Lung CAD tracks growth of suspected tumors

April 1, 2007

The specter of lung cancer hangs over a generation who grew up in homes where ashtrays were as common as shag carpeting. Those youngsters, now entering their 50s and 60s, may have smoked and may have quit, but the risk of cancer remains.

The specter of lung cancer hangs over a generation who grew up in homes where ashtrays were as common as shag carpeting. Those youngsters, now entering their 50s and 60s, may have smoked and may have quit, but the risk of cancer remains.

The prospect that CT might find the earliest signs of cancer, or provide peace of mind in its absence, has led some in this generation to seek out the modality. Others struggling with respiratory problems have sought answers through the far more common chest x-ray. For both, lung computer-aided detection offers the potential to find lesions that might otherwise elude human eyes.

When applied to CT data sets, it can help spot lesions as small as 3 mm. Alternatively, CAD software applied in chest radiography can help identify lesions as small as 9 mm.

Dr. Heidi Roberts, an associate professor of radiology in the department of medical imaging for Princess Margaret Hospital in Toronto, describes ImageChecker CT Lung, a software program developed by Hologic/R2, as very useful. False positives have gotten down to a "very bearable minimum," she said. It's so useful, in fact, that she wishes it were on the hospital's PACS rather than a dedicated workstation.

"The only reason we don't use it more often is that we have to get up, go to the workstation, and open the case again," she said. "With the workload we have, that is not always possible."

R2's CAD algorithms examine the CT data in 3D, automatically detecting potential areas of interest, assisting in the detection of solid lung nodules, then measuring them. An algorithm even calculates the percentage of calcification in lesions, a key parameter in determining whether they are cancerous.

But ImageChecker CT, which is in use at Princess Margaret Hospital as part of a lung cancer screening study, cannot provide a definitive diagnosis of cancer. Nor can any other lung CAD for CT.

"It is not a problem with the software. It is a problem of the disease," Roberts said. "Whether the radiologist finds the nodule or the software finds it doesn't matter. It is still difficult to figure out."

Half the population has some nodules, and more than 90% of these are benign, she said. Once small lesions are detected, lung CAD might be used to track the growth of nodules so as to gauge the character of the lesion based on its aggressiveness. Other modalities, such as PET, might be used to gain more information or a CT-guided biopsy might be employed, if the nodule is large enough. When treatment is ordered, CAD can track the size of the nodule to assess its effect.

These detection and measurement capabilities are staples found in lung CAD programs. GE Healthcare's Lung VCAR (volume computer-assisted reading) finds, isolates, and measures lung nodules found in CT data, tracking nodule growth over time. Ditto for Siemens Medical Solutions' syngo Lung CAD, part of the company's LungCARE CT product.

And lung CAD is not constrained to just CT. At the Ogden Clinic in Utah, Dr. Mark Alder uses a CAD program called RapidScreen to check chest x-rays. This software, developed by Deus Technologies, now called RiverRain Medical, came on the U.S. market some five years ago. It has been groomed to detect early-stage lung cancer, identifying solitary pulmonary nodules between 9 mm and 30 mm, as well as other suspicious nodules, on chest x-ray. Alder, the only radiologist on staff at the 50-physician clinic, looks at RapidScreen as a safety net.

"Having this second reader is one way a solo guy like me can always be at his best," he said.

Since RapidScreen was installed at the clinic two years ago, the computerized assistant has confirmed several cases of lung cancer that Alder found on his own. It also spotted one he missed. Everyone getting a chest radiograph, regardless of the reason, goes through a lung CAD screen.

"You want to be sure that in your search for pneumonia or bronchitis, you don't forget to look for lung cancer," he said.

A CPT code in place since 2005 has paved the way for payers to cover lung CAD. Many have responded with reimbursement, albeit typically less than $30 per case. But reimbursement is not an issue at Ogden Clinic, which has a sweetheart deal with the maker of RapidScreen. The clinic pays RiverRain on a per-click basis-and only if it receives reimbursement for the use of the lung CAD. At the same time, having RapidScreen onboard differentiates the clinic from competitors.

"It sets us apart from other radiology groups in the community," Alder said. "With these advantages and the fact that it's impossible for us to lose money on it, lung CAD is really a no-brainer."