Digital Breast Tomosynthesis: The Past and The Future

SenoClaire, a new breast tomosynthesis system developed by General Electric in collaboration with Massachusetts General Hospital, received FDA approval in September. Using digital breast tomosynthesis (DBT) for breast cancer screening allows radiologists to detect smaller cancers earlier than with standard two-dimensional mammography, and reduces recall rates, according to recent studies. According to Daniel Kopans, MD, senior radiologist in the breast imaging division, department of radiology at the hospital, DBT will replace mammography in the next two years as the standard of care. Diagnostic Imaging spoke with Dr. Kopans about his role in the development of DBT, breast cancer screening, and the technology’s future.

Can you give a brief timeline of when tomosynthesis began to be used for breast cancer screening?
Well, it's actually a very long story. It goes back to 1978 when I became head of what would develop into the breast imaging division at Massachusetts General Hospital. I was frustrated by the fact that we could see something on a mammogram, but the surgeons couldn't feel it. I had developed a “localization wire,” which could be placed in a lesion that we found at screening to direct the surgeons to the lesions in the operating room.[[{"type":"media","view_mode":"media_crop","fid":"28144","attributes":{"alt":"","class":"media-image media-image-right","id":"media_crop_8529790283138","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"2820","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"float: right; height: 220px; width: 200px; border-width: 0px; border-style: solid; margin: 1px;","title":"Daniel Kopans, MD, senior radiologist, breast imaging division, department of radiology, Massachusetts General Hospital","typeof":"foaf:Image"}}]]

They would then send us the excised tissue for confirmation. The X-ray of the tissue showed the cancers with much greater clarity than we could see when they were still inside the breast. This was, in large part, because the normal breast tissue in front and behind the lesion was hiding the cancer. I wanted to find a way to see the cancers more clearly. The so-called polytomography required too much X-ray dose and computed tomography was in its infancy.

Were there any other options at the time?
One of the technologies in use was the polycycloidal tomography, where you could blur out everything in front and in back of a plane of interest and see that plane with greater clarity. For every plane that you wanted to see, you would have to do a full X-ray exposure and so to go through the entire breast would be prohibitively dose-intensive.

So what was your plan?
I had read about this idea of tomosynthesis, where you could take a few images from different angles and then use a computer to synthesize every plane through the breast from a few low-dose images. I realized that this would really solve one of the major problems that we as radiologists had. The problem was that this was 1978 and there were no digital detectors, so we couldn't get the information into a computer and the computers were pretty rudimentary at that point.

I had to wait until the 1990s, early 1992, when my research director, Richard Moore, and I were joined by physicist, Lauren Nicolson. Then, we at Mass General joined in what was called the ‘National Digital Mammography Group,’ which was formed to try and help the companies develop digital mammography. My team recognized that General Electric had the best detector for doing what we wanted to do, which was digital breast tomosynthesis. And so we partnered with General Electric and while we were helping them develop a digital technology, we started developing digital breast tomosynthesis and – to make a long story short – we proved the concept with phantom material and mastectomy samples. We got a patent, which was issued in 1999.

How did you get funding?
It’s interesting. Congress had established a program to support breast cancer research and we received a grant from the Army to develop DBT. So the Army was funding breast cancer research projects. This money allowed General Electric to build the first prototype for us. Then we started doing images of volunteers in 2000. And we were able to show almost right away that tomosynthesis could find more cancers than we were finding with two-dimensional mammography and also eliminated some of the problems that come with two-dimensional mammography.

How does tomosynthesis work?
If you can imagine a book that has clear pages, the print is on the pages but the pages themselves are clear. You can hold a book up to the light and see all the words, all the way through the book, but they superimpose one on top of the other. It makes it very difficult to read the words. A conventional 2D mammogram is the whole book. You're seeing from one side of the breast to the other, and tissue structures on one side superimpose on tissue structures all the way through – and they can hide cancers. In addition, they can superimpose and look like there's a cancer when in fact it's just normal tissue adding up.

With DBT, we're able to create the pages of the book so that you can look through the breast, essentially one page or one plane at a time, and see cancers with much greater clarity. We can see some cancers that were hidden by the normal tissue. A side benefit is that normal tissue that looked like it might be a cancer, because it was superimposing, disappears on tomosynthesis because you no longer have superimposing tissues.

Is this type of screening beneficial for all women or just those with dense breast tissue?
DBT makes it easier to find small cancers in women with all tissue types, including women with all fatty tissue. What can look like a vague, unimportant shadow in a fatty breast on 2D mammography becomes highly suspicious ‘spiculated’ mass on DBT. DBT will replace 2D mammography for screening all women because it is a better mammogram.

How does this affect recall rates?
We knew right off the bat was that this technology was going to be able to find more cancers and was going to decrease the so-called false-positive rate.

The recall rate is about 10% for 2D mammography which, by the way, is identical to the recall rate for having a pap smear. So it's interesting that mammography is singled out as being too high. But anyhow, tomosynthesis reduces the recall rate.

What would you like to say to radiologists about DBT?
They should be aware that this is a technology that will save more lives. The whole reason for doing any breast imaging at all, quite frankly, is to find breast cancer earlier, to save lives, and screening is the way to do that. It's been shown over and over again that the more small cancers that you find, the more lives you save. This is going to find more cancers and more lives will be saved.

One of the other concerns is DCIS. Opponents of screening say, ‘Well, mammography finds all these early cancers,’ and you and I would say, ‘Well, that's good. You find it before it's invasive and it's completely curable.’ Two-dimensional mammography is actually very good at finding DCIS. I don't think we need to actually improve on that and interestingly, tomosynthesis doesn't actually find more DCIS. It finds more small invasive cancers and it's invasive cancers that are the ones that can be lethal

The concern is, and the belief is, that by removing DCIS, you prevent someone from developing an invasive cancer. I think that's actually the truth but there's a lot of legitimate debate about that. But there's no question about invasive cancers. Invasive cancers can spread to other parts of the body and that's what kills people, metastatic disease, that are in the organs. So, finding invasive cancer before they metastasize is really the goal of efficacious screening.

I think the doctors need to know that the increases in detection of invasive cancers, the small invasive cancers when they are small, will translate into saving more lives without increasing the recall rate and without increasing the detection of DCIS.