Monte Carlo simulation of large angle scattering effects in heavy ion elastic recoil detection analysis and ion transmission through nanoapertures

Heavy Ion Elastic Recoil Detection Analysis (HIERDA) is a versatile Ion Beam Analysis technique well suited to multi-elemental depth profiling of thin layered structures and near-surface regions of materials. An existing limitation is the inability to accurately account for the pronounced broadening and tailing effects of multiple scattering typically seen in HIERDA spectra. This thesis investigates the role of multiple large angle scattering in heavy ion applications such as HIERDA, and seeks to quantify its contribution to experimental output. This is achieved primarily by the development of a computer simulation capable of predicting these contributions and using it to classify and quantify the interactions that cause them. Monte Carlo ion transport simulation is used to generate simulated HIERDA spectra and the results are compared to experimental data acquired using the Time of Flight HIERDA facility at the Australian Nuclear Science and Technology Organisation. A Monte Carlo simulation code was adapted to the simulation of HIERDA spectra with considerable attention on improving the modelling efficiency to reduce processing time. Efficiency enhancements have achieved simulation time reductions of two to three orders of magnitude. The simulation is shown to satisfactorily reproduce the complex shape of HIERDA spectra. Some limitations are identified in the ability to accurately predict peak widths and the absolute magnitude of low energy tailing in some cases. The code is used to identify the plural scattering contribution to the spectral features under investigation, and the complexity of plurally scattered ion and recoil paths is demonstrated. The program is also shown to be useful in the interpretation of overlapped energy spectra of elements of similar mass whose signals cannot be reliably separated experimentally. The effect of large angle scattering on the transmission of heavy ions through a nano-scale aperture mask, used to collimate an ion beam to a very small beam spot, is modelled using a version of the program adapted to handle the more complex geometry of the aperture mask. The effectiveness of nano-aperture collimation was studied for a variety of ion-energy combinations. Intensity, energy, and angular distributions of transmitted ions were calculated to quantify the degree to which scattering within the mask limits the spatial resolution achievable. The simulation successfully predicted the effect of misaligning the aperture and the beam, and the result has subsequently been observed experimentally. Transmitted ion distributions showed that the higher energy heavier ions studied are more effectively collimated than are lower energy lighter ions. However, there is still a significant probability of transmission of heavy ions with substantial residual energy beyond the perimeter of the aperture. For the intended application, ion beam lithography, these ions are likely to be problematic. The results indicate that medium energy He ions are the more attractive option, as the residual energy of scattered transmitted ions can be more readily managed by customising the etching process. Continuing research by experimentalists working in this area is proceeding in this direction as a result of the conclusions from this work

Modification of kraft wood-pulp fibre with silica for surface functionalisation

A new science strategy for natural fibre modification was devised in which glass surface properties would be imparted to wood-derived fibre. The enhancements known from addition of silane reagents to glass fibre–polymer composites could therefore be realised for modified cellulose fibre–polymer composites. A process is described whereby the internal void spaces and micropores of never-dried Kraft pulp fibre walls were impregnated with silica. This was achieved by initial dehydration of never-dried fibre through azeotropic distillation to achieve substitution of fibre water with the silicon chemical solution over a range of concentrations. Kraft fibres were stiffened and made resistant to collapse from the effect of the azeotrope drying. Specific chemical reaction of azeotrope-dried fibre with the reagent ClSi(OEt)3 followed by base-catalysed hydrolysis of the ester groups formed a fibre-bound silica composite. The physico-chemical substitution of water from micropores and internal voids of never-dried fibre with property-modifying chemicals offers possibilities in the development of new fibre characteristics, including fibres which may be hardened, plasticised, and/or stabilised against moisture, biodegradation or fire. The embedded silica may also be used as sites of attachment for coupling agents to modify the hydrophilic character of the fibre or to functionalise the fibre surface

The effect of irregular breathing patterns on internal target volumes in four-dimensional CT and cone-beam CT images in the context of stereotactic lung radiotherapy

