Samarium-Doped Fluorophosphate and Fluoroaluminate Glasses for High-Dose High-Resolution Dosimetry for Microbeam Radiation Therapy
Date
2020-05-19
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-4360-714X
Type
Thesis
Degree Level
Doctoral
Abstract
Microbeam Radiation Therapy (MRT) is an important and developing radiotherapy technique that uses spatially fractionated doses, several orders of magnitude larger than that of the doses used in conventional radiation therapy. Healthy tissue displays remarkable resistance to damage caused from microscopically narrow, fractionated, planar beams of x-rays, while showing preferential damage towards cancerous growths, allowing for a high potential towards the treatment of often inoperable tumours. These synchrotron generated, spatially fractionated, planar beams are referred to as microbeams, and have a thickness of 20 – 50 µm and are separated by distances of 100 – 400 µm. The dose delivered at the center of the microbeam can be on the order of thousands of Grays (Gy), whereas the dose between each microbeam should be kept below tens of Gy. An important aspect of MRT is the spatial distribution of the dose delivered to the patient, which must be accurately measured. Ultimately, both high resolution and large dynamic range dosimetric measurements must be done simultaneously.
The objective of this Ph.D. research involves the development and characterization of a dosimetric technique that fulfills the requirements of measuring dose distributions of microbeams. The proposed technique uses the indirect detection of x-rays, where the dose is recorded in a glass plate which can then be readout using a confocal microscopy system. The dose delivered is recorded by using trivalent samarium (Sm3+) doped fluoroaluminate and fluoro-phosphate glasses, where conversion from the trivalent form of samarium to the divalent form (Sm2+) occurs after exposure to x-rays. The extent of this conversion can be readout and digitized with high resolution using a confocal microscopy system that utilizes the easily distinguishable photoluminescent spectra of Sm3+ to Sm2+.
The work carried out in this research involves the high resolution recording of microbeam profiles performed at the Canadian synchrotron, using samarium doped glass plates under a variety of irradiation parameters in order to determine their suitability for dosimetric applications. In particular, the dose rate and x-ray energy dependence of these materials is investigated, as well as the determination of the optimum Sm3+ dopant concentration. Further, the confocal measurement technique is investigated, as well as the suitability of ion implantation of samarium ions in order to improve the signal readout. Lastly, the change in dose distributions of microbeams is investigated by performing irradiations over a wide range of monochromatic x-rays, so that the potential effect of the selected energy on MRT treatment planning can be examined.
Description
Keywords
Microbeam Radiation Therapy, Dosimetry, Rare earth ions, Radiation detection
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Biomedical Engineering
Program
Biomedical Engineering