Development and Implementation of the Use of Optically Stimulated Luminescent Detectors in the Radiological Physics Center Anthropomorphic Quality Assurance Phantoms

The Radiological Physics Center (RPC) uses both on-site and remote reviews to credential institutions for participation in clinical trials. Anthropomorphic quality assurance (QA) phantoms are one tool the RPC uses to remotely audit institutions, which include thermoluminescent dosimeters (TLDs) and radiochromic film. The RPC desires to switch from TLD as the absolute dosimeter in the phantoms, to optically stimulated luminescent dosimeters (OSLDs), but a problem lies in the angular dependence exhibited by the OSLD. The purpose of this study was to characterize the angular dependence of OSLD and establish a correction factor if necessary, to provide accurate dosimetric measurements as a replacement for TLD in the QA phantoms. A 10 cm diameter high-impact polystyrene spherical phantom was designed and constructed to hold an OSLD to study the angular response of the dosimeter under the simplest of circumstances for both coplanar and non-coplanar treatment deliveries. OSLD were irradiated in the spherical phantom, and the responses of the dosimeter from edge-on angles were normalized to the response when irradiated with the beam incident normally on the surface of the dosimeter. The average normalized response was used to establish an angular correction factor for 6 MV and 18 coplanar treatments, and for 6 MV non-coplanar treatments specific to CyberKnife. The RPC pelvic phantom dosimetry insert was modified to hold OSLD, in addition to the TLD, adjacent to the planes of film. Treatment plans of increasing angular beam delivery were developed, three in Pinnacle v9.0 (4-field box, IMRT, and VMAT) and one in Accuray’s MultiPlan v3.5.3 (CyberKnife). The plans were delivered to the pelvic phantom containing both TLD and OSLD in the target volume. The pelvic phantom was also sent to two institutions to be irradiated as trials, one delivering IMRT, and the other a CyberKnife treatment. For the IMRT deliveries and the two institution trials, the phantom also included film in the sagittal and coronal planes. The doses measured from the TLD and OSLD were calculated for each irradiation, and the angular correction factors established from the spherical phantom irradiations were applied to the OSLD dose. The ratio of the TLD dose to the angular corrected OSLD dose was calculated for each irradiation. The corrected OSLD dose was found to be within 1% of the TLD measured dose for all irradiations, with the exception of the in-house CyberKnife deliveries. The films were normalized to both TLD measured dose and the corrected OSLD dose. Dose profiles were obtained and gamma analysis was performed using a 7%/4 mm criteria, to compare the ability of the OSLD, when corrected for the angular dependence, to provide equivalent results to TLD. The results of this study indicate that the OSLD can effectively be used as a replacement for TLD in the RPC’s anthropomorphic QA phantoms for coplanar treatment deliveries when a correction is applied for the dosimeter’s angular dependence.

Improved Techniques for Acquisition and Analysis of Dynamic Contrast-Enhanced Magnetic Resonance Imaging for Detecting Vascular Permeability in the Central Nervous System

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a noninvasive technique for quantitative assessment of the integrity of blood-brain barrier and blood-spinal cord barrier (BSCB) in the presence of central nervous system pathologies. However, the results of DCE-MRI show substantial variability. The high variability can be caused by a number of factors including inaccurate T1 estimation, insufficient temporal resolution and poor contrast-to-noise ratio. My thesis work is to develop improved methods to reduce the variability of DCE-MRI results. To obtain fast and accurate T1 map, the Look-Locker acquisition technique was implemented with a novel and truly centric k-space segmentation scheme. In addition, an original multi-step curve fitting procedure was developed to increase the accuracy of T1 estimation. A view sharing acquisition method was implemented to increase temporal resolution, and a novel normalization method was introduced to reduce image artifacts. Finally, a new clustering algorithm was developed to reduce apparent noise in the DCE-MRI data. The performance of these proposed methods was verified by simulations and phantom studies. As part of this work, the proposed techniques were applied to an in vivo DCE-MRI study of experimental spinal cord injury (SCI). These methods have shown robust results and allow quantitative assessment of regions with very low vascular permeability. In conclusion, applications of the improved DCE-MRI acquisition and analysis methods developed in this thesis work can improve the accuracy of the DCE-MRI results.

