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.
A new approach
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.
Pregnancy concerns
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."
Copyright (c) 2008, Albany Times Union, N.Y.
