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Dosimetry is the methodology of determining the amount of radiation energy imparted in matter and volume. Although several techniques and devices are available for use in both laboratory and clinical settings, most rely on certain conditions, assumptions and approximations to convert the energy into radiation dose. The many uncertainties from current techniques are introduced due to the material differences between the sensitive detector volume and the phantom material, typically water. The aim of this thesis is to use the water sample itself to detect the amount of radiation energy that has been imparted upon it. Radiation energy absorbed by the sample is ultimately converted into heat, raising the temperature of the sample and changing the refractive index property. The refractive index change results in a shortening of the optical path length and as a result, light passing through the sample experiences a phase change. Phase information cannot be directly measured, as it is merely a property of light wave propagation, thus another technique must be used. Digital holographic interferometry was employed to capture snapshots of the sample’s changing state over time, and when compared with a reference, the interference phase information was extracted and used to calculate the refractive index change, which can then be related to radiation absorbed dose. The aim of this research was to design and build interferometry setups using holographic interferometry to determine the refractive index change induced by radiation and to explore the possibilities of using fibre optics. Experiments were conducted on the setups to determine the validity of the method and the accuracy of the system. With external heating sources in the forms of an open flame and infrared laser, we could see distinct heating patterns formed in the phase images. The phase allowed the calculation of the temperature and therefore energy from the change in refractive index, but was limited to phase differences within 2π between the images, due to wrapped phases. In the stability tests, we demonstrated the accuracy of the system and found it was heavily influenced by the amount of vibration in the vicinity. In the short term, a standard deviation of 0.015 degrees was recorded but a larger standard deviation of 0.078 degrees was measured in the longer term. We can be confident of the temperature measurements to within 0.1 of a degree, equal to hundreds of Grays in radiation dose, however this is not sufficiently accurate for dosimetry. Future work may include improving accuracy by reducing the vibration in the system.

Lyoluminescence (LL) of the phosphors glutamine and mannose was used to determine instrument stability, reproducibility of readings, sensitivity and lowest detectable dose in order to evaluate the performance of the Aberdeen LL Research Reader (before and after modifications) and compare it with commercially available luminometers. The dependence of the LL yield on mass of dissolved glutamine, the sample's irradiation temperature, and solvent temperature were investigated and correction factors determined. Heat treatment was found to remove the dependence on pre- and post-irradiation storage time. Using aqueous LL dosimetry of glutamine, unknown doses in the range 10Gy to 3kGy were determined with overall accuracy and precision of 2% and 5% respectively during the 1982 IAEA Dose Intercomparison trials. Factors affecting the LL of mannose in water and methanol were compared, and a 20-fold increase in LL yield was reported using the latter solvent. Various attempts to enhance the LL yield from glutamine and mannose were made: Enhancements, of up to 10⁵ times, caused by the oxidation of luminol, lucigenin, lophine and trichlorophenol oxalate by the primary species in LL were observed, but increased background readings due to self-glow caused there to be no advantage in overall sensitivity. Enhancement factors (EF) up to 100 were obtained using glutamine LL in free and chelated rare earth ion solutions, as a result of intermolecular energy transfer from excited organic molecules in solution. However, the enhancement was found to be dose dependent. By employing dibromoanthracene sulphonate, rubrene, eosin and reduced lucigenin, all of which respond to singlet oxygen, EF of up to 10 were achieved in LL of mannose. Finally, as the use of aqueous solutions was found to severely limit the possible phosphor/enhancer combinations, the LL of some carboxylic acids in alcoholic media was investigated. These were found to be less sensitive LL phosphors than either mannose or glutamine.

The increasing use of intensity modulated radiation therapy (IMRT) to deliver conformal radiation treatment has prompted the search for a faster and more cost effective quality assurance (QA) system. The standard technique relies on the use of film for two-dimensional dose distribution verification. Although film is considered the gold standard and is widely used for this purpose, the procedures involved are relatively lengthy, labour intensive and costly for a multiple field IMRT verification. In this study, we investigate the use of an amorphous silicon electronic portal imaging device (a-Si EPID) to complement the film. The dosimetric behaviour of the device is studied both experimentally and numerically using the EGSnrc Monte Carlo simulation routine. The intrinsic build-up of the flat panel EPID was found to be 1.1 cm of water equivalent material. The response of the flat panel EPID was found to be linear between 0 and 300 cGy. To calibrate the flat panel EPID for two dimensional dose measurements, the deconvolution method was chosen. The scatter dose kernel required for this calibration method was calculated and characterized by varying the energy, spectrum and phantom material using a 6MV pencil beam. We found that flat panel EPID scatter kernel has as much as 80% more scattering power than the water scatter kernel in the region 1 cm away from the center of a 6MV pencil beam. This confirms that a flat panel EPID behaves significantly differently from water dosimetrically and requires an accurate dose scatter kernel for calibration. A 1.0 cm wide picket fence test pattern was used to test the accuracy of the kernel. Using the deconvolution method with the calculated dose kernels, the measurements from the flat panel EPID show improved agreement with the films.

