Gel-phantom study for target volume optimization in HDR and/or LDR brachytherapy using advanced imaging techniques

In this thesis, agar, agarose, and polyvinyl alcohol cryogel phantoms with concentrations ranging from 1.0% to 3.5%, 0.5% to 3.0%, and 10% to 20%, respectively, were prepared to create tissue-mimicking gel phantoms convenient for Diffusion Kurtosis Imaging (DKI) in order to develop proper sequences for target volume optimization in High Dose Rate (HDR) and/or Low Dose Rate (LDR) brachytherapy. The kurtosis values of the gels increased with the concentration but they were too low to mimic values for various tissues when created purely. Therefore, glass microspheres were added into the gels at different concentrations to create tissue-mimicking phantoms with more realistic kurtosis values. Diffusion coefficients (ADC or D(1) and D(2)), excess kurtosis (K) values, and relaxation parameters were experimentally determined and the kurtosis values for the plain gels ranged from 0.05 (0.029, 0.071) to 0.216 (0.185, 0.246) with 95% confidence interval (CI). Inclusion of glass microspheres increased the kurtosis with values up to 0.523 (0.465, 0.581) observed for gels with the highest concentration of microspheres. The presence of glass microspheres reduced ADCs and increased the transverse and longitudinal relaxation rates. Phantoms were also evaluated for the further physical parameters using X-ray Computed Tomography (CT) and Ultrasound (US) elastography. The study shows that agar gels including glass microspheres in particular are encouraging materials as low-cost and durable phantoms for Diffusion Weighted-Magnetic Resonance Imaging (DW-MRI) and DKI with tuneable diffusion and relaxation properties.