Medical Physics Research

Highly charged ion generated effects in biological samples

In order to better understand of the effects of low-dose soft x-ray irradiation on the human body, its potential use in the field of medicine, and understanding its effect on human space travel, an x-ray irradiation port is under construction for use with the Clemson University Electron Beam Ion Trap (CUEBIT). The port was designed to use the highly charged ions (HCI) produced by the CUEBIT to generate x-rays and irradiate biological samples, such as cancer cells or stem cells. HCI based x-ray sources are point-like and quasi-monochromatic therefore offer a unique and previously unexplored irradiation technique.

HCI are created in the CUEBIT and accelerated down a horizontal beam line under ultra-high vacuum (UHV) conditions. X-rays are produced in the neutralization of HCI on a 125 μm beryllium window. In order to irradiate the biological sample, the UHV environment of the HCI beam must be interfaced with the ambient environment of the sample. To maintain the integrity of the biological sample being studied, the custom vacuum chamber was designed to allow the sample to remain in a horizontal orientation. In order to do this, the horizontal HCI beam must be bent to a vertical direction toward the sample.

A custom interface was developed to position the cell culture dish directly above the beryllium window. The x-rays are low-energy, therefore the materials used are key. This is especially true for the cell culture dish because the x-rays must transmit through the bottom of the dish to irradiate the sample. To ensure maximum x-ray transmission and provide a sterile environment for healthy cell proliferation, thin-film mylar-bottom cell culture dishes were tested and implemented in this design.

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GEANT4 modeling of radiation interaction with cells and advanced radiotherapy devices

The interactions of low energy radiation with biological material exhibit complex processes, which can be modeled using Monte Carlo simulation software. With the use of a modeling package called GEANT4 that was initially developed for particle physics applications at CERN, our model includes an electron beam, the production of low energy radiation and the interaction of radiation with biological material. Using data collected from experiment, our group models the energy and spatial distribution of the generated x-rays.

Studies have shown that chemical and biological processes resulting from radiation interactions affect biological tissue in significant ways. The accumulated dose of radiation in cells can be calculated with the model. In our collaboration with the Department of Bioengineering at Clemson University we compare this data to experimental results and correlate cellular effects with received dose.

Apart from cellular level interactions our GEANT4 based model also allows the detailed study of radiotherapy devices using gamma radiation for medical treatment. Our aim in this research area is the support of development of advanced instrumentation including new treatment head designs and irradiation procedures.

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Effect of low-dose soft X-ray radiation on cells

Literature currently suggests that there are positive effects of low dose x-ray radiation on the proliferation of osteoblast cells. By testing the effects of low dose x-ray radiation on common cell types such as 3t3 fibroblasts, which aid in the repair of tissue damage, the possibility for low dose x-ray radiation to stimulate fibroblast mitosis in the presence of tissue damage could lead to effective wound repair. The purpose of this project is to investigate if low-dose soft x-ray radiation on healthy cells could yield increased proliferation without damaging the cells.

In our initial studies we have found an increasing proliferation rate for the irradiated cells. This could suggest that very low dose soft x-ray radiation benefits cells instead of harming them. Initially it appears as though the radiation either pauses the cells’ growth or kills them prior to a potential defense response that later accelerates growth. These tests further prompt the investigation for more specific responses that cause proliferation change.

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Advanced treatment head designs for radiosurgery

Stereotactic radiosurgery (SRS) is a form of external beam radiation that combines multiple finely collimated radiation beams and stereotaxy (3D target localization). The multiple radiation beams intersect to deliver a single, precise, high dose of radiation to a precisely defined location, while minimizing radiation exposure to surrounding tissues. SRS has been used to treat functional disorders of the brain such as trigeminal neuralgia or arteriovenous malformations, vascular malformations, and intracranial and extracranial benign and malignant tumors. Extracranial areas that have been treated with SRS include the abdomen, liver, lung, neck, pancreas, prostate, and spine.

Current exiting SRS technologies are based on three types of radiation sources: particle beam accelerators, electron acceleration generated photon beams, and Co-60 radioisotope based gamma beam systems. The first two accelerator based systems only deliver a single beam for each treatment head (beam delivering unit), while multi-beam gamma technologies have limitations in the numbers and angles of beam entries into patients.

In realizing the ultimate goal of maximizing dose concentration within the treated volume and minimizing radiation to surrounding normal tissue our aim is investigate different treatment head designs, beam configurations, and irradiation procedures experimentally and using Monte-Carlo modeling techniques.

For more information, please see our poster on the use of Precision Robotic Treatment Head (PRTH) for a Safer, More Effective Stereotactic Radiosurgery.

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