Inside Rensselaer
* Safer, More Accurate Radiation Therapy for  Expecting Mothers
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Researchers at Rensselaer have developed new modeling tools that will enable more effective cancer treatment and imaging procedures for pregnant women. These finalized models, from left to right, represent a woman who is six months and nine months pregnant. The models were plotted with the design program Rhinoceros.
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Safer, More Accurate Radiation Therapy for  Expecting Mothers
Developing fetuses are extremely sensitive to radiation, which poses an impossible dilemma for expecting mothers in need of screening or treatment for cancer. Now researchers from Rensselaer have developed a new set of modeling tools that could enable safer, more accurate, and more effective radiation therapy and nuclear medicine imaging procedures for pregnant women.

Radiation is a doubled-edged sword: It holds the power to cure cancer, but if used improperly it can also cause serious damage to the human body. The situation is even more critical with pregnant females, as any errant radiation could severely harm and impede the growth of the fetus.

“The human body is a particular challenge to model because of its wide variety of organs, each with a complex and unique shape,” says X. George Xu, professor of nuclear and biomedical engineering, who is leading the project. “Pregnant females are even more difficult to model using current methods, so we took an entirely new approach.”

Physicians use advanced computer simulations to determine the correct dose of radiation to administer to patients. These computer simulations are based on sophisticated virtual models of the human body. About 30 of these models, sometimes called “phantoms,” have been developed worldwide.

The data needed to build such models, however, requires extensive X-rays and computed tomography scans. Since pregnant patients are prohibited from undergoing X-rays or other imaging procedures, there has never been enough data to create an accurate phantom of a pregnant woman.

“These new models should be extremely useful for understanding the risks of radiation, and for better planning of radiation imaging and treatment for pregnant women,” Xu says. “The tools we have developed for this research should also open up several new avenues for improving the field of radiation dosimetry.”

X. George Xu
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X. George Xu

Conventional methods of phantom creation simply cannot account for the rapid changes of a pregnant woman’s internal physiology as her organs shift to accommodate the growing fetus. So instead of employing the conventional constructive solid geometry (CSG) tools to construct the computer model, Xu and his team turned to boundary representations (BREP) tools.

CSG models are based on building and connecting simple shapes such as spheres, cones, and cylinders to create a larger structure. BREP is more flexible and features a more robust toolbox for manipulating the surface of model components. BREP is widely used in the manufacturing industry for computer-aided design, and in the entertainment industry to create computer-animated models for movies and video games, Xu says. As it turns out, BREP software is also highly effective for creating medical phantoms consisting of complex organs.

Using this new set of tools, Xu and his team created three 3-D models of pregnant females at various gestational stages. The team built the models of the expecting mother and fetus organ by organ, relying on computer-generated mesh models, as well as supplanting the model with data from rare CT scan images of a pregnant patient. The images were taken around 2004 in an upstate New York hospital, in a situation where both the woman and her physician were unaware she was pregnant.

The research project, funded by the National Cancer Institute, was published in the Dec. 7, 2007 issue of the journal Physics in Medicine and Biology. Co-authors on the paper include Rensselaer nuclear engineering and engineering physics graduate student Juying Zhang, and postdoctoral research associate Valery Taranenko. Chengyu Shi, of the Cancer Therapy and Research Center in San Antonio, Texas, is also listed as a co-author.

George Xu has led the creation of several different phantoms. For more information on his work, visit the Rensselaer Radiation Measurement & Dosimetry Group at http://RRMDG.rpi.edu.

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Inside Rensselaer
Volume 2, Number 1, January 17, 2008
©2008 Rensselaer Polytechnic Institute
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