This thesis investigates the response to ionising radiation, of p-type Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) (REM Oxford (UK)) and a reader system developed by the Centre for Medical Radiation Physics, The University of Wollongong, to determine their feasibility for measurements of dose during radiotherapy treatment (in vivo dosimetry (IVD)). Two types of MOSFET probes were used -"single sensitivity", for measuring low doses, and "dual sensitivity", to measure both high and lose doses. Sensitivity, linearity of response with dose, and response changes with accumulated dose and direction of incident radiation (angular dependence) were investigated. The average sensitivity reduction over the lifetime of the probes was 22.37% with a standard deviation of 0.63%. This reduction in sensitivity can be corrected for by the use of "drift equations". MOSFETs have a limited "lifetime" due to saturation effects with increasing accumulated dose. Saturation occurred at an average of 40 Gray (Gy) accumulated dose, for the high sensitivity probes investigated. The high sensitivity probes were linear within 1.6% for doses between 5 and 140 cGy, and 3.8% for the high sensitivity probes for doses between 50 and 500 cGy. Drift (changes in readings with time since irradiation due to electronic processes) over the long-term (from hours to weeks following irradiation) has been previously well characterised in the literature. This work focuses on shortterm drift, within the first few seconds or minutes following irradiation, being the most clinically relevant for in vivo measurements. Drift is investigated for various reading methods, such as reading frequency, and delays between irradiation and readings. It is shown that sensitivity, and consequently dose determination, is significantly influenced by the reading methodology. During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). When two post-irradiation readings were taken following an irradiation, the difference between them generally increased as the time interval between the two readings increased, by up to 8.8%. Delays in taking pre-and post-irradiation readings resulted in drift of up to 5.7% or 9.3% respectively, compared with readings without a delay. These results emphasise the necessity for consistent methodologies between calibration and measurement in the clinical situation. Greater sensitivity was measured with the epoxy bubble, rather than the substrate side, facing the beam. The greatest variation, for orientations other than the bubble side facing directly towards the beam, was 10%, or 5% uncertainty in dose. The variations with angle were found to be reproducible, so that appropriate correction factors could be applied to correct measurements at angles other than with the sensitive area of the probes facing directly towards the radiation beam. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1368262 / Thesis (M.Sc.) -- University of Adelaide, School of Chemistry and Physics, 2009

Radiation dosimetry is necessary for optimising radiation-based medical procedures for individual patients but in the field of nuclear medicine there are few widely available or widely used tools for performing this kind of analysis. Those tools that are available tend to focus on one particular component of the dosimetry problem and integrating tools to form a complete system is left to the end-user. A software system for performing individual, image-based dosimetry analysis of nuclear medicine studies has been developed and validated. The system consists of a suite of tools that use common file formats and data models. The tools can be integrated to form applications by means of a simple scripting system. One tool is a gamma camera simulator that can produce realistic images of dynamic activity distributions in planar or tomographic formats. Simulated imaging studies produced by this tool are used to validate the other tools in the system. In addition, the system implements a method of simulation assisted quantitation which is shown to achieve high accuracy in both software and physical phantom studies. The system is applied to the dosimetry of I-131 Lipiodol, a therapeutic agent used to treat primary and secondary cancers of the liver. Simulation studies are used to validate the analytic methods used. Studies of a series of patients, treated over a period 10 years, are retrospectively analysed using a selection of methods appropriate to the available data. The results of the analysis demonstrated a large range of lung doses from 1 to 10 Gy/GBq administered. The median absorbed dose in liver was 3 Gy (range 1 - 10 Gy) and the median absorbed dose in tumor was 19 Gy (range 5 - 84 Gy). The large individual variation reinforces the necessity of individualised dosimetry for treatment planning and follow up.

Thesis (Ph.D.) -- McMaster University, 2000. / Includes bibliographical references (leaves 215-223). Also available via World Wide Web.