A simulation study of BrachyShade, a shadow-based internal source tracking system for HDR prostate brachytherapy

© 2018 Commonwealth of Australia. Department of Education and Training, and Department of Industry, Innovation and Science.. This paper presents a simulation study of BrachyShade, a proposed internal source-tracking system for real time quality assurance in high dose rate prostate brachytherapy. BrachyShade consists of a set of spherical tungsten occluders located above a pixellated silicon photodetector. The source location is estimated by minimising the mean squared error between a parametric model of the shadow image and acquired images of the shadows projected on the detector plane. A novel algorithm is finally employed to correct the systemic error resulting from Compton scattering in the medium. The worst-case error obtained with BrachyShade for a 13.5 ms image acquisition is less than 1.3 mm in the most distant part of the treatment volume, while for 75% of source locations an error of less than 0.42 mm was achieved

Wilt disease symptoms in red leaf lettuce (Lactuca sativa L.) after inoculated with Trichoderma longibrachiatum

Trichoderma is a fungal genus that is widely reported to cause beneficial impacts to crop plants but rarely detriment. The present study was conducted to assess the effect of inoculation of Trichoderma longibrachiatum strain UPMT14 on red leaf lettuce (Lactuca sativa L.) under growth room conditions. A culture of UPMT14 was grown on potato dextrose broth to produce inoculum. This liquid inoculum was injected through the stem of red leaf lettuce seedlings 22 days old with five replications, and then plant growth progress was monitored for vegetative responses. Red leaf lettuce plants began to exhibit foliar symptoms on day 36, such as chlorosis, wilt, and drying out, before total collapsed on day 45 in comparison to untreated control red leaf lettuce plants. In conclusion, the wilting incidence in red leaf lettuce was observed after T. longibrachiatum inoculation. Further studies are needed in future to understand the pathogenesis of T. longibrachiatum

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems

© 2015 Institute of Physics and Engineering in Medicine. A common approach to improving the spatial resolution of small animal PET scanners is to reduce the size of scintillation crystals and/or employ high resolution pixellated semiconductor detectors. The large number of detector elements results in the system matrix - an essential part of statistical iterative reconstruction algorithms - becoming impractically large. In this paper, we propose a methodology for system matrix modelling which utilises a virtual single-layer detector ring to greatly reduce the size of the system matrix without sacrificing precision. Two methods for populating the system matrix are compared; the first utilises a geometrically-derived system matrix based on Siddon's ray tracer method with the addition of an accurate detector response function, while the second uses Monte Carlo simulation to populate the system matrix. The effectiveness of both variations of the proposed technique is demonstrated via simulations of PETiPIX, an ultra high spatial resolution small animal PET scanner featuring high-resolution DoI capabilities, which has previously been simulated and characterised using classical image reconstruction methods. Compression factors of and are achieved using this methodology for the system matrices produced using the geometric and Monte Carlo-based approaches, respectively, requiring a total of 0.5-1.2 GB of memory-resident storage. Images reconstructed from Monte Carlo simulations of various point source and phantom models, produced using system matrices generated via both geometric and simulation methods, are used to evaluate the quality of the resulting system matrix in terms of achievable spatial resolution and the CRC, CoV and CW-SSIM index image quality metrics. The Monte Carlo-based system matrix is shown to provide the best image quality at the cost of substantial one-off computational effort and a lower (but still practical) compression factor. Finally, a straightforward extension of the virtual ring method to a three dimensional virtual cylinder is demonstrated using a 3D DoI PET scanner

Ammonia volatilization from urea at different levels of zeolite.

