Contrast-enhanced ultrasound can improve prostate cancer detection and limit the number of biopsy sites for patients, according to Dr. Ethan Halpern from Thomas Jefferson University (TJU) in Philadelphia. These gains come, however, with higher false-positive rates.
"Even with contrast-enhanced ultrasound, we cannot distinguish true-positive enhancement that is related to cancer from false-positive enhancement that is related to prostatic hyperplasia or prostatitis," said Halpern, a professor of radiology and urology.
Halpern discussed the use of contrast imaging for prostate cancer detection at the 2003 Leading Edge in Diagnostic Ultrasound conference in Philadelphia.
Traditional ultrasound has not performed well for the detection of prostate cancer. In a TJU study examining 500 patients who presented for ultrasound-guided biopsy in 1998-1999, gray-scale studies had a sensitivity of 44.1% for detection of prostate cancer, while Doppler exams were only 27% sensitive.
"This is the problem," he said. "I can show you beautiful pictures of cases where it works, but when you go to the population in general, it’s just not working well."
The techniques performed better, however, in the selection of biopsy sites. Looking only at patients with prostate cancer, gray-scale US produced an odds ratio of 1.9 in predicting cancer sites, while Doppler had an odds ratio of 3.7. Odds ratios greater than one are statistically significant.
In the U.S. today, most prostate ultrasound studies are performed to guide biopsies. The optimal number and location of biopsy cores remain a controversial topic, however.
Applying intermittent imaging techniques -- using a reduced frame rate to lower the energy deposition into tissue -- can improve the performance of ultrasound contrast agents in this application.
TJU is in the final stages of patient enrollment for a U.S. Department of Defense-funded research protocol that will evaluate the use of intermittent imaging with contrast-enhanced ultrasound of the prostate. The study, which began in August 2001, aims to evaluate 300 patients with contrast-enhanced harmonic gray scale, color Doppler, and power Doppler ultrasound. Patient recruitment is expected to be completed by early 2004.
Contrast-enhanced targeted biopsies were performed first, with up to four cores in an area determined to be enhanced maximally in the prostate. Patients then received targeted sextant biopsy, with areas of maximum enhancement within each sextant being biopsied. Each biopsy site was rated for enhancement.
"What we found is that with the targeted sextant there are areas of enhancement that we go for, and the contrast-enhanced imaging can not distinguish patients with prostate cancer with patients who have benign disease, because benign disease also enhances," he said.
However, in preliminary findings from the 265 patients already enrolled, contrast-enhanced targeted biopsy yielded positive biopsies in 124/753 cores (16.5%), compared with 128/1204 cores (10.6%) for targeted sextant biopsy.
"Thus, contrast-enhanced imaging improves the rate of positive biopsy cores by 50%," he said. "We’re clearly doing a better job of detecting cancers with contrast-enhanced targeted biopsy."
In some interesting sub-analysis of the data, 40% of positive sextant cores came from the prostate’s apex, while 18% of positive targeted cores were from the apex, Halpern said. All 10 of the cases found on sextant biopsy but missed on targeted biopsies were from the apex. Only 20% of targeted cores are going to the apex of the gland, however.
"The best biopsy (technique) may be a combination where you force yourself to target some points of the apex, and then, for the rest of the gland, we just target areas of maximum enhancement," he said.
Preliminary results from this research study will be presented in two abstracts at next month’s RSNA meeting, Halpern said.
TJU also submitted some new ideas for reducing false-positives from contrast-enhanced prostate imaging in a grant proposal to the National Institutes of Health (NIH), Halpern told AuntMinnie.com in an e-mail.
"The idea is to use drug therapy that might decrease blood flow in areas that have increased flow with normal vessels (such as areas of prostatitis or BPH)," he said. "Microvessels that are related to cancer (neovessels) should not respond to this therapy."
These ideas are still undergoing preliminary testing, however, Halpern said.By Erik L. Ridley
AuntMinnie.com staff writer
October 24, 2003
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