Advanced Methods for Radiation Protection in Medical and Space Applications
Creators: name: Large, Matthew
Publisher: name: University of Wollongong
Year: 2025
Subjects: classificationCode: 510106
subject: High energy astrophysics and galactic cosmic rays
classificationCode: 510502
subject: Medical physics
classificationCode: 511002
subject: Instruments and techniques
classificationCode: 321110
subject: Radiation therapy

description: There is a growing demand for the development of innovative materials and methods to accurately determine the radiation dose delivered to humans. This demand extends to a diverse range of applications including nuclear science, defence, personal dosimetry, medical imaging and radiotherapy, and space exploration.The radiation environment of space is arguably one of the largest risks to astronauts, be it on the International Space Station (ISS), or for future planned deep space missions to the Moon and Mars. In particular, characterising the radiation environment on the surface of the Moon is of great interest within the radiation protection community, as NASA plans to establish a Lunar Gateway and return humans to the Moon for the first time since the 1970s. This is encompassed within NASA’s ARTEMIS missions, where Australia is also contributing through the development of a rover for lunar surface explorations. Therefore, dosimetry measurements are pivotal in assessing the potential risks to electronic components and the radiation-induced biological effects within humans. Experimental measurements are essentially impossible to perform due to the cost of access in space and limited data from previous missions to the Moon. In this case, the utilisation of simulation studies provide a cost-effective means of conducting such assessments. This thesis summarises the results of simulation studies performed to characterise the secondary radiation backscattered from the lunar surface, as well as estimate the daily absorbed doses that can be expected in radio-sensitive organs within the human body.In addition to the complex radiation environment of space, clinical radiotherapy environments require dosimetry methods that can provide accurate and real-time evaluations of patient safety and treatment efficacy. New advancements in radiotherapy treatments have resulted in the need for novel detector technologies with improved performances. These advancements include particle and heavy ion therapies, high dose-rate radiotherapy, and the adaptation of in vivo dosimetry practices for improved patient safety. To address these challenges, novel radiation dosimeters are characterised throughout this study. The detector solutions explored are fabricated from either hydrogenated amorphous silicon (a-Si:H) or organic semiconductor technologies, both of which offer a variety of benefits (such as cheaper manufacturing) compared to traditional solid state devices employing crystalline silicon, germanium or cadmium zinc telluride.The characterisation of these detectors for X-ray dosimetry is presented for both current and emerging External Beam Radiation Therapy (EBRT) treatment modalities. This thesis presents the first characterisations of a-Si:H diode structures on flexible substrates for therapeutic X-ray beams. Potential applications include fully-flexible and minimally perturbing detector solutions for in vivo dosimetry. To achieve this, novel semiconducting materials are explored which provide benefits over currently employed solid-state detector solutions. Organic photodiodes, coupled with plastic scintillators, offer flexibility and improved tissue equivalence in comparison to silicon. Furthermore, the a-Si:H detectors explored in this thesis display superior radiation tolerances in addition to fully flexible detector solutions, identifying them as suitable candidates for prolonged radiation exposures during clinical radiotherapy applications.For a-Si:H detectors, their applications as dosimeters are extended to novel treatment modalities combining high dose-rates and micron-scale spatial fractionation of the treatment beam in a modality known as Microbeam Radiation Therapy. This thesis is the first to document the application of a-Si:H as a solution for beam monitoring and dosimetry of microbeam treatment modalities at synchrotron facilities.