Ammonia (NH3) loss due to hydrolysis of urea can be substantial. When applied to the soil, up to 50% NH3 volatilizes. This decreases urea-N use efficiency. The objective of this study was to minimize ammonia loss from urea using different levels of clinoptilolite zeolite. Six treatments were evaluated; (1) soil alone, (2) 2.60 g granular urea, (3) 2.60 g liquid urea, (4) 2.60 g liquid urea + 4 g of zeolite, (5) 2.60 g liquid urea + 8 g of zeolite and (6) 2.60 g liquid urea + 12 g of zeolite. The incubation study was conducted using close-dynamic air flow system method to measure the amount of NH3 released. At the end of this study, soils samples were analyzed for pH, exchangeable ammonium (NH4+) and available nitrate (NO3-) using standard procedures. When urea was applied in liquid form, NH3 loss was reduced when compared with granular urea, but not significantly different among the treatments with and without zeolite inclusion. Increase in soil pH was observed upon addition of higher amount of zeolite when compared with urea alone. High NH4+ content and low NH3 loss for T5 directly showed that high cation exchange capacity (CEC) of the amended soil due to inclusion of zeolite was responsible for retention of more NH4+ in the soil even though the soil pH was higher when compared with T1 and T2. Liquid urea mixed with zeolite reduced NH3 loss and increased NH4+ retention in the soil

Analytical Modelling and Simulation of Single and Double Cone Pinholes for Real-Time In-Body Tracking of an HDR Brachytherapy Source

© 2016 IEEE. The choice of pinhole geometry is a critical factor in the performance of pinhole-collimator-based source tracking systems for brachytherapy QA. In this work, an analytical model describing the penetrative sensitivity of a single-cone pinhole collimator to photons emitted from a point source is derived. Using existing models for single-cone resolution and double-cone sensitivity and resolution, the theoretical sensitivity and resolution of the single-cone collimator are quantitatively compared with those of a double-cone collimator with an equivalent field of view. Monte Carlo simulations of the single and double-cone pinhole collimators using an accurate 3D model of a commercial high dose rate brachytherapy source are performed to evaluate the relative performance of each geometry for a novel real-time HDR brachytherapy QA system, HDR BrachyView. The theoretical penetrative sensitivity of the single-cone pinhole is shown to be higher than the double-cone pinhole, which is in agreement with the results from the Monte Carlo simulations. The wider pinhole response function of the single-cone collimator results in a larger total error between the projected center of the source and the estimated center of mass of the source projection for the single-cone collimator, with the greatest error (at the maximum FoV angle) being 0.54 mm for the double-cone pinhole and 1.37 mm for the single-cone at θ = 60°. The double-cone pinhole geometry is determined to be the most appropriate choice for the pinhole collimator in the HDR BrachyView probe

Antagonistic activities of endophytic bacteria against Fusarium wilt of black pepper (Piper nigrum).

Fusarium wilt is a fungal disease, which affects a broad range of plants including black pepper (Piper nigrum). Fusarium solani f. sp. piperis is a common causal agent of root rots and stem blight in black pepper. F. oxysporum Schl. f. sp. piperis, a less common but an important pathogen of black pepper. The biological approach to control F. oxysporum is becoming popular in many crop plants however there is lack of scientific record in black pepper. Endophytic bacteria were isolated from black pepper roots and cultured on nutrient agar. The bacterial isolates were screened for in vitro antagonistic activity against F. oxysporum through dual culture, mycelial growth, spore germination and double plate tests. Five isolates with promising antifungal activity were further identified through 16S rDNA sequencing. Isolates EB1 and EB2 showed highest antagonism against F. oxysporum mycelia with the percentage of inhibition up to 43% and 41%, respectively. Isolated EB3, EB4 and EB5 produced clearing zones in spore germination test with radii measurements at 12.5-15.0 mm. The antifungal activities apparently involved the secretion of volatile and diffusible bioactive compounds. Analysis of the 16S rDNA sequences suggested the closest identities of the bacterial isolates as Bacillus megaterium, Bacillus cereus, Enterobacter sp. and Bacillus sp. Five endophytic bacteria isolates demonstrated significant control over both mycelia growth and spore germination of F. oxysporum. Some of these bacteria might possess additional beneficial plant growth promoting and insecticidal properties for the development of multi-function products in black pepper farming

Isolation of indigenous strains of Paecilomyces lilacinus with antagonistic activity Meloidogyne incognita.

