos grupos, con el fin de explorar temas críticos, como inmigración y familia, identidad y etnicidad, entre otros. Luego de años de trabajo hemos ajustado metodologías, sobre todo las derivadas de la antropología tradicional, buscando alternativas, "reciclando" premisas, pautas y técnicas de otras disciplinas como la psicología (en particular la terapia familiar de orientación sistémica). En este trabajo reflexionamos sobre algunas cuestiones metodológicas, particularmente el uso de genogramas puestos en práctica en el estudio del parentesco y de la familia caboverdeana en un contexto migratorio, cuyo análisis fue uno de los objetivos planteados en el proyecto de investigación sobre el mencionado grupo en la Argentina

El recurso auto-epistolar como terapia : Motivos temáticos recurrentes y greguerías en Cartas a mí mismo (1956) de Ramón Gómez de la Serna

Ramón Gómez de la Serna escribió a finales de los años 40 y principios de los 50 las Cartas a mí mismo, publicadas en conjunto en 1956. La escritura de dichas cartas le sirve al autor de terapia narrativa. Analizaré cómo se muestra su obsesión por la muerte, los testimonios contradictorios de la soledad experimentada en América y diversas alusiones que reflejan felicidad e infelicidad en una escritura literaria que oscila entre la tristeza y lo lúdico, en la cual abundan las greguerías