"We think this technology may allow radiologists to routinely detect breast tumours at about the size of a small pea", stated John M. Boone, professor of radiology and biomedical engineering at UC Davis and the machine's developer. "In contrast, mammography detects tumours that are about the size of a garbanzo bean. Tumour size at detection is one of the most important factors in determining breast cancer prognosis, so if we can detect smaller cancers and do so routinely, survival from this disease will improve."
Unlike mammography, in which the breast is squeezed between two plates, the breast CT machine requires no breast compression.The patient lies face down on a padded table. The table has a circular opening in it, through which the patient places one breast at a time. A CT machine under the table scans each breast. The screening takes about 17 seconds per breast.
"There was no discomfort", stated Lydia Howell, a professor of pathology at UC Davis and a volunteer in preliminary clinical testing of the breast scanner. "But the more important advance will be if breast CT does detect tumours earlier than mammography. 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."
A mammogram is an X-ray taken through all the layers of the breast at once. The resulting image may not detect a tumour hidden by other structures within the breast. This is more likely to happen in the case of young women with dense breasts or in women with breast implants. The breast CT scanner takes images of virtual "slices" of the breast - about 300 images per breast. Computers then assemble these images into highly detailed, three-dimensional pictures that provide a more unobstructed view of breast tissues than can be seen on mammography.
"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. Your chances of finding a particular person in the crowd are going to be a lot better with more photos", John Boone stated.
Professor Boone and his colleagues are testing the new technology in a clinical trial that will enroll about 190 patients. The trial is open only to UC Davis patients with recent mammograms that are suspicious for breast cancer. Women who agree to participate in this trial have the breast CT examination followed by a needle biopsy of the suspicious tissue. If the trial confirms that breast CT detects tumours as well as mammography, as investigators expect, the next step will be a larger trial to determine whether the new technology can indeed detect tumours earlier than mammography. Professor Boone believes that a more extensive trial could be under way within two to three years.
John Boone developed the machine in collaboration with UC Davis radiology professors Karen K. Lindfors and J. Anthony Seibert, and UC San Diego radiology professor Thomas R. Nelson. The breast CT project was funded by $6 million in grants from the California Breast Cancer Research Programme, the National Cancer Institute and the National Institute for Biomedical Imaging and Bioengineering. "Of course, we are going to let the science dictate where we go with this", Professor Boone stated, "but if all goes well, breast CT may be the breast cancer screening technology of the future."
John Boone, a medical physicist who holds six scientific patents, has served as a consultant to the National Institutes of Health, the U.S. Food and Drug Administration and the U.S. Army Breast Cancer Research Programme. He is vice chair for research in the UC Davis Department of Radiology and co-leader of the UC Davis Cancer Center Biomedical Technology Programme.
Computed tomography, sometimes called "CAT scanning", is used every day to scan brains, lungs, abdomens and pelvises. But imaging experts long ago dismissed CT as impractical for breast cancer screening, assuming it would require too much radiation. Professor Boone and his colleagues decided to revisit the issue, recognizing that radiation-dose estimates for breast CT were based on use of standard CT machines, which would require the breast and entire chest to be scanned together. When John Boone recalculated radiation doses based on scanning the breast alone, he found that CT imaging would use no more radiation than mammography.
Scientists at the University of Rochester, the University of Massachusetts, and Duke University are also developing breast CT scanners, but Professor Boone's is the first to have reached clinical testing. "A number of talented scientists around the country are working on the development of this new tool, and this friendly competition keeps us all working that much harder to produce results", John Boone stated.
For now, women should continue to get mammograms as recommended by their physicians. "Although the breast CT images are interesting, mammography is the currently accepted gold standard for breast cancer screening, and women should continue to get their annual mammograms", radiologist Lindfors emphasized. "Even if our best hopes are realized, breast CT will not be commercially available for at least five years, and probably longer. Don't put off getting mammograms, because it will take some time to develop this newer technology", she stated.