title: Fast Monte Carlo Simulation of ⁹⁰Y Bremsstrahlung using a Kernel-based Photon Source

authors: Zakariah, Suhaili

subjects: Monte Carlo

abstract: In targeted radionuclide therapy using ⁹⁰Y, bremsstrahlung photons can be used for imaging and subsequently for absorbed dose estimation. Monte Carlo simulation is a reliable method to study bremsstrahlung imaging but it takes a long computation time as not all ⁹⁰Y disintegrations result in emission of a bremsstrahlung photon. Furthermore the electron transport simulation is particularly time consuming. This research proposes that bremsstrahlung photons produced from the decay of a ⁹⁰Y point source are replaced with a kernel-based photon source for faster Monte Carlo simulation.
This study is divided into three main parts. First, a ⁹⁰Y point source in a spherical water phantom is fully simulated using Monte Carlo simulation. The characteristics of the bremsstrahlung photons produced from the ⁹⁰Y decay are investigated. The full Monte Carlo simulation of ⁹⁰Y point source provides the relationships between the emission position, energy and emission angle of the bremsstrahlung photon. These are recorded as probability distribution functions (PDFs).
Then, a kernel-based photon source which comprises of an array of photon-emitting concentric spherical shells is developed. The energy spectrum and angular distributions of the emitted photons are defined for each shell using the PDFs obtained previously from the full ⁹⁰Y Monte Carlo simulation. The kernel-based photon source shows a very close approximation to the distribution of bremsstrahlung photons generated by the full Monte Carlo simulation of ⁹⁰Y point source if the shells are sufficiently closely spaced.
Finally, the accuracy and speed of the kernel-based photon source are evaluated. A simplified gamma camera model, which consists of a collimator and NaI(Tl) detector is simulated to obtain the point spread function (PSF) of the point source ‘image’. The PSF can be represented as a Gaussian function. Estimation of σ of the Gaussian function and thus the full-width half-maximum (FWHM) is used to compare the different kernel-based photon source models to represent a ‘real’ source generated by a full Monte Carlo ⁹⁰Y simulation. The results show that the FWHMs of the photon source with kernels are comparable to full Monte Carlo simulation of ⁹⁰Y point source. The FWHM determined for a photon point source with the spectrum of ⁹⁰Y bremsstrahlung underestimates the full Monte Carlo simulation of the true ⁹⁰Y point source. This demonstrates that it is important to account for the photons being emitted at a distance away from the source and all of the photons cannot be assumed to come from a single point. It is more computationally efficient to use this source model than the kernel-based photon sources as it has the shortest computation time, however it is quite inaccurate. Simplifying the kernel-based source by assuming the photon emission as isotropic reduces the accuracy of the model slightly, though the reduction in simulation time is sufficiently small that the more accurate anisotropic kernel should be preferred.
The kernel-based photon source proposed in this study can be used to accurately represent the bremsstrahlung photons produced from the beta decay of a ⁹⁰Y point source. This approach greatly improves the simulation speed by almost 30 times.

text: Fast Monte Carlo Simulation of ⁹⁰Y Bremsstrahlung using a Kernel-based Photon Source In targeted radionuclide therapy using ⁹⁰Y, bremsstrahlung photons can be used for imaging and subsequently for absorbed dose estimation. Monte Carlo simulation is a reliable method to study bremsstrahlung imaging but it takes a long computation time as not all ⁹⁰Y disintegrations result in emission of a bremsstrahlung photon. Furthermore the electron transport simulation is particularly time consuming. This research proposes that bremsstrahlung photons produced from the decay of a ⁹⁰Y point source are replaced with a kernel-based photon source for faster Monte Carlo simulation.
This study is divided into three main parts. First, a ⁹⁰Y point source in a spherical water phantom is fully simulated using Monte Carlo simulation. The characteristics of the bremsstrahlung photons produced from the ⁹⁰Y decay are investigated. The full Monte Carlo simulation of ⁹⁰Y point source provides the relationships between the emission position, energy and emission angle of the bremsstrahlung photon. These are recorded as probability distribution functions (PDFs).
Then, a kernel-based photon source which comprises of an array of photon-emitting concentric spherical shells is developed. The energy spectrum and angular distributions of the emitted photons are defined for each shell using the PDFs obtained previously from the full ⁹⁰Y Monte Carlo simulation. The kernel-based photon source shows a very close approximation to the distribution of bremsstrahlung photons generated by the full Monte Carlo simulation of ⁹⁰Y point source if the shells are sufficiently closely spaced.
Finally, the accuracy and speed of the kernel-based photon source are evaluated. A simplified gamma camera model, which consists of a collimator and NaI(Tl) detector is simulated to obtain the point spread function (PSF) of the point source ‘image’. The PSF can be represented as a Gaussian function. Estimation of σ of the Gaussian function and thus the full-width half-maximum (FWHM) is used to compare the different kernel-based photon source models to represent a ‘real’ source generated by a full Monte Carlo ⁹⁰Y simulation. The results show that the FWHMs of the photon source with kernels are comparable to full Monte Carlo simulation of ⁹⁰Y point source. The FWHM determined for a photon point source with the spectrum of ⁹⁰Y bremsstrahlung underestimates the full Monte Carlo simulation of the true ⁹⁰Y point source. This demonstrates that it is important to account for the photons being emitted at a distance away from the source and all of the photons cannot be assumed to come from a single point. It is more computationally efficient to use this source model than the kernel-based photon sources as it has the shortest computation time, however it is quite inaccurate. Simplifying the kernel-based source by assuming the photon emission as isotropic reduces the accuracy of the model slightly, though the reduction in simulation time is sufficiently small that the more accurate anisotropic kernel should be preferred.
The kernel-based photon source proposed in this study can be used to accurately represent the bremsstrahlung photons produced from the beta decay of a ⁹⁰Y point source. This approach greatly improves the simulation speed by almost 30 times.