AN EVALUATION OF THE CONSISTENCY OF IMRT PATIENT-SPECIFIC QA TECHNIQUES

To ensure the integrity of an intensity modulated radiation therapy (IMRT) treatment, each plan must be validated through a measurement-based quality assurance (QA) procedure, known as patient specific IMRT QA. Many methods of measurement and analysis have evolved for this QA. There is not a standard among clinical institutions, and many devices and action levels are used. Since the acceptance criteria determines if the dosimetric tools’ output passes the patient plan, it is important to see how these parameters influence the performance of the QA device. While analyzing the results of IMRT QA, it is important to understand the variability in the measurements. Due to the different form factors of the many QA methods, this reproducibility can be device dependent. These questions of patient-specific IMRT QA reproducibility and performance were investigated across five dosimeter systems: a helical diode array, radiographic film, ion chamber, diode array (AP field-by-field, AP composite, and rotational composite), and an in-house designed multiple ion chamber phantom. The reproducibility was gauged for each device by comparing the coefficients of variation (CV) across six patient plans. The performance of each device was determined by comparing each one’s ability to accurately label a plan as acceptable or unacceptable compared to a gold standard. All methods demonstrated a CV of less than 4%. Film proved to have the highest variability in QA measurement, likely due to the high level of user involvement in the readout and analysis. This is further shown by how the setup contributed more variation than the readout and analysis for all of the methods, except film. When evaluated for ability to correctly label acceptable and unacceptable plans, two distinct performance groups emerged with the helical diode array, AP composite diode array, film, and ion chamber in the better group; and the rotational composite and AP field-by-field diode array in the poorer group. Additionally, optimal threshold cutoffs were determined for each of the dosimetry systems. These findings, combined with practical considerations for factors such as labor and cost, can aid a clinic in its choice of an effective and safe patient-specific IMRT QA implementation.

Scanned Ion Beam Therapy for Thoracic Tumors

Although frequently cured of Hodgkin lymphoma, adolescents and young adults can develop radiation induced second cancers. These patients could potentially benefit from scanned ion radiotherapy yet likely would require motion mitigation strategies. In theory, four-dimensional (4D) optimization of ion beam fields for individual motion states of respiration can enable superior sparing of healthy tissue near moving targets, compared to other motion mitigation strategies. Furthermore, carbon-ion therapy can sometimes provide greater relative biological effectiveness (RBE) for cell sterilization in a target but nearly equivalent RBE in tissue upstream of the target, compared to proton therapy. Thus, we expected that for some patients with Hodgkin lymphoma, carbon-ion therapy would reduce the predicted risk of second cancer incidence in the breast compared with proton therapy. The purpose of this work was to determine whether 4D-optimized carbon-ion therapy would significantly reduce the predicted risk of radiation induced second cancers in the breast for female Hodgkin lymphoma patients while preserving tumor control compared with proton therapy. To achieve our goals, we first investigated whether 4D-optimized carbon beam tracking could reduce dose to volumes outside a moving target compared with 3D-optimized carbon beam tracking while preserving target dose coverage. To understand the reliability of scanned carbon beam tracking, we studied the robustness of dose distributions in thoracic targets to uncertainties in patient motion. Finally, we investigated whether using carbon-ion therapy instead of proton therapy would significantly reduce the predicted risk of second cancer in the breast for a sample of Hodgkin lymphoma patients. We found that 4D-optimized ion beam tracking therapy can reduce the maximum dose to critical structures near a moving target by as much as 53%, compared to 3D-optimized ion beam tracking therapy. We validated these findings experimentally using a scanned carbon ion synchrotron and a motion phantom. We found scanned carbon beam tracking to be sensitive to a number of motion uncertainties, most notably phase delays in tracking, systematic spatial errors, and interfractional motion changes. Our findings indicate that a lower risk of second cancer in the breast might be expected for some Hodgkin lymphoma patients using carbon-ion therapy instead of proton therapy. For our reference scenario, we found the ratio of risk to be 0.77 ± 0.35 for radiogenic breast cancer after carbon-ion therapy versus proton therapy. Our findings were dependent on the RBE values for tumor induction and the radiosensitivity of breast tissue, as well as the physical dose distribution.

