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Title: Silica fibre thermoluminescence measurements at high atomic number interfaces and for small radiotherapy fields
Author: Alalawi, Amani Ibrahim
ISNI:       0000 0004 5346 8010
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2014
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Over the last few decades, radiation therapy techniques have been greatly improved, with more complex radiation delivery systems such as intensity-modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT) being used to treat complex tumour shapes. This has greatly increased the demand for more accurate dosimetry systems to achieve better targeting of the treatment area while sparing the surrounding normal tissues. Ge-doped Si02 telecommunication optical fibres are a potential form of thermoluminescence (TL) dosimeter that offers excellent TL yield as well as high spatial resolution, the size of the optical fibre (typically ~ 100 )lm) making it particularly suitable for use in a variety of interface dosimetry situations and also for small radiotherapy fields. Using the Ge-doped Si02 optical fibres as a dosimeter, the work in this thesis aims to present measurement of the dose enhancement that can be obtained close to high atomic number media. For present purposes iodine and gold have been investigated as generators of photoelectrons using 250 kVp photons produced by a Gulmay orthovoltage x-ray machine. Additional investigation is made of the dosimetry of small photon field sizes :S 4 x 4 cm for 6 MV energy produced by a Varian linear accelerator. Results are presented for Ge-doped Si02 telecommunication optical fibres with different core diameters. These have first been characterised in terms of linearity, energy dependence and glow curve, good linearity to dose being obtained, the fibre with a 50 )lm core dopant diameter providing the greatest TL yield. Consequently, it was used for dose enhancement investigation with iodine and different thicknesses of gold' coated to the fibre i.e. 20, 40, 60, 80, and 100 nm thickness. The experimental results were favourably compared against Monte Carlo simulations with FLUKA and DOSRZnrc. The 50 )lm core dopant diameter Ge-doped Si02 optical fibres were also used for dosimetric study of field sizes of 1.0 cm x 1.0 cm, 2.0 cm x 2.0 cm, 3.0 cm x 3.0 cm and 4.0 cmx 4.0 cm at 1.5 and 5.0 cm depths in a solidwater ™ phantom. The measurements have been then compared with GafChromic film, a 2D array ion chamber as well as with MC simulations with DOSXYZnrc and FLUKA.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available