Purpose: Stereotactic lung radiotherapy is complicated by tumor motion from patient respiration. Four-dimensional CT (4DCT) imaging is a motion compensation method used in treatment planning to generate a maximum intensity projection (MIP) internal target volume (ITV). Image guided radiotherapy during treatment may involve acquiring a volumetric cone-beam CT (CBCT) image and visually aligning the tumor to the planning 4DCT MIP ITV contour. Moving targets imaged with CBCT can appear blurred and currently there are no studies reporting on the effect that irregular breathing patterns have on CBCT volumes and their alignment to 4DCT MIP ITV contours. The objective of this work was therefore to image a phantom moving with irregular breathing patterns to determine whether any configurations resulted in errors in volume contouring or alignment. Methods: A Perspex thorax phantom was used to simulate a patient. Three wooden "lung" inserts with embedded Perspex "lesions" were moved up to 4 cm with computer-generated motion patterns, and up to 1 cm with patient-specific breathing patterns. The phantom was imaged on 4DCT and CBCT with the same acquisition settings used for stereotactic lung patients in the clinic and the volumes on all phantom images were contoured. This project assessed the volumes for qualitative and quantitative changes including volume, length of the volume, and errors in alignment between CBCT volumes and 4DCT MIP ITV contours

Assessment of leakage dose in vivo in patients undergoing radiotherapy for breast cancer

Background and purpose Accurate quantification of the relatively small radiation doses delivered to untargeted regions during breast irradiation in patients with breast cancer is of increasing clinical interest for the purpose of estimating long-term radiation-related risks. Out-of-field dose calculations from commercial planning systems however may be inaccurate which can impact estimates for long-term risks associated with treatment. This work compares calculated and measured dose out-of-field and explores the application of a correction for leakage radiation. Materials and methods Dose calculations of a Boltzmann transport equation solver, pencil beam-type, and superposition-type algorithms from a commercial treatment planning system (TPS) were compared with in vivo thermoluminescent dosimetry (TLD) measurements conducted out-of-field on the contralateral chest at points corresponding to the thyroid, axilla and contralateral breast of eleven patients undergoing tangential beam radiotherapy for breast cancer. Results Overall, the TPS was found to under-estimate doses at points distal to the radiation field edge with a modern linear Boltzmann transport equation solver providing the best estimates. Application of an additive correction for leakage (0.04% of central axis dose) improved correlation between the measured and calculated doses at points greater than 15 cm from the field edge. Conclusions Application of a correction for leakage doses within peripheral regions is feasible and could improve accuracy of TPS in estimating out-of-field doses in breast radiotherapy

Improvement of neuropathology and transcriptional deficits in CAG 140 knock-in mice supports a beneficial effect of dietary curcumin in Huntington's disease

<p>Abstract</p> <p>Backgound</p> <p>No disease modifying treatment currently exists for Huntington's disease (HD), a fatal neurodegenerative disorder characterized by the formation of amyloid-like aggregates of the mutated huntingtin protein. Curcumin is a naturally occurring polyphenolic compound with Congo red-like amyloid binding properties and the ability to cross the blood brain barrier. CAG140 mice, a knock-in (KI) mouse model of HD, display abnormal aggregates of mutant huntingtin and striatal transcriptional deficits, as well as early motor, cognitive and affective abnormalities, many months prior to exhibiting spontaneous gait deficits, decreased striatal volume, and neuronal loss. We have examined the ability of life-long dietary curcumin to improve the early pathological phenotype of CAG140 mice.</p> <p>Results</p> <p>KI mice fed a curcumin-containing diet since conception showed decreased huntingtin aggregates and increased striatal DARPP-32 and D1 receptor mRNAs, as well as an amelioration of rearing deficits. However, similar to other antioxidants, curcumin impaired rotarod behavior in both WT and KI mice and climbing in WT mice. These behavioral effects were also noted in WT C57Bl/6 J mice exposed to the same curcumin regime as adults. However, neither locomotor function, behavioral despair, muscle strength or food utilization were affected by curcumin in this latter study. The clinical significance of curcumin's impairment of motor performance in mice remains unclear because curcumin has an excellent blood chemistry and adverse event safety profile, even in the elderly and in patients with Alzheimer's disease.</p> <p>Conclusion</p> <p>Together with this clinical experience, the improvement in several transgene-dependent parameters by curcumin in our study supports a net beneficial effect of dietary curcumin in HD.</p

