Radiobiology Program Breaks New Scientific Ground at 88-Inch Cyclotron

January 24, 1996

By Jeffery Kahn, JBKahn@LBL.gov

Sometimes what goes around comes around. Prior to the existence of the Bevalac biomedical facilities, biologists at Berkeley Lab used three other accelerators as a source of charged particles for their investigations: the 88-Inch Cyclotron, the 184-Inch Cyclotron and the SuperHILAC. Their basic studies and the subsequent Bevalac program led to improvements in cancer therapy that are now used worldwide. They also provided insight into the mechanisms used by cells in cell division and DNA repair.

When the Bevalac shut down four years ago, Eleanor Blakely and Aloke Chatterjee of the Life Sciences Division's Department of Radiation Biology and DNA Repair approached the Nuclear Science Division and the 88-Inch Cyclotron operations group. Seeking an onsite facility to continue their work, they asked if it would be possible to create a new beamline suitable for radiobiology. In response, former NSD Director James Symons and Cyclotron head Claude Lyneis agreed to help support Life Sciences' ongoing research program.

Within a year of the initial request, a new radiobiology experimental program debuted at the 88-Inch. The focus of this program is to delineate the biological effects of low energy particles. These particles deposit a great deal of energy as they slow down. The ability of cells to tolerate such exposures is dependent upon the endpoint studied and the type of cell exposed. Particles produced by the cyclotron that are important for these investigations include alpha particles that simulate radon exposures, heavier charged particles and protons that are found in the space radiation environment, and protons and helium ions that are used in cancer therapy. In concert with the quantitative studies, the goal of the investigations is to determine which biological processes influence the nature of the biological response.

Though radiobiology accounts for less than five percent of the beam time at the 88-Inch, the request for a suitable beam line was not a minor one. The 88-Inch Cyclotron has been principally dedicated to nuclear physics since it generated its first beam in 1961. Beams that are designed to break apart an atomic nucleus are very different from those targeted at a substantially larger biological sample. And a customized beam line was just the beginning of what was required to adapt the facility for radiobiology experiments.

Berkeley Lab researchers have used the new facility at the 88-Inch to explore topics including the nature of chromatin structure, DNA damage and repair following simulated radon exposure, genetic constraints on the occurrence of mutations, and the biological basis of radiation-induced cataract formation.

Speaking for this research community, Life Sciences Division scientist Amy Kronenberg says a large, collective effort made possible the 88-Inch radiobiology program.

"People from four divisions worked together to make this happen," said Kronenberg. "Members of the Nuclear Science, Engineering, EH&S and Life Sciences divisions combined to design a beam line that would accommodate the needs of Life Sciences researchers." This beam line also has proven useful for other applications.

Learning process

Building and tuning a life sciences beamline involved a learning process. The beams used in the study of the atomic nucleus are typically 1-2 centimeters in diameter. A much broader beam, 10 centimeters in diameter, is required for radiobiology experiments. Broadening the beam would be relatively simple except for the requirement that its intensity be uniform, that is, equal whether at the middle or at the edge of the beam. Don Syversrud and Doug Garfield led the mechanical engineering effort required to create a beam that has 95 percent uniformity across its breadth.

The operations staff at the 88-Inch played a crucial role in the development of beam optics and uniformity for the new beamline and is intimately involved in beam delivery. The biology runs are unusual in that investigators use different types of particles within a few hours of one another. This is different than a typical nuclear physics run, and the biology runs require constant activity on the part of the operations staff. On duty around-the-clock, this team is headed by Aran Guy and includes Reba Siero, Tom Gimpel, Bob Coates, Vicki Sailing, Jim Morel and Ed Diaz.

Radiobiologists cannot do research at an accelerator unless they can measure the radiation dose that the beam delivers to the biological sample. Over decades, very precise dosimetry systems were developed for the Bevalac facility. Physical equipment and expertise critical for dosimetry for biological experiments were transferred from the Bevalac to the 88-Inch by a team that included Peggy McMahan, Bill Holley, Bernhard Ludewigt, Cary Zeitlin, and Lawrence Heilbronn.

