CT Being Tested to Detect Breast Cancer Earlier
Newswise — About 190 women are being enrolled in a clinical trial to see if computed tomography (CT) can detect breast cancer earlier, and with less discomfort, than standard mammography.
Researchers have built a prototype CT scanner for breast imaging that takes 300 sectional X-ray images through the breast. These are assembled into a single, three-dimensional composite picture that provides a clearer view through all tissues of the breast than is possible with conventional mammography, which takes two X-ray images from two vantage points.
"It's the difference between taking a picture of a crowd from across the street, versus circling the crowd and shooting hundreds of separate photos along the way, each photo only two or three people deep," said John Boone, Ph.D., professor of radiology and biomedical engineering at the University of California, Davis. "Your chances of finding a particular person in the crowd are going to be a lot better with more photos."
With CT, it may be possible to detect tumors about 5 millimeters across, about the size of a garden pea and less than half of the diameter of malignancies that generally show up in standard mammograms, said Boone, who presented preliminary results at a recent meeting of the Radiological Society of North America.
"The earlier and smaller a cancer is when it is detected, the less the chance that it has spread to the lymph nodes, lungs or bones, and the greater the chance for a permanent cure and for breast preservation," said Lydia Howell, professor of pathology at UC Davis and a volunteer in early testing of the CT scanner.
In addition to its improved accuracy, the CT scan does not require breast compression between two plates, as does mammography. Instead, the patient lies face down on a padded table that has a circular opening through which the patient places one breast at a time. A revolving X-ray CT scanner under the table takes about 17 seconds to image each breast.
"There was no discomfort," Howell said.
In the 1970s, CT was considered as a possible screening method for breast cancer, but physicians thought at the time that it would expose patients to too much radiation. CT is routinely used to image the brain, lungs, abdomen and pelvis.
Boone and his colleagues revisited the issue and discovered that earlier estimates of radiation exposure assumed the breast and entire chest would be subjected to X rays from standard CT machines. When Boone recalculated the exposure rates based on imaging the breasts alone, the radiation dosage was no more than that of a standard mammogram.
Several research groups around the country are also working to develop breast CT scanners. But the approach is still experimental and women should continue to rely on mammograms as recommended by their physicians, Boone said.
"Even if our best hopes are realized, breast CT will not be commercially available for at least five years, and probably longer," said Karen Lindfors, a UC Davis radiologist and collaborator with Boone in developing the scanner. "Don't put off getting mammograms, because it will take some time to develop this newer technology."
Other collaborators on the project include UC Davis medical physicist Anthony Seibert and UC San Diego radiology professor Thomas Nelson. The group designed the new scanner, which sits under an examination table and rotates on a gantry parallel to the table. Boone believes it may be possible to reduce the current image acquisition time of 17 seconds per breast to as little as 8.3 seconds.
The detector was built with the goal of cancer screening, diagnosis, and image-guided therapy. A subgroup of women is of special interest: those with dense breasts, implants, and heightened risk for the disease. Early testing of the prototype showed that there is room for improvement in its contrast resolution, suggesting that future machines might be even more accurate than the original one.
The clinical trial is being conducted at the UC Davis Medical Center. Funding for the research came from the California Breast Cancer Research Program, the National Cancer Institute, and the National Institute for Biomedical Imaging and Bioengineering. Boone received a Whitaker Foundation Biomedical Engineering Research Grant in 1992 for work in CT imaging.
