Computer simulations used for radiotherapy treatment planning rely on sophisticated virtual human-body models, or phantoms. Existing models of pregnant females have been created using constructive solid geometry (CSG) tools, which are based on simple shapes such as spheres, cones and cylinders, connected to create a larger structure. Such conventional methods of phantom creation, however, cannot account for the rapid changes of a pregnant woman's internal physiology as her organs shift to accommodate the growing foetus.

Instead of CSG, the Rensselaer team employed boundary representation (BREP) software - a more flexible tool that's used in the entertainment industry to create computer-animated models for movies and video games. BREP features a more robust toolbox for manipulating the surface of model components and is highly effective for creating medical phantoms consisting of complex organs.

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

Xu and his team used the BREP tools to create 3D 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 foetus organ by organ, relying on computer-generated mesh models. They also supplanted the model with data from rare CT scan images of a pregnant patient, taken when the pregnancy was unknown.

"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," said Xu. "The tools we have developed for this research should also open up several new avenues for improving the field of radiation dosimetry."

With the models complete, Xu and his team plan to share their data with other researchers investigating the same topic. Xu says it will likely be about one year before the models are verified and accepted by the medical community. At that stage, they could be integrated into computer software as a standard tool for planning and administering radiation therapy to expectant mothers.

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