Abstract
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 SiO2 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 μm) making it particularly suitable for use in a variety of interface dosimetry situations and also for small radiotherapy fields. Using the Ge-doped SiO2 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 ≤ 4 x 4 cm for 6 MV energy produced by a Varian linear accelerator. Results are presented for Ge-doped SiO2 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 pm 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 μm core dopant diameter Ge-doped SiO2 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 cm x 4.0 cm at 1.5 and 5.0 cm depths in a solid-waterTM 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.