A trio of innovations to treat prostate CA is being touted by the University of Wisconsin-Madison:
Directionally emitting radioactive sources, a device for placing needles and seeds, and a super-fast treatment-planning method were developed by UW-Madison engineering physics professor Douglass Henderson and medical physics associate professor Bruce Thomadsen.
To eradicate diseased tissue, physicians implant up to 100 radioactive seeds in the prostate. Like a tiny grain of rice, each seed is cylindrically shaped and emits radiation in all directions-increasing its likelihood of zapping healthy tissue, too.
So, borrowing a concept from nuclear materials handling, Henderson and Thomadsen designed directional seeds-sources with vertical shielding along one side. “I think nobody’s done it before because they look at these sources, which are only eight-tenths of a millimeter in outer diameter, and they say there isn’t enough space to put shielding,” says Thomadsen. “We found you can compress things and you can do it.”
As a result, they can implant seeds, particularly at the boundaries between healthy and diseased tissue, that steer radiation where it’s needed most.
With graduate student Liong Lin, the two developed prototypes and conducted successful radiation simulations. Now they are working with a leading brachytherapy products company to develop experimental prototypes. To keep the seeds from rotating once they’re implanted, the group also hopes to modify their design to incorporate a wedge-shaped anchor along one vertical side.
Implanting the seeds accurately is no small feat. With a hole-studded grid mounted over the patient as a guide, physicians use a hollow needle to insert the seeds manually. They rely on real-time ultrasound images of the prostate to ensure proper seed location and depth. But both the confines of the grid and the ultrasound itself limit the process, meaning that the radioactive seeds may not make it to the correct locations, says Thomadsen. So he and his graduate students abandoned the grid and built a robot that could deliver seeds more precisely than a physician could by hand.
Graduate student Michael Meltsner built a prototype robot and has perfected it by programming it to implant seeds into oranges. “It’s a really basic prototype, and he’s at the point where we have to test to make sure that, in the simple form we have, it’s going to perform exactly how we want,” says Thomadsen.
By next year, when the system is complete, it will provide countless angles for inserting seeds and will enable physicians to properly orient seeds that contain shielding.
To plan the seed placement for maximum effectiveness, physicians currently map an ultrasound view of the prostate on a 3-D grid, use optimization software to calculate several sets of possible seed locations, and determine which configuration will work best. But current optimization methods are iterative methods-that is, they calculate a solution, make a change, calculate a new solution, make a change, and so on.
Inspired by a reactor physics technique called adjoint, or “backward” transport, Henderson, Thomadsen and their graduate students developed a method that could reduce the time of this treatment-planning step from as long as 40 minutes to just a few seconds. “The adjoint function plays a big role in the selection of the seed position,” says Henderson.
The press release…