Doctor of Philosophy
School of Physics
Radiation therapy for cancer now includes several, significantly different techniques. To ensure treatment quality, both in terms of safety and efficacy, each technique requires the use of numerous, customized devices. This thesis considered two such devices, designed at the Centre of Medical Radiation Physics, University of Wollongong, and investigated their applications in scenarios that are particularly challenging in modern x-rays external-beam radiation therapy.
The first device was a metal-oxide-semiconductor field-effect transistor (MOSFET) named MOSkin. The MOSkin was first introduced to address the longstanding challenge of measuring radiation dose to the skin of a patient. Other existing sensors were not able to measure accurately in that context, and calculations with a treatment planning system were known to be not adequate. In this thesis, the first step was to look into the MOSkin seeking to optimize its design, so that it could be used to measure dose to the skin of a patient who requires medical imaging with ionizing radiation. Examples of that imaging include image-guided radiation therapy, but also a range of procedures used for diagnostic radiology. The second step was to look into the MOSkin as a device to evaluate a novel bolus. The bolus can be applied on the skin of a patient during x-rays radiation therapy, to provide additional dose build-up and ensure high dose is delivered to the superficial regions.
The second device was a two-dimensional monolithic array of silicon diodes named Octa. The Octa was first introduced to address the challenge of measuring two-dimensional dose distribution, with a spatio-temporal resolution commensurate with stereotactic x-rays radiation therapy. Stereotactic treatments deliver radiation beams in arcs around the patient so, in this thesis, the first step was to look into the sensitivity of the Octa changes as a function of radiation’s angle of incidence. This investigation was also necessary to prepare for the second step, which looked into the Octa as a quality assurance device in the specific case of stereotactic body radiation therapy for vertebral metastases. The Octa was considered a good candidate to map the two-dimensional distribution of radiation dose across the vertebrae, and surrounding organs at risk such as the spinal cord, demonstrating steep dose gradients were delivered to the patient as prescribed.
The present thesis demonstrated that (1) the MOSkin design can be optimized for measuring dose to the skin of a patient who requires medical imaging that use ionizing radiation and that (2)the MOSkin can be used to evaluate the suitability of novel bolus for clinical use. Design optimization was achieved using sensitive volumes of a different thickness. The present thesis also demonstrated that (3) the Octa sensitivity to radiation is angularly dependent, but that this dependence can be characterized and accounted for, and that (4) the Octa can be considered as a good candidate to ensure the quality of stereotactic body radiation therapy for vertebral metastases.
Al-sudani, Taghreed, Integrated dosimetry for quality assurance in advanced radiation therapy, Doctor of Philosophy thesis, School of Physics, University of Wollongong, 2021. https://ro.uow.edu.au/theses1/1194
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.