**ORISE Cytogenetic Biodosimetry Laboratory:**

**A National Resource**

Voiceover:

Mass casualties. Overburdened emergency response systems. Spreading
contamination. 

As the threat of nuclear terror attacks becomes more credible, a serious
gap exists in the United States' ability to respond effectively. A
radiological event could expose civilians to dangerous levels of
ionizing radiation; however cytogenetic biodosimetry can be used as a
proven technique for calculating human radiation exposure during such an
event.

The Oak Ridge Institute for Science and Education in Oak Ridge,
Tennessee, operates a federally funded facility---the Cytogenetic
Biodosimetry Laboratory---that can perform this clinical analysis.
Cytogenetic Biodosimetry identifies damage to chromosomes in individuals
who have been exposed to ionizing radiation. It is the most accurate way
to determine the absorbed dose, which is critical for physicians
managing patients' radiological treatment.

Dr. Livingston:

"One of the cardinal principles of radiation biology is the fact that
the sensitive site within the cell is actually the DNA molecules within
the nucleus of the cell. So if we have an efficient method to measure
DNA damage within the cell, we can get an estimate of the dose, which
has been absorbed by the person. Since the chromosomes within the
nucleus of the cell are the repository of the DNA molecules, we can
study the DNA damage by looking directly at the chromosomes themselves."

Voiceover:

The cytogenetic biodosimetry process begins with acquiring a blood
sample for analysis. ORISE can receive the sample at room temperature
from any physician's office, hospital or laboratory around the world as
long as it is received within 24 hours.

Once the blood sample is received at the laboratory, it is unpacked,
inspected, and quickly set up in culture. White blood cells are cultured
under sterile conditions in an incubator using a standard growth medium
for 48 hours.

Dr. Livingston:

"One of the disadvantages of the test is that it does take a fair amount
of labor, and it takes a three-day period of time in order to come up
with the answer. So it's not a quick and easy test, but it is considered
the gold standard for biological dosimetry, and it has been proven
through the years to be a successful way of estimating the dose with the
defined levels of probability."

Voiceover:

Next, culture tubes are centrifuged and cells are re-suspended in a weak
salt solution. This allows the chromosomes to separate and spread evenly
on slides. The chromosomes are then cleaned and allowed to dry in a
controlled environment.

Human chromosomes are very small, typically 2 to 10 microns in length,
so it is necessary to stain them to enable magnification of up to 1,000
times to examine their structure under a microscope. Once stained, the
slides are each mounted with a thin glass cover slip and taken to the
cytogenetics workstation. Here microscopic analysis of large numbers of
cells are screened for those specific types of chromosomes that reflect
radiation damage.

Dr. Livingston:

"...when we talk about the field of cytogenetic biodosimetry, what we
are doing is analyzing the chromosomes, which are the biomarkers of the
damage that is sustained. When ionizing radiation passes through the
nucleus of the cell, it induces what are called double strand DNA
breaks. If those breaks are not repaired properly it can lead to an
exchange type chromosome aberration and form what is called a dicentric
chromosome or a chromosome with two or more centromeres on it. As it
turns out the dicentric chromosome frequency is a sensitive index of the
amount of radiation that is passed through the nucleus of the cell. So
in cytogenetic biodosimetry, we're primarily concerned with the
measurement of those dicentric chromosomes."

Voiceover:

Dicentric chromosomes are located using an automated workstation
consisting of a highly sophisticated microscope coupled with a slide
changer. The microscope can automatically process as many as 80 slides
unattended overnight. Each slide, which can hold up to 1,500 dividing
blood cells, takes only six minutes to process. The microscope's
software can create a karyotype table, which allows researchers to
quickly identify chromosome abnormalities. The frequency of dicentric
chromosomes is then compared to a dose response calibration curve to
identify the type of radiation a patient has been exposed to, as well as
his or her estimated dose.

Only the Armed Forces Radiobiology Research Institute in Bethesda, Md.,
can provide a similar service in the United States, however, its
resources are dedicated to military applications of the technology.

The ORISE lab also participates in an international biodosimetry network
along with four other laboratories. Researchers continue to develop
methods to improve the accuracy and speed of cytogenetic analytical
methods.