Researchers use one-of-a-kind device that bombards cells with energized electrons
In our high-tech world, everyone is exposed to low dose radiation in one form or another. It comes from CT scans and X-rays used in medical tests, naturally occurring radon gas, common household items such as smoke detectors and televisions and from cosmic rays that we’re exposed to in the upper atmosphere when we fly on airplanes. Is exposure to low levels of radiation harmful to your health? Or, could it actually be good for you, as some scientists believe?
With funding from the U.S. Department of Energy’s Low Dose Radiation Research Program, researchers at the University of Maryland School of Medicine are starting a three-year study to examine the effects of low dose radiation on human cells. Using a specially built irradiation device called an electron microbeam, they are able to bombard single cells or groups of cells with energetic electrons that mimic those produced by x-rays or gamma rays. The one-of-a-kind microbeam was developed by scientists at the Pacific Northwest National Laboratory in Richland, Wash., and recently relocated to the University of Maryland.
“We live in a radiation environment,” says William F. Morgan, Ph.D., the principal investigator and professor of radiation oncology and director of the radiation oncology research laboratory at the University of Maryland School of Medicine. “We are constantly being exposed to low levels of radiation. The question is whether this radiation is good or bad. Is there a point below which there are no harmful genetic effects? This study is a first step in our quest to find answers to these important questions.”
Dr. Morgan says that while the harmful effects of high doses of radiation on humans are well-documented, there is considerable debate among researchers about the impact of low dose exposure, especially over long periods of time. “Some scientists believe that all exposure to radiation has some genetic risk. Others believe that a little bit of radiation is good for people, helping them to adapt to our environment. And there is some good evidence to support that. At this point, nobody knows for sure,” he says.
The electron microbeam was developed by Marianne Sowa, Ph.D., and Greg Kimmel, Ph.D., senior research scientists at the Pacific Northwest National Laboratory, with support from the U.S. Department of Energy. Dr. Sowa is also an adjunct professor of radiation oncology at the University of Maryland School of Medicine and a co-principal investigator on the study.
Drs. Morgan and Sowa are looking at the effects of low LET (linear energy transfer) radiation on human cells, which are grown in a laboratory. This is the same type of radiation produced by gamma or x-ray sources. Specifically, their research focuses on what is known as the “bystander effect.” Cells directly exposed to radiation appear to “communicate” with neighboring cells, which in turn respond as if they also have been irradiated, according to Dr. Morgan. This communication can occur in two ways – passing molecules through adjoining membranes or releasing factors into the bloodstream that can affect other cells, he says.
William F. Regine, M.D., professor and chairman of the Department of Radiation Oncology at the University of Maryland School of Medicine, says, “This research has very important implications since many people are exposed to low dose radiation from a variety of sources. We are very pleased that the Department of Energy has recognized the strength of our radiobiology program by selecting us to conduct this study.”
Dr. Sowa says that it took more than three years to develop the electron microbeam. Unlike other microbeams, it does not use a linear accelerator to produce particles and is therefore less bulky and more portable. It can also target individual cells, or a subset of cells, allowing researchers to examine not only the effect on cells directly hit by radiation but also the potential impact on nearby cells. “This microbeam is a very simple, but unique, device,” Dr. Sowa says. “No one else has a true low LET electron microbeam to conduct this kind of cutting-edge research.”
The microbeam incorporates a pulsed electron gun, a microscope and a “collimator” to help provide a spatially resolved, or defined, electron beam. The cells are grown on special dishes with a Mylar bottom similar to stretched plastic wrap. Researchers use a fluorescent microscope and a highly sensitive GFP (green fluorescent protein) assay to detect even subtle changes in the cells.
“When radiation deposits energy into a cell, it kicks out electrons that can cause genetic damage,” Dr. Morgan explains. “By focusing on these electrons, we hope to be able to trace the biological response—not only in the irradiated cells but also in neighboring cells. We also want to see if there are delayed effects, with damage showing up in later generations of the targeted cells.
“Ultimately, we want to learn whether these genetic changes signal an increased risk of cancer. Currently, we don’t have a reliable indicator of risk,” Dr. Morgan says.
The U.S. Department of Energy’s Low Dose Radiation Research Program was created to help determine health risks from exposure to low-level radiation. Regulatory agencies will use results of this and other studies to evaluate models that predict health risks from low dose radiation and to determine whether current radiation protection standards reflect the most recent scientific data.
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