Enhanced Ultrasound Imaging
for Brachytherapy Assessment

Aug 12 1998. For some men diagnosed with early stage prostate cancer radioactive seed implantation is an alternative to surgical removal of the prostate gland or external-beam radiation therapy. About 10 percent to 15 percent of patients with localized prostate cancer currently are being treated with this implantation, known as brachytherapy.
     A new ultrasound imaging technology may reduce the cost and time required to find out if a patient is a candiadte for this procedure. It may also help surgeons to more accurately place the radioactive seeds according to the treatment plan, the developers say.
     "This improvement will allow physicians to make better treatment decisions and to make them immediately known to the patient," says Dr. Peter Grimm, executive director of the Seattle Prostate Institute and a pioneer in seed implantation treatment. Grimm developed the new ultrasound imaging protocol with Yongmin Kim, professor of electrical engineering at the University of Washington, and Sayan Pathak, a graduate student in bioengineering.
      Brachytherapy involves placement of radioactive seeds into the prostate gland to kill cancer cells. Guided by an external template and ultrasound imaging, the surgeon uses a needle to implant the seeds according to a pre-determined plan. To be successful, however, the surgeon must be able to pass the needle under the patient's pubic arch bone to reach all parts of the prostate gland. In 20 percent to 40 percent of cases, the pubic arch will interfere with the surgeon's needle.
      Since brachytherapy provides only one chance to place the seeds correctly, surgeons need to know whether pubic arch interference exists before they begin the procedure. To make that assessment, an ultrasound study is first done to determine the size and shape of the patient's prostate gland. If the volume of the prostate is 40 cubic centimeters or less, pubic arch interference is rarely encountered. If the prostate volume is 60 cubic centimeters or greater, interference is almost always present. In cases where the prostate volume is 40-60 cubic centimeters, the position of the pubic arch bone becomes critically important.

Reduces Ultrasound Image "Noise"
Until now, a separate X-ray computed tomography (CT) scan has been required to effectively visualize the pubic arch bone. The CT scan of the pubic arch bone is overlaid with an ultrasound image of the patient's prostate gland to determine whether a surgeon would encounter interference during the brachytherapy procedure. Conventional ultrasound technology historically has been unable to accurately detect the pubic arch bone.
      "Bone tends to scatter and weaken the ultrasound waves and create a lot of visual noise in the image," explains Kim. "We developed image enhancement technology to reduce the visual noise and significantly increase contrast in ultrasound imaging of the public arch bone."
      The new technology enables doctors to see the prostate gland and pubic arch bone in a single ultrasound image and to assess pubic arch interference within minutes of the patient scan. Ultimately, Kim says, it will be installed within the ultrasound machine itself so doctors can view the combined prostate gland-pubic arch image in real time as the patient is being scanned.

Allows Patient to Lie "Tucked"
      In addition, Grimm says, the ultrasound technology allows doctors to examine their patients in the same tucked-knee position that they will be in for the brachytherapy procedure. CT exams require patients to lie in a prone position, which changes the relationship of the pubic arch bone to the prostate and makes it more difficult to assess whether pubic arch interference will be encountered during surgery.
      In pre-clinical studies at the Seattle Prostate Institute, the new ultrasound imaging technology accurately predicted whether pubic arch interference was present in all but two of 307 planned needle insertion points. This is well within clinically accepted limits, Kim says. "The CT essentially offers an expensive and time-consuming guess. Obviously, as a doctor, I want to reduce guesswork as much as possible," Grimm says. "The obvious advantage of the ultrasound protocol is that it accurately reproduces the anatomical situation that the surgeon will encounter in the operating room. This gives surgeons better information and improves the quality of care they can provide."

A paper describing this research has been accepted for publication in the journal IEEE Transactions on Medical Imaging.

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Aug 12 1998, modified December 26, 1998

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