Lung CAD: A Closer Look

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Lung CAD: A Closer LookCan software boost early detection for lung cancer enough to reduce the death rate?  Probably, eventually, but the studies haven’t shown it just yet. And few want to pay extra for it — not hospitals or radiologists or insurers — until solid proof is in hand. But in its clinical capabilities, there are for sure believers.

Lung cancer is the No. 1 cancer killer in the U.S. — mainly because it’s usually diagnosed too late to offer effective treatment. The trick is to detect small lung nodules — 30 millimeters or smaller — and distinguish the benign ones from those that could be malignant. Then the suspicious ones have to be tracked to see whether they are growing, and how fast. All of these things are hard to do.
Only 16 percent of lung cancers are diagnosed at an early enough stage that the available therapies can give the patient a 50-percent shot at surviving for five years or more, according to the American Cancer Society.  

With those odds, a tool to increase the frequency of early diagnosis ought to be welcomed. Computer-aided detection for lung applications — lung CAD — has been approved by the FDA since 2001 for chest radiography, and since 2004 for computed tomography lung scans. Vendors large and small offer products either as stand-alone workstations or integrated into CT scanners or radiography systems (see sidebar on page 44). The applications flag suspicious areas on a scan for the radiologist to take a closer look. They can act as a check, or second read, on the radiologist’s initial evaluation. On follow-up scans, CAD can be used to track whether lung nodules have changed in size or shape.
Though both radiologists and market observers expect lung CAD to be part of the standard of treatment someday, it hasn’t generated a groundswell of enthusiasm so far, for a variety of reasons.

Solid potential

Melissa Ginsburg, MD, director of general radiology at Memorial Sloan Kettering Cancer Center, in New York, has looked at CAD for lung CT, and thinks it has the potential to be helpful, but solid research is lacking. “A couple of studies have come out, but we’d like to see a few more that prove accuracy,” she says.

Existing studies on CAD for lung CT aren’t adequate to draw any conclusions, says a recent study by ECRI of Plymouth Meeting, Pa. Most of the studies were too small, the authors said, and many used retrospective techniques, like having the CAD software analyze existing images where the correct interpretation was already known. A “gold standard” study — prospective, with large numbers of subjects and a control group — hasn’t been published yet. The ECRI report didn’t address the use of CAD with radiography images.     

There are fewer than 200 lung CAD units in use in the U.S., including both radiography and CT applications, according to Frost and Sullivan. About 40 percent of the units are used with CT, and the balance with radiography.  In contrast, the firm says that CAD for mammography — the earliest application of CAD, approved in 1998 — boasts almost 3,500 units. 

Eyeing growth

“More studies need to be done on lung CAD,” says Subha Basu, a Frost and Sullivan industry analyst for healthcare and medical imaging. “Mammography CAD has proved itself. We have quite a bit of data on picking up breast malignancies. With lung CAD, those studies are just being initiated. In the next three to four years, we’ll see how good the products are.” He predicts 20 to 30 percent growth per year for lung CAD until 2012, as studies are released and use becomes more widespread. 

Another reason for the large discrepancy in market penetration between mammography and lung CAD applications is that, unlike chest x-rays or lung CT, mammography is used for routine screening, so the procedure volumes are much larger. There’s considerable scientific debate as to whether lung screening would accomplish the desired goal — catching cancers while they’re still curable — in enough cases to make the enormous cost worthwhile.
A study of 31,000 current and former smokers published in the October New England Journal of Medicine suggested that lung CT indeed can help identify early-stage cancers, but the study lacked a control group and won’t settle the issue on its own. The National Cancer Institute’s National Lung Screening Trial, a prospective, randomized and controlled study of 50,000 current and former smokers, is intended to measure the value of lung screening, for both radiography and spiral computed tomography. But results aren’t