A dual resonance, image -guided, volume localization technique for magnetic resonance spectroscopy

An interleaved, dual resonance, volume localization technique for $\sp1$H/$\sp{31}$P magnetic resonance spectroscopy has been designed, implemented on a 2 T imager/spectrometer, and verified with phantom studies.^ Localization techniques, including several single voxel techniques and spectroscopic imaging, were implemented, and studies were performed to compare the efficiency of each sequence of $\sp1$H/$\sp{31}$P spectral acquisitions. The sequence chosen was a hybrid of the stimulated echo single voxel technique and the spectroscopic imaging technique.^ Water suppression during the $\sp1$H spectral acquisitions was accomplished by the use of three narrow bandwidth RF saturation pulses in combination with three spoiler gradients. The spoiler gradient amplitudes were selected on the basis of a numerical solution of the Bloch equations. A post-acquisition water suppression algorithm was used to minimize any residual water signal.^ For interleaved $\sp1$H/$\sp{31}$P acquisitions, a dual resonance RF coil was constructed and interfaced to the existing RF detection system via a custom-designed dual resonance transcoupler and switching system. Programmable attenuators were incorporated to allow for changes in receiver and transmitter attenuation "on the fly".^ To provide the rapidly switched gradient fields required for the $\sp1$H/$\sp{31}$P acquisitions, an actively screened gradient coil system was designed and implemented. With this system, gradient field rise times on the order of 100 $\mu$s were obtained. These rapid switching times were necessary for minimizing intrasequence delays and for improving localization quality and water suppression efficiency.^ The interleaved $\sp1$H/$\sp{31}$P volume localization technique was tested using a two-compartment phantom. Analysis of the data showed that the spectral contamination was less than three percent. One-to-one spatial correspondence of the $\sp1$H and $\sp{31}$P spectra was verified and allowed for direct correlation of the spectral data with a standard magnetic resonance image. ^

Development of a SPECT -based three-dimensional treatment planner for radionuclide therapy with iodine -131

Accurate calculation of absorbed dose to target tumors and normal tissues in the body is an important requirement for establishing fundamental dose-response relationships for radioimmunotherapy. Two major obstacles have been the difficulty in obtaining an accurate patient-specific 3-D activity map in-vivo and calculating the resulting absorbed dose. This study investigated a methodology for 3-D internal dosimetry, which integrates the 3-D biodistribution of the radionuclide acquired from SPECT with a dose-point kernel convolution technique to provide the 3-D distribution of absorbed dose. Accurate SPECT images were reconstructed with appropriate methods for noise filtering, attenuation correction, and Compton scatter correction. The SPECT images were converted into activity maps using a calibration phantom. The activity map was convolved with an $\sp{131}$I dose-point kernel using a 3-D fast Fourier transform to yield a 3-D distribution of absorbed dose. The 3-D absorbed dose map was then processed to provide the absorbed dose distribution in regions of interest. This methodology can provide heterogeneous distributions of absorbed dose in volumes of any size and shape with nonuniform distributions of activity. Comparison of the activities quantitated by our SPECT methodology to true activities in an Alderson abdominal phantom (with spleen, liver, and spherical tumor) yielded errors of $-$16.3% to 4.4%. Volume quantitation errors ranged from $-$4.0 to 5.9% for volumes greater than 88 ml. The percentage differences of the average absorbed dose rates calculated by this methodology and the MIRD S-values were 9.1% for liver, 13.7% for spleen, and 0.9% for the tumor. Good agreement (percent differences were less than 8%) was found between the absorbed dose due to penetrating radiation calculated from this methodology and TLD measurement. More accurate estimates of the 3-D distribution of absorbed dose can be used as a guide in specifying the minimum activity to be administered to patients to deliver a prescribed absorbed dose to tumor without exceeding the toxicity limits of normal tissues. ^

