Development And Dosimetry Of A Conformal Superficial Brachytherapy Device

Abstract

Shortly after their discovery in 1895, x-rays began to be used to treat dermatologic ailments and malignant tumors. Superficial brachytherapy is the process of using ionizing radiation to kill skin cancer cells and is the oldest form of radiation therapy. Advancements in technology and our understanding of how ionizing radiation interacts with matter have led to vast improvements in the quality and efficacy of care in cancer treatment. Contemporary radiation therapy techniques for the treatment of cutaneous malignancies are diverse. The most common radiation therapy modality is external beam radiation therapy with standard fractionation. Recently, there has been a resurgence in applying superficial brachytherapy techniques with the introduction to the market of high dose remote afterloading brachytherapy applicators and electronic brachytherapy units, which provide fast, reliable, and effective treatments. However, currently available commercial devices are limited in that they are incapable of providing patient-specific dose distributions. Addressing those limitations, a conformal superficial brachytherapy (CSBT) applicator was manufactured and rigorously tested. The applicator was designed to house between one and 19 yttrium-90 (90Y) beta-minus radiation sources. Each source was affixed to the distal end of one of 19 translatable rods, which allowed each of the sources to be moved in parallel with one another to varied locations. The goal of this work was to examine the capability of the CSBT applicator to deliver patient-specific treatments and to maximize the conformality of planned dose distributions to uneven surfaces. The work presented in this thesis relied heavily on Monte Carlo (MC) simulation and film-based measurement methods to determine dose rates. It was necessary to benchmark and validate the MC code to know its accuracy in simulating the novel 90Y source's dose rates. The CSBT source was characterized under standard treatment conditions. Next, examples of dose rate distributions from multiple sources are presented. Lastly, the clinical results of a murine model dose rate escalation study are presented. This work shows that, with the CSBT applicator, it is possible to deliver accurate and conformal dose to superficial tissue.