High-Tech Seed Placement Making Brachytherapy Even More Precise
Brachytherapy - implanting radioactive seeds into the prostate to kill cancer - has come along way since the 1970s, when doctors made an incision in the prostate and tried to space the seeds evenly, with a "free-hand" approach. Over the last decade, with the use of CT scans and ultrasound guidance to place the seeds through the perineum, and the development of dosimetry - precise placement of the seeds to kill prostate tissue, but avoid harming nearby organs, such as the bladder and rectum - brachytherapy has become much more effective. This is particularly true as more men, with the help of regular PSA screening, are diagnosed with early-stage prostate cancer, where the cancer is still confined within the prostate. However, the goal is perfection - curing prostate cancer with minimal side effects -and as good as brachytherapy has become, radiation oncologists and colleagues at Hopkins are working to improve it. One challenge is that there is no "regulation"prostate - no standard in size, shape, or tissue consistency. Every man's prostate is different. This means that "the highest level of precision is sometimes difficult to achieve,even for the most experienced physicians,"says Danny Y. Song, M.D., assistant professor of radiation oncology. Sometimes, for example, dense prostate tissue slightly bends the needles used to place the seeds, and the implanted seeds don't always end up exactly where they are supposed to be. "In addition, although we use ultrasound to view the prostate during the procedure, seeds cannot readily be seen on the ultrasound image once they have been placed. This means that the results of the implant are not always exactly what was intended - and yet, when it occurs, this cannot always be identified and corrected in the operating room. "
Treating a moving target
Even with "pre-plan" (a map and radiation dosage guide drawn up before the procedure) and intraoperative "real time" dosimetry, "the treatment plans are based on a fixed organ," says Chan. "In reality, the prostate gland is mobile. As it is pierced with needles, the prostate gland can move, rotate, and swell. The radioactive seeds can also move, shift and migrate during the procedure. This can make perfect implants difficult." (This frustrating movement of the prostate, by the way, can also happen during a needle biopsy to look for cancer, and is why doctors now take a dozen samples instead of just a handful.) What's needed, continues Chan, is "a better mouse trap" - improved dosimetry. "We are currently evaluating two different approaches to help solve this issue." One potential solution involves Dan Stoianovici, Ph.D., Director of Uro-Robotics Laboratory at the Brady Urological Institute. Stoianovici
|What does this mean? The ability to see in the dark, to know what's happening to the ever-changing prostate during the procedure.|
has been developing an automated method of performing brachytherapy, using a computer-driven, robotically automated brachytherapy seed implant device, which can be coupled with continuous real-time MRI imaging. Another benefit: "The automatic implant device will make the success of treatment independent from the operator," says Chan. "Dr. Stoianovici's work is revolutionary, and will change the face of prostate brachytherapy.
Another approach involves a device created by Gabor Fichtinger, Ph.D., and colleagues in the Hopkins School of Engineering. "This device links an x-ray machine, which is capable of viewing the seeds but not the prostate, to an ultrasound, which can view the prostate but not the seeds," says Song. Computer software then spots the seeds onthe x-ray and projects their location onto the ultrasound, showing exactly where the seeds are. What does this mean? The ability to see in the dark - to know what's happening to the ever-changing prostate during the procedure. "The concept," explains Chan, "is that as the seeds are placed, the prostate gland is constantly reimaged and revaluated for adequate dosimetry. If a seed shifts, a coldspot' would be recognized and treated. This is not possible with current techniques."The result: "An ideal seed distribution," says Song.
The next step is to prove that these "better mousetraps" work as well as the Hopkins scientists expect. "We have recently been awarded funding through the Prostate Cancer Research Program of the Department of Defense to carry this out this study," says Song. He and colleagues will conduct a randomized study, comparing men treated with standard brachytherapy techniques to men treated with the new technology. If shown to be effective, this technology will rapidly be made available to all physicians, and their patients, who are using brachytherapy to treat prostate cancer.