Odontodisplasia regional : caso clínico

La odontodisplasia regional, también denominada diente fantasma o detención localizada del desarrollo dental, es una anomalía estructural del desarrollo, compleja y rara. Su etiología es desconocida y no presenta un patrón hereditario, aunque se han considerado factores locales como alteraciones vasculares y traumatismos locales. Puede afectar ambas denticiones: temporal y permanente; existe una anormal aposición dentinaria, que a su vez está detenida precozmente. Se encuentran afectados todos los componentes histológicos del órgano dentario y radiográficamente el aspecto fantasma es típico: raíces cortas, coronas que semejan cáscaras y aspecto dismórfico general. Se recibieron estudios radiográficos correspondientes a una niña de 10 años derivada del Hospital Materno Infantil de la ciudad de Azul, provincia de Buenos Aires. Luego del análisis de signos radiográficos se determina el diagnóstico de odontodisplasia regional en los cuadrantes superior e inferior izquierdos. Se sugiere la investigación de antecedentes traumáticos al presentarse la lesión en dos cuadrantes isolaterales.

Situación del mercado laboral de dos localidades de la provincia de San Luis en la zona de influencia de la agriculturización

El fenómeno de agriculturización que ha tenido lugar en nuestro país durante los últimos años no ha impactado solamente en la región de la República Argentina tradicionalmente agrícola. También lo ha hecho, aunque de una manera diferente, en la Provincia de San Luis. En esta provincia, dicho fenómeno convive con otras particularidades, como es la radicación industrial promocionada, que marcó profundamente el aparato productivo provincial o, más recientemente, una política pública de amplio espectro como el Plan de Inclusión Social, que modificó drásticamente los indicadores del mercado laboral sanluiseño. Este trabajo tiene por objeto estudiar la situación laboral de dos localidades de la Provincia de San Luis emplazadas en zonas de importante producción agrícola, considerando la influencia de las políticas públicas locales y del sector industrial que aún mantiene una importante cuota del Producto Bruto Geográfico. Para esto se realiza un análisis comparativo entre ellas y con la situación provincial, caracterizada por el Aglomerado San Luis y El Chorrillo, que releva la Encuesta Permanente de Hogares del indec. La información utilizada proviene de datos secundarios procedentes de organismos nacionales y de relevamientos propios realizados en las localidades estudiadas

Abigeato y administración de justicia en la campaña bonaerense durante la segunda mitad siglo XIX

La práctica del abigeato así como otros usos que atentaban contra la propiedad semoviente fue condenada de manera cada vez más vehemente a lo largo del siglo XIX. Este rechazo se plasmó en la legislación, que de manera continua, elaboraron las autoridades procurando limitarlas. El estudio de un conjunto de procesos criminales y sumarios permite indagar en las prácticas vigentes en torno al ganado así como la visión de los magistrados. Dichos usos no fueron una prerrogativa exclusiva de los sujetos señalados como "vagos y malentretenidos". El espectro social que se sirvió de la apropiación ilegal de animales era muy amplio e incluyó a personas con apellidos que remitían a las familias más poderosas de la campaña. Por otro lado, el abigeato así como otros delitos asociados a éste muestran las dificultades en torno a la implantación de un determinado orden social en la campaña bonaerense, donde el respeto a la propiedad privada era uno de sus pilares fundamentales.

