Date of Award

8-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Committee Member

Endre A. Takacs, Committee Chair

Committee Member

Delphine Dean

Committee Member

Brian C. Dean

Committee Member

Jian He

Abstract

Cancer is one of the leading causes of death in today's world and also accounts for a major share of healthcare expenses for any country. Our research goals are to help create a device which has improved accuracy and treatment times that will alleviate the resource strain currently faced by the healthcare community and to shed some light on the elementary nature of the interaction between ionizing radiation and living cells.

Stereotactic radiosurgery is the treatment of cases in intracranial locations using external radiation beams. There are several devices that can perform radiosurgery, but the Rotating Gamma System is relatively new and has not been extensively studied. It has much flexibility as it uses fewer radiation sources which are capable of moving around the patient, unlike other systems that employ virtually static sources. We propose two new working modes of the RGS that will enable it to further extend its operational capabilities. We have studied the operation of an RGS device at the Rotating Gamma Institute in Debrecen, Hungary and have developed a Monte Carlo model of the same. The simulation results of the normal modes of operation are in close agreement with clinical results, thus validating our model. We have then used this model to propose the Intensity Modulated Radiosurgery (IMRS) and the Speed Modulated Radiosurgery (SMRS) mode of the RGS. In both modes, we can see that the penumbra falls off sharply along one axis which is required for treating cases near critical organs. While the IMRS has a disadvantage of longer treatment times, it is absent from the SMRS mode.

Current governing bodies state that any amount of radiation, with no threshold amount, is harmful and must be avoided at any cost. While this assumption is safe for radiation safety considerations, there is growing scientific evidence that the situation is more complex at low doses. In the modern day, we are continually exposed to low-dose radiation. Diagnostic imaging is one of the major contributors for exposure to low-dose ionizing radiation with over 70 million scans performed annually in the US. This calls for the study of the effect that low-dose radiation has on cells. The scientific community is currently divided on the effect that low-dose radiation has on living cells as experiments have not been able to provide conclusive results. We have designed an incubator cabinet which allows the study of the effect of low-dose x-ray radiation on cells in a temperature- and atmospheric-composition-controlled, radiation-safe environment. We use bremsstrahlung radiation to excite quasi-monochromatic, fluorescent x-rays of a metal plate to act as a source that is used to irradiate biological samples. We have also installed a photon-counting detector to characterize the radiation incident on the cell cultures. By changing the tube current or by switching out the metal plates we are able to effectively change the dose rate, and the energy of the radiation, giving us the control to perform different experiments. Here, we have presented our device along with calculations that prove the capabilities of our device. We hope that future research will shine some light through the fog that currently engulfs radio-biology research in this radiation regime.

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