With early diagnosis the only way to beat lung cancer, lung CAD is focused on finding tumors of 2 to 8 millimeters or more imaged via chest CT or analog or digital x-ray. While it’s too early to say if lung CAD will be successful in bringing better outcomes for lung cancer patients — it is beginning to make its mark.
The challenges of detecting lung cancer at a very early stage are formidable, but the urgency propels the development of tools for early detection. The prognosis for surviving beyond five years is abysmal — 9 to 12 percent — for patients who are diagnosed with more advanced stages of this disease. The National Cancer Institute released a report in August 2005 detailing that 160,000 people in the United States die from lung cancer each year confirming it again as the No. 1 cause of cancer deaths in this country.
Lung CAD (computer assisted detection) software has been developed for electronic analysis of both analog and digital chest radiographs and to scrutinize the large (and growing!) data sets created by multidetector CT scans. This tool is employed as a secondary read where the radiologist accepts or rejects CAD’s marked areas of interest after a primary read.
Reimbursement is critical to the adoption of new imaging technology, so it bodes well that less than a year after the 2004 Radiological Society of North America (RSNA) meeting where Riverain Medical launched its Rapid-Screen chest x-ray CAD system, the American Medical Asso-ci-a-tion issued a Category III CPT code to cover chest x-ray CAD that became effective on Jan. 1, 2006. Lung CAD for CT exams is not yet reimbursed.
Heber MacMahon, MD, a pioneer and leader in the development of lung CAD, professor of radiology at the University of Chicago and consultant to Riverain Medical, explains that even the most conscientious and careful radiologist can overlook suspicious nodules. Fatigue is one factor as these clinicians are expected to read more studies in a shorter period of time and in the case of CT, the exponential increase in the quantity of images produced by the multidetector scanners.
Lung CAD and the ubiquitous chest x-ray
Chest x-rays are the most requested examination ordered in a hospital because they are required not only for symptomatic patients, such as those with suspected pneumonia or heart disease, but also those patients considered asymptomatic such as those scheduled for surgical procedures other than those involving the heart and lungs.
MacMahon notes that while chest x-rays are not currently recommended for lung cancer screening, many malignant nodules are picked up incidentally in routine chest x-rays. “In other words, the patient is completely asymptomatic from the cancer, and he or she has a chest x-ray for another reason. If we can detect a questionable lesion on x-ray, that may help.”
He explains that while CT scans are capable of detecting nodules that are 2 millimeters in size, even with CAD under ideal conditions, lung nodules of 5 millimeters push the limits of detection on a chest x-ray. On the other hand, he notes that a very high proportion of nodules that are less than 5 mm are benign, and the more important nodules are 8 mm and larger. Additionally, he anticipates that the accuracy of lung CAD will improve in sensitivity while decreasing the number of false positives that are presented. A false positive might include marking normal anatomy, focal scars or other abnormalities, and they prove to be a distraction for the radiologist and may slow reading times.
Greig Huggins, vice president of business development for the Utah Imaging Associates in Salt Lake City, says their 33 radiologists who cover six hospitals plus, selected the Riverain RapidScreen chest x-ray CAD system to use in analyzing virtually every chest x-ray they review. The system identifies areas of interest that are suspected nodule sites for both analog and digital chest images. In their clinical trials for pre market approval, Riverain demonstrated a 23 percent increase in radiologists’ detection of solitary pulmonary nodules for early stage lung cancer (9-14 mm) when RapidScreen was used. The installed base now numbers about 200.
The RapidScreen system resides on a central server connected to PACS in their basic six hospital network, but is waiting for the hospital protocols to be completed before full deployment of the automated processes. Workflow includes routing DICOM chest x-ray images into the system, and following processing activities,