Situación del mercado laboral de dos localidades de la provincia de San Luis en la zona de influencia de la agriculturización

El fenómeno de agriculturización que ha tenido lugar en nuestro país durante los últimos años no ha impactado solamente en la región de la República Argentina tradicionalmente agrícola. También lo ha hecho, aunque de una manera diferente, en la Provincia de San Luis. En esta provincia, dicho fenómeno convive con otras particularidades, como es la radicación industrial promocionada, que marcó profundamente el aparato productivo provincial o, más recientemente, una política pública de amplio espectro como el Plan de Inclusión Social, que modificó drásticamente los indicadores del mercado laboral sanluiseño. Este trabajo tiene por objeto estudiar la situación laboral de dos localidades de la Provincia de San Luis emplazadas en zonas de importante producción agrícola, considerando la influencia de las políticas públicas locales y del sector industrial que aún mantiene una importante cuota del Producto Bruto Geográfico. Para esto se realiza un análisis comparativo entre ellas y con la situación provincial, caracterizada por el Aglomerado San Luis y El Chorrillo, que releva la Encuesta Permanente de Hogares del indec. La información utilizada proviene de datos secundarios procedentes de organismos nacionales y de relevamientos propios realizados en las localidades estudiadas

Abigeato y administración de justicia en la campaña bonaerense durante la segunda mitad siglo XIX

La práctica del abigeato así como otros usos que atentaban contra la propiedad semoviente fue condenada de manera cada vez más vehemente a lo largo del siglo XIX. Este rechazo se plasmó en la legislación, que de manera continua, elaboraron las autoridades procurando limitarlas. El estudio de un conjunto de procesos criminales y sumarios permite indagar en las prácticas vigentes en torno al ganado así como la visión de los magistrados. Dichos usos no fueron una prerrogativa exclusiva de los sujetos señalados como "vagos y malentretenidos". El espectro social que se sirvió de la apropiación ilegal de animales era muy amplio e incluyó a personas con apellidos que remitían a las familias más poderosas de la campaña. Por otro lado, el abigeato así como otros delitos asociados a éste muestran las dificultades en torno a la implantación de un determinado orden social en la campaña bonaerense, donde el respeto a la propiedad privada era uno de sus pilares fundamentales.

Situación del mercado laboral de dos localidades de la provincia de San Luis en la zona de influencia de la agriculturización

El fenómeno de agriculturización que ha tenido lugar en nuestro país durante los últimos años no ha impactado solamente en la región de la República Argentina tradicionalmente agrícola. También lo ha hecho, aunque de una manera diferente, en la Provincia de San Luis. En esta provincia, dicho fenómeno convive con otras particularidades, como es la radicación industrial promocionada, que marcó profundamente el aparato productivo provincial o, más recientemente, una política pública de amplio espectro como el Plan de Inclusión Social, que modificó drásticamente los indicadores del mercado laboral sanluiseño. Este trabajo tiene por objeto estudiar la situación laboral de dos localidades de la Provincia de San Luis emplazadas en zonas de importante producción agrícola, considerando la influencia de las políticas públicas locales y del sector industrial que aún mantiene una importante cuota del Producto Bruto Geográfico. Para esto se realiza un análisis comparativo entre ellas y con la situación provincial, caracterizada por el Aglomerado San Luis y El Chorrillo, que releva la Encuesta Permanente de Hogares del indec. La información utilizada proviene de datos secundarios procedentes de organismos nacionales y de relevamientos propios realizados en las localidades estudiadas

Abigeato y administración de justicia en la campaña bonaerense durante la segunda mitad siglo XIX

La práctica del abigeato así como otros usos que atentaban contra la propiedad semoviente fue condenada de manera cada vez más vehemente a lo largo del siglo XIX. Este rechazo se plasmó en la legislación, que de manera continua, elaboraron las autoridades procurando limitarlas. El estudio de un conjunto de procesos criminales y sumarios permite indagar en las prácticas vigentes en torno al ganado así como la visión de los magistrados. Dichos usos no fueron una prerrogativa exclusiva de los sujetos señalados como "vagos y malentretenidos". El espectro social que se sirvió de la apropiación ilegal de animales era muy amplio e incluyó a personas con apellidos que remitían a las familias más poderosas de la campaña. Por otro lado, el abigeato así como otros delitos asociados a éste muestran las dificultades en torno a la implantación de un determinado orden social en la campaña bonaerense, donde el respeto a la propiedad privada era uno de sus pilares fundamentales.