Access Type

Open Access Dissertation

Date of Award

January 2018

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Medical Physics

First Advisor

Michael Snyder

Abstract

Contrast enhanced kilovoltage radiotherapy could be a significant improvement over the standard of care in glioblastoma multiforme, but its potential benefit has been hindered by fears of insufficient dose falloff, high skin and skull dose, contrast delivery concerns, and high cost. This dissertation aims to address the validity of these fears.

Contrast delivery concerns are examined by assuming that sufficient dose can be safely delivered to the tumor. Iodine, gadolinium, and gold nanoparticle biological effect and delivery research is examined and the ideal contrast delivery methods are reported. Dose falloff and skull dose are then investigated through treatment planning and experimentation.

Our team has created, commissioned, and tested the first reported mechanism for delivering kilovoltage intensity modulated radiotherapy. This required the invention and production of a novel 6 x 6 cm2 multi-rod collimator (MRC) with an in-house control system. The MRC was mounted between a decommissioned portal imager and several phantoms loaded with radiochromic film. Plans were created and delivered, and the resulting films were analyzed.

Film results were examined for dose falloff and, for the Rando phantom, enhancement due to the presence of skull. Dose to the surface was found to be approximately 40% of maximum dose measured, with an increase to approximately 50% for anthropomorphic phantoms. While higher than the megavoltage dose, these results demonstrate that 40-50Gy could be delivered to a target even without contrast enhancement. Dose to the skull was found to be small enough to be clinically relevant, but well below the threshold for necrosis.

After factoring in an estimated twofold to threefold increase in dose at the tumor due to gold nanoparticle enhancement, it can be concluded that the kilovoltage beam is capable of producing a plan that is not considered clinically detrimental. Future work will involve actualizing the delivery of contrast to a glioblastoma multiforme tumor, applying arc therapies to minimize dose to the surface, and measuring for ourselves the dose enhancement produced by contrast enhancement.

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