Radiotherapy Response Using Intravoxel Incoherent Motion Magnetic Resonance Imaging in Liver Patients Treated with Stereotactic Body Radiotherapy

Abstract

RADIOTHERAPY RESPONSE USING INTRAVOXEL INCOHERENT MOTION MAGNETIC RESONANCE IMAGING IN LIVER PATIENTS TREATED WITH STEREOTACTIC BODY RADIOTHERAPY By Benjamin Charles Lewis A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University. Virginia Commonwealth University, 2019. Director: Siyong Kim, Professor, Department of Radiation Oncology Magnetic resonance imaging is utilized as an important tool in radiation oncology for delineation of healthy and cancerous tissues, and evaluating the functionality of those tissues, structures, and organs. Currently, the clinical imaging protocol at Virginia Commonwealth University includes anatomical imaging for tissue and structure delineation, and to observe treatment induced changes. Diffusion weighted imaging (DWI) is also acquired for calculation of apparent diffusion coefficient (ADC) values to provide quantitative information on tissue diffusivity and microstructure. However, anatomical images and ADC values may not display the true extent of changes in tissue. This work seeks to further utilize the capabilities of MRI and expand its role in treatment response monitoring for liver cancer patients treated with stereotactic body radiotherapy (SBRT). To do so, an imaging protocol and image analysis methodology to evaluate treatment changes on preand post-treatment image sets was developed. An extension of DWI, termed intravoxel incoherent motion iv (IVIM) imaging, was utilized to quantitatively assess levels of perfusion and diffusion within the liver and tumor. Acquisition of high quality diffusion weighted images of the liver necessitated the development of an MR safe respiratory motion management device, which was designed, constructed and evaluated in this work. An imaging protocol was developed providing anatomical and functional images of the liver, acquired under breath hold, utilizing the respiratory motion management device. An IVIM parameter calculation and texture analysis workflow was developed using MATLAB, and applied to acquired data sets from multiple studies, including past clinical cases, investigator, healthy volunteer, and liver cancer patient. Differences in IVIM and texture analysis parameters were investigated for healthy and diseased tissue, and for select dose regions from preand post-treatment imaging sessions. Significant differences, at a voxel level, were found between healthy and diseased tissue, and preand post-treatment volumes, for multiple parameters, including apparent diffusion coefficient, pure diffusion, and perfusion, as well as for various texture features. Overall, this study showed the potential of IVIM and texture analysis to be used for discriminating between healthy and diseased tissues in the liver, and for indication of treatment response.