To control the dosage, a Macintosh-based system was developed by McMahan, Roger Dwinell, and several visiting engineers to allow biologists to control the beam and to document the dose level and uniformity delivered to each sample. This capability is very important, especially since exposures are often brief and accuracy is crucial.

New safety issues

Radiobiology research poses a new set of environment, health, and safety issues at the 88-Inch. Unlike typical experiments run by nuclear scientists, life scientists go in and out of the experimental caves to change experimental samples repeatedly throughout the course of a run. As a result, new procedures and controls have been set up to guarantee safety. Occasionally, an experiment requires that the samples be labeled with radioisotopes. The EH&S team that oversees the coming and going of these samples includes Ruth Mary Larimer, Roger Kloepping, Glenn Garabedian, and Jim Hayes.

Speaking for a very grateful group of biologists, Kronenberg said that the efforts of this diverse and talented group of individuals helped ensure the continuation of accelerator-based radiobiology onsite at Berkeley Lab.

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Radiobiology Beam at 88-Inch Cyclotron Producing Wealth of New Science

Life scientists have capitalized on the radiobiology beam line at the 88-Inch Cyclotron, conducting a number of experiments. To date, they include the following.

• LSD's Bjorn Rydberg has made a discovery that challenges what had been the prevailing theory of how DNA is organized within the cell nucleus. It is well known that DNA is not simply crammed into the nucleus but is structured with specific nuclear proteins into a precisely packaged structure. This combination of DNA and specialized proteins creates a dense, compact fiber called chromatin.

  To probe the structure of chromatin, Rydberg used ionizing particles from the cyclotron to create fragments of chromatin. As predicted four years ago by Life Sciences Deputy Head Aloke Chatterjee and his colleague William Holley, the size distribution of the chromatin fragments provides a signature of the structure. These experiments have challenged the previously accepted model of chromatin structure and support the so-called "Zig-Zag model."

• In an ongoing collaboration with Professor Charles Waldren, Dr. Akiko Ueno, and graduate student Susan Kraemer from Colorado State University, Amy Kronenberg's group has determined that very large deletions and chromosomal translocations can be caused by energetic protons and nitrogen ions. Using a series of different cells with different chromosomal targets for mutation, they showed that the number of mutations detected was highly dependent on the location of essential genes on a particular chromosome. Ongoing experiments seek to measure the frequency of whole chromosome loss using new model systems. The loss of whole chromosomes can be a major factor involved in both birth defects and cancer. This research effort is part of the NASA Specialized Center of Research and Training that involves LSD's Department of Radiation Biology and DNA Repair and the Department of Radiological Health Sciences at Colorado State University. Kronenberg's group is also investigating the role of programmed cell death and DNA repair in susceptibility to mutation.

• LSD's Priscilla Cooper is directing a research effort in which the cyclotron is used to produce alpha particles that simulate those emitted by radon. Radon, a radioactive gas, is the dominant source of natural background radiation. The high intensity of the cyclotron beam and exact control of the alpha particle energy make possible experiments that are virtually impossible to perform with radon gas itself.

  Cooper has discovered that base damage in DMA induced by alpha particles is repaired more slowly than base damage caused by x-rays. She hypothesizes that the clusters of damage caused by alpha particles are more difficult for DNA repair enzymes to correct than the isolated damages caused by x-rays.

  Former postdoctoral fellow Markus Lobrich, who recently returned to Germany after completing his fellowship in the Cooper lab, has accomplished an elegant experimental proof of a long-held theory concerning DNA double-strand break production and rejoining. The theory suggests that incorrectly rejoined double-strand breaks may be an important mechanism by which mutations occur.

• LSD's Eleanor Blakely and her group are using particle radiations as a tool to explore the basic biology underlying cataract formation. Blakely is studying changes in differentiating human lens epithelial cells in tissue culture, looking at chromatin damage and modifications in protein expression that lead to the opacification of the lens.

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