Cancer imaging innovations at UC Davis enhance tumor detection
UC Davis is home to a breast cancer innovation: a dedicated CT scanner that may be better than mammography at screening for breast cancer and could spare some women biopsies.
The breast CT is much more comfortable than a mammogram, as well.
The device, developed by vice chair and professor of radiology John M. Boone, is perhaps the centerpiece of UC Davis’ cancer imaging projects with translational impact, which encompass 18 researchers working to improve the x-rays, CT scans, MRIs and other techniques now used for patients with cancer.
The imaging projects aim to bring technologies that begin as ideas at the basic science level into clinical trials and eventually into routine medical practice.
Other projects include Simon Cherry’s positron-emission tomography (PET) imager, which should allow researchers to watch how a potential drug works in mice before it is used in humans. Though sized for mice, the PET imager is not a small contribution, and already has helped in the creation of a combination breast imaging machine combining PET with CT (computed tomography).
Boone decided several years ago that traditional mammograms had significant limitations and that the possibility of revisiting the potential of CT was warranted. Mammography often misses small growths or breast lumps.
“Especially in women with dense breasts,” Boone wrote in an article, “the shadow of a breast tumor can easily be hidden within the complicated background structure of the glandular tissue.”
To get better images, investigators had explored the use of CT back in the 1970s. But the technology was abandoned because the detectors that picked up the CT radiation shown through the breast were not good enough, and so too much radiation had to be used.
Traditional mammography shines x-rays through the breast a single time and in one direction, producing images like a shadow that outlines structures. A CT scanner shines x-rays through the breast as well, but the source that emits the x-rays and the detectors that pick them up on the other side of the breast are mounted on a rotating platform, which spins while taking multiple images. A computer combines the many individual x-ray images into a stack of CT images, almost as if you were viewing the slices of a loaf of bread, and photographed what was inside – although with black and white film.
Boone built the first dedicated breast CT scanner using off-the-shelf parts and custom-designed parts fabricated at a local machine shop. That machine has now been sent to the University of Pittsburgh, which is taking part in a trial with Boone and his group, and Boone has built a second machine now in use at the hospital.
Breast cancer screening is typically an annual procedure, so radiation dose is an important concern. Because the geometry of radiation exposure with breast CT was unique, Boone had to develop the dosimetry tools necessary to accurately compute radiation dose to the breast. These techniques became the basis of the dose selection in breast CT. The scanner settings are adjusted so that the dose of the breast CT examination is the same as for traditional mammography screening. There is also reason to believe that radiation exposure from breast CT as currently performed is even lower than mammography for most women.
In a report on the first 79 women scanned, Boone and radiologist Karen Lindfors, chief of breast imaging at the UC Davis department of radiology, found that breast CT was significantly better than mammography for seeing and picking up masses, which may or may not be cancer. Boone, Lindfors and the other authors said breast density made no difference to the CT scanner. And, perhaps as importantly, the subjects found the scanner much more comfortable than having their breasts compressed in the mammography machine.
Breast CT presently is limited in its ability to reveal the tiny calcium deposits known as microcalcifications that sometimes signal cancer and sometimes are benign. Much has been made of that shortcoming. Boone, however, says this is not a problem. Because mammography is good at picking up microcalcifications, the technologies complement each other. His group also is building a scanner that will detect microcalcifications better, he says.
In addition, physicist Ramsey Badawi is working with Boone to wed the breast CT scanner with PET. The enhanced images may be useful for women who have had lumpectomies and whose scar tissue makes it difficult to look for recurrence using x-ray alone.
Boone is reluctant to predict exactly what role breast CT might have eventually, whether it could replace mammography, or whether it would be used after a woman had a suspicious mammogram to better examine the area before subjecting her to a biopsy.
But it will have a role, he says. A breast CT scanner will cost more than a mammography machine, about twice as much, but it should cost less and be more convenient than some other technologies being explored for breast cancer detection, such as MRI.
Martin Yaffe, an imaging expert at the Sunnybrook Health Sciences Centre in Toronto, says he is fairly confident there will be a role for breast CT in clinics. He calls the results to date “extremely impressive.”
“Dr. Boone really is the pioneer of CT mammography,” he says. “He seized the opportunity to have a fresh look at the potential of that technology.”