A hybrid radiation detector for simultaneous spatial and temporal dosimetry

In this feasibility study an organic plastic scintillator is calibrated against ionisation chamber measurements and then embedded in a polymer gel dosimeter to obtain a quasi-4D experimental measurement of a radiation field. This hybrid dosimeter was irradiated with a linear accelerator, with temporal measurements of the dose rate being acquired by the scintillator and spatial measurements acquired with the gel dosimeter. The detectors employed in this work are radiologically equivalent; and we show that neither detector perturbs the intensity of the radiation field of the other. By employing these detectors in concert, spatial and temporal variations in the radiation intensity can now be detected and gel dosimeters can be calibrated for absolute dose from a single irradiation

Efficient Allele-Specific Targeting of LRRK2 R1441 Mutations Mediated by RNAi

Since RNA interference (RNAi) has the potential to discriminate between single nucleotide changes, there is growing interest in the use of RNAi as a promising therapeutical approach to target dominant disease-associated alleles. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been linked to dominantly inherited Parkinson's disease (PD). We focused on three LRRK2 mutations (R1441G/C and the more prevalent G2109S) hoping to identify shRNAs that would both recognize and efficiently silence the mutated alleles preferentially over the wild-type alleles. Using a luciferase-based reporter system, we identified shRNAs that were able to specifically target the R1441G and R1441C alleles with 80% silencing efficiency. The same shRNAs were able to silence specifically mRNAs encoding either partial or full-length mutant LRRK2 fusion proteins, while having a minimal effect on endogenous wild-type LRRK2 expression when transfected in 293FT cells. Shifting of the mutant recognition site (MRS) from position 11 to other sites (4 and 16, within the 19-mer window of our shRNA design) reduced specificity and overall silencing efficiency. Developing an allele-specific RNAi of G2019S was problematic. Placement of the MRS at position 10 resulted in efficient silencing of reporters (75–80%), but failed to discriminate between mutant and wild-type alleles. Shifting of the MRS to positions 4, 5, 15, 16 increased the specificity of the shRNAs, but reduced the overall silencing efficiency. Consistent with previous reports, these data confirm that MRS placement influences both allele-specificity and silencing strength of shRNAs, while further modification to hairpin design or MRS position may lead to the development of effective G2019S shRNAs. In summary, the effective shRNA against LRRK2 R1441 alleles described herein suggests that RNAi-based therapy of inherited Parkinson's disease is a viable approach towards developing effective therapeutic interventions for this serious neurodegenerative disease

Prevención de accidentes laborales para el personal eléctrico que realiza adecuación en estación transformadora

Se tiene conocimiento de que hoy en día se siguen evidenciando accidentes laborales y enfermedades profesionales por diversas causas. El tema en estudio se enfoca en indagar sobre aquellos riesgos que se derivan de las tareas que ejecutan los oficiales especializados eléctricos en la actividad de Adecuación en Subestación Transformadora Eléctrica; tomando conocimiento de cuáles son los accidentes y/o enfermedades profesionales que se producen con mayor frecuencia, como se abordan cada una de las diligencias, métodos de aplicación de las normas de seguridad, que procedimientos e instructivos operativos se emplean tanto de la empresa en cuestión como del cliente, cuales herramientas, equipos, maquinarias y elementos de protección personal son necesarios para la ejecución de la labor y de allí implementar un plan de mejoras para reducir y/o eliminar dichos riesgos

Systematic variations in polymer gel dosimeter calibration due to container influence and deviations from water equivalence

There are a number of gel dosimeter calibration methods in contemporary usage. The present study is a detailed Monte Carlo investigation into the accuracy of several calibration techniques. Results show that for most arrangements the dose to gel accurately reflects the dose to water, with the most accurate method involving the use of a large diameter flask of gel into which multiple small fields of varying dose are directed. The least accurate method was found to be that of a long test tube in a water phantom, coaxial with the beam. The large flask method is also the most straightforward and least likely to introduce errors during setup, though, to its detriment, the volume of gel required is much more than other methods