ALBANY, N.Y. -- Destroying a tumor in a body with radiation poses
a number of challenges and risks, especially for a pregnant woman
and her fetus.
Researchers at Rensselaer Polytechnic Institute are working to
reduce those risks by advancing computer techniques that use
virtual models of the human body. Their latest research looks at
ways to protect a developing fetus.
Their goal is to help hospitals and radiologists more accurately
calculate required dosages to destroy a tumor, while minimizing or
eliminating the risk of damage to nearby cells and organs.
The work at RPI adds to similar research worldwide. About 30
other virtual models have already been created for a variety of
body types. Some of the earliest models consisted of simple
geometric shapes -- cones and cylinders, and internal organs that
looked more like pieces of a puzzle.
The latest models are far more realistic.
Researchers at RPI and elsewhere use magnetic resonance imaging,
computerized axial tomography -- or CAT -- scans, and even photos of
cadavers to supply the thousands of data points required to build
their models.
The scientists are also defining the different organs and
tissues, because the radiation affects them differently.
So far, researchers, led by X. George Xu, have prepared what
they call a Visible Photographic -- or VIP -- man, a
three-dimensional virtual human that can be used to simulate how
radiation treatments affect human organs and tissues.
They've added a fourth dimension -- time -- that takes into
account the movement of the tumor and body tissues as the patient
breathes over time.
For their pregnancy research, the scientists were able to get
the necessary data points to construct a computer model from CAT
scans taken of an unidentified woman in an upstate New York
hospital in the early 1990s. At the time, neither the woman nor her
doctor knew she was pregnant; otherwise, the images wouldn't have
been taken because of the radiation risks CAT scans present to a
fetus.
But the images, while helpful, were of one point in time. To
model how the body and the fetus change with time, Xu and his team
of researchers decided to use a tool from the manufacturing and
computer gaming industries.
"Pregnant females are even more difficult to model using
current methods, so we took an entirely new approach," Xu said.
The tool -- boundary representation, or BREP, method -- uses
three-dimensional surface modeling technologies instead of the
voxels (three-dimensional pixels) used in the more primitive
approach to model building by computer.
"We adopted this BREP approach to define three-dimensional
organs," Xu said. "Particularly, we figured out how to change the
shape and size of the fetus in order to create realistic
pregnancies for different gestational periods."
The researchers then model how the radiation would scatter
through the body as it passes through bones and other tissue.
"Radiation treatment of patients needs to reduce secondary
radiation to healthy tissues near and away from the tumor," Xu
said. "Radiation-treated cancer survivors are known to exhibit a
higher risk of developing what is called 'second cancers.'
Traditionally, radiation doses outside the 'treatment volume'
defined for the tumor are not accurately accounted for."
Xu will share his data with other medical researchers, who
likely will incorporate them into existing models used to calculate
proper dosages for a variety of tumors.
"It's really quite theoretical," said Priscilla Butler, senior
director of the American College of Radiology's Department of
Quality and Safety.
Physicians remain hesitant, however, to use radiation to treat
tumors in pregnant women. An estimated one in 3,000 pregnant women
has breast cancer, according to a spokesman for the American Cancer
Society.
"A breast is not that far away" from the fetus, said Dr. Susan
Gibbons of Albany Medical Center. "And that's a concern."
She said the tool would be unlikely to change clinical practices
anytime soon.
"We're going to err on the side of caution, especially where
there's another alternative," she said. "With breast cancer, a
patient can have a mastectomy."
But Xu hopes his research eventually will provide doctors with
another tool.
"Our work is attempting to remove the unknown variables
involved with using radiation therapy on expecting mothers," said
Xu. "We hope that someday soon, our models will allow for better
radiation shielding for the fetus, and women will have an option
that is nearly as safe yet much less disruptive than a
mastectomy."
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(E-mail: eanderson@timesunion.com.)
c.2008 Albany Times Union