year: 2011

title: Literature review on motor skill and physical activity in preschool children in New Zealand

authors: Ali, Ajmol

subjects: Physical Literacy

abstract: Children’s physical activity levels have decreased significantly over the past 20 - 30 years, coinciding with obesity rates reaching epidemic levels. There is little research into typically developing preschool (birth to 5 year-olds) child- ren’s physical activity, with the majority of research focusing on children at risk of motor skill or neurological deficiencies. This review examines current research into young children’s development, especially motor development and physical activity, the effectiveness of intervention programmes for pro- moting children’s physical development and the various methods used to as- sess physical development. A decrease in children’s physical activity levels has coincided with an increase in obesity rates. Further research is needed to de- termine culturally and contextually appropriate and effective interventions for preschool children. Areas for further research include preschool children’s physical activity, particularly in regards to movement guidelines and require- ments for this age-group and ways to overcome potential barriers to meeting physical activity requirements. Young children’s physical activity and motor skill proficiency may be an important predictor of later-life physically active behaviors. Physical literacy and physical activity interventions within early childhood education could potentially support academic skills as well as phy- sical skills and behaviors.

text: Literature review on motor skill and physical activity in preschool children in New Zealand Children’s physical activity levels have decreased significantly over the past 20 - 30 years, coinciding with obesity rates reaching epidemic levels. There is little research into typically developing preschool (birth to 5 year-olds) child- ren’s physical activity, with the majority of research focusing on children at risk of motor skill or neurological deficiencies. This review examines current research into young children’s development, especially motor development and physical activity, the effectiveness of intervention programmes for pro- moting children’s physical development and the various methods used to as- sess physical development. A decrease in children’s physical activity levels has coincided with an increase in obesity rates. Further research is needed to de- termine culturally and contextually appropriate and effective interventions for preschool children. Areas for further research include preschool children’s physical activity, particularly in regards to movement guidelines and require- ments for this age-group and ways to overcome potential barriers to meeting physical activity requirements. Young children’s physical activity and motor skill proficiency may be an important predictor of later-life physically active behaviors. Physical literacy and physical activity interventions within early childhood education could potentially support academic skills as well as phy- sical skills and behaviors.

year: 2017

title: Māori language resources and Māori initiatives for teaching and learning te reo Māori

authors: Greensill, Hineitimoana

abstract: As the most southerly member of the Polynesian languages, a sub-group of the widespread Austronesian language family (Harlow, 2007), te reo Māori has been the subject of substantial analysis, documentation, and analyses of its structure since first contact with Captain Cook in 1769 (Whaanga & Greensill, 2014). The history, trials and tribulations of te reo Māori in Aotearoa have been well documented (see, for example, Reedy, 2000; Spolsky, 2005; Waitangi Tribunal, 1986, 2011). The various reasons for the language’s decline has been an area of ongoing debate and critique by academics, researchers, linguists, language activists, parliamentarians and Māori in recent times (see, for example, Bauer, 2008; Benton, 2015; Higgins, Rewi, & Olsen-Reeder, 2014; Rata, 2007; Winitana, 2011).

text: Māori language resources and Māori initiatives for teaching and learning te reo Māori As the most southerly member of the Polynesian languages, a sub-group of the widespread Austronesian language family (Harlow, 2007), te reo Māori has been the subject of substantial analysis, documentation, and analyses of its structure since first contact with Captain Cook in 1769 (Whaanga & Greensill, 2014). The history, trials and tribulations of te reo Māori in Aotearoa have been well documented (see, for example, Reedy, 2000; Spolsky, 2005; Waitangi Tribunal, 1986, 2011). The various reasons for the language’s decline has been an area of ongoing debate and critique by academics, researchers, linguists, language activists, parliamentarians and Māori in recent times (see, for example, Bauer, 2008; Benton, 2015; Higgins, Rewi, & Olsen-Reeder, 2014; Rata, 2007; Winitana, 2011).

year: 2017