Ten indigenous isolates of Paecilomyces lilacinus (PL), were isolated from two black pepper farms in Sarawak heavily infested with root-knot nematodes (RKN) as an initiative to control RKN problem. All isolates showed varying degree in colonizing female nematodes. In the female nematode bioassay on water agar, both indigenous strains of PL namely PLA, PLB, and a commercial strain, PLM (as positive control) demonstrated highly significant colonization (>90%, P≤0.01) on female. In egg parasitism test, spore suspension (105 spore/mL) of the strains PLA, PLB and PLM exhibited 78.8%, 66.0% and 73.4% parasitism on eggs, respectively. Meanwhile, hatching of nematode eggs incubated in spore suspension of PLA, PLB and PLM for seven days were significantly reduced; 88-89% of eggs were hatch-inhibited as compared to control (26%). This illustrated both local isolates, PLA and PLB are comparable with PLM as biological control agents for managing RKN infestation on black pepper vines

BrachyView, a novel in-body imaging system for HDR prostate brachytherapy: Experimental evaluation

© 2015 American Association of Physicists in Medicine. Purpose: This paper presents initial experimental results from a prototype of high dose rate (HDR) BrachyView, a novel in-body source tracking system for HDR brachytherapy based on a multipinhole tungsten collimator and a high resolution pixellated silicon detector array. The probe and its associated position estimation algorithms are validated and a comprehensive evaluation of the accuracy of its position estimation capabilities is presented. Methods: The HDR brachytherapy source is moved through a sequence of positions in a prostate phantom, for various displacements in x, y, and z. For each position, multiple image acquisitions are performed, and source positions are reconstructed. Error estimates in each dimension are calculated at each source position and combined to calculate overall positioning errors. Gafchromic film is used to validate the accuracy of source placement within the phantom. Results: More than 90% of evaluated source positions were estimated with an error of less than one millimeter, with the worst-case error being 1.3 mm. Experimental results were in close agreement with previously published Monte Carlo simulation results. Conclusions: The prototype of HDR BrachyView demonstrates a satisfactory level of accuracy in its source position estimation, and additional improvements are achievable with further refinement of HDR BrachyView's image processing algorithms

Radiation dose enhancement at tissue-tungsten interfaces in HDR brachytherapy

© 2014 Institute of Physics and Engineering in Medicine. HDR BrachyView is a novel in-body dosimetric imaging system for real-time monitoring and verification of the source position in high dose rate (HDR) prostate brachytherapy treatment. It is based on a high-resolution pixelated detector array with a semi-cylindrical multi-pinhole tungsten collimator and is designed to fit inside a compact rectal probe, and is able to resolve the 3D position of the source with a maximum error of 1.5 mm. This paper presents an evaluation of the additional dose that will be delivered to the patient as a result of backscatter radiation from the collimator. Monte Carlo simulations of planar and cylindrical collimators embedded in a tissue-equivalent phantom were performed using Geant4, with an 192Ir source placed at two different source-collimator distances. The planar configuration was replicated experimentally to validate the simulations, with a MOSkin dosimetry probe used to measure dose at three distances from the collimator. For the cylindrical collimator simulation, backscatter dose enhancement was calculated as a function of axial and azimuthal displacement, and dose distribution maps were generated at three distances from the collimator surface. Although significant backscatter dose enhancement was observed for both geometries immediately adjacent to the collimator, simulations and experiments indicate that backscatter dose is negligible at distances beyond 1 mm from the collimator. Since HDR BrachyView is enclosed within a 1 mm thick tissue-equivalent plastic shell, all backscatter radiation resulting from its use will therefore be absorbed before reaching the rectal wall or other tissues. dosimetry, brachytherapy, HD