Safer, More Accurate Radiation Therapy for Expecting Mothers
Video of X. George Xu, professor of nuclear and
Photo Credit: Rensselaer Polytechnic Institute
New modeling tools enable more effective cancer
treatment and imaging procedures
Troy, N.Y. — 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 Polytechnic Institute 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,” said X. George Xu, professor of nuclear and biomedical
engineering at Rensselaer, 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
radiation imaging and treatment for pregnant women,” Xu said.
“The tools we have developed for this research should also open
up several new avenues for improving the field of radiation
|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.
Photo Credit: Rensselaer Polytechnic Institute
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
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 said. 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:
three months, six months, and nine months. 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 existence
of such scans was publicized, and Xu contacted the physician to
obtain copies of the scans.
Xu said BREP turned out to be extremely effective for
modeling the complex topology of human organs, and he expects
the practice to catch on.
“We are convinced that it would have been impossible to
develop such a complete, consistent, and anatomically realistic
set of models from medical images that are hard to come by,” Xu
said. “It is clear that the current trend will continue to
involve BREP type of modeling.”
The research project, funded by the National Cancer
Institute, was presented in the article “A
boundary-representation method for designing whole-body
dosimetry models: pregnant females at the ends of three
gestational periods — RPI-P3, -P6, and -P9,” published in the
most recent issue of the journal Physics in Medicine and
With the models complete, Xu and his team will share their
data with other researchers investigating the same topic. Xu
said it will likely be about one year before the models are
verified and accepted by the medical community, and then
integrated into computer software as a new standard for
determining and administering radiation therapy to expecting
Co-authors on the paper include Rensselaer nuclear
engineering and engineering physics graduate student Juying
Zhang, and postdoctoral research associate Valery Tarenenko.
Chengyu Shi, of the Cancer Therapy and Research Center in San
Antonio, Texas, is also listed as a co-author.
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
Contact: Michael Mullaney
Phone: (518) 276-6161