COPD Detection Adds More Bang to CT Screening for Lung Cancer

Adding a short, low-dose sequence to a CT scan for lung cancer proved useful in identifying current and former heavy smokers with asymptomatic chronic obstructive pulmonary disease (COPD), a new Dutch study shows.

(Video courtesy of the Journal of the American Medical Association)

While the 2010 US National Lung Screening Trial (NLST) proved that using CT scans to diagnose lung cancer in heavy smokers reduced deaths by 20 percent compared to conventional x-rays, questions about the cost-effectiveness of doing so remain. Whether adding the ability to diagnose COPD in these patients tips the balance in favor of CT screening in this population is unclear. The study appears in the Oct. 26, 2011 Journal of the American Medical Association. (Link to published site)

Led by co-authors Dr. Onno M. Mets, and Dr. Pim Jong, of the University Medical Center, Utrecht, the Netherlands, researchers added low-dose 0.3 mSv to 0.65 mSv expiratory CT scan to the standard inspiratory CT scan used to detect cancer and emphysema.

"Lung function is the standard test (for COPD), but this may not be practical to implement in lung cancer screening," Jong told The Hub in and e-mail interview. "Therefore CT may be used to estimate the abnormal lung function."

In a video interview on the JAMA website, Jong explains that the inspiratory CT scan can show tissue destruction that indicates emphysema, while the expiratory scan shows airway diseases.

In the study, the researchers performed prebronchodilator pulmonary function testing together with the inspiratory and expiratory CT scans on the same day in 1,140 men between July 2007 and Sept. 2008 within an ongoing low-dose lung cancer screening trial.

The average age of participants was 62.5 years. Data for self-reported respiratory symptoms were available from 1,085 participants; a total of 566 participants were symptomatic, and 519 participants were asymptomatic. Forty-one participants (3.6 percent) reported physician-diagnosed emphysema and 93 (8.2 percent), bronchitis. A total of 437 men (38 percent) were diagnosed with COPD based on lung function testing.

The diagnostic model the researchers developed included five factors associated with COPD: CT emphysema, CT air trapping (an abnormal retention of air in the lungs), body mass index, pack-years (the number of packs of cigarettes smoked per day multiplied by the number of years the person has smoked), and smoking status. Using this model, the researchers correctly identified 274 patients with COPD and had 85 false-positives for a sensitivity of 63 percent and specificity of 88 percent. The positive predictive value was 76 percent, and negative predictive value was 79 percent.

These 274 participants comprised 54 percent (150 of 277) of all participants with mild obstruction, 73 percent (99 of 135) of all participants with moderate obstruction, and 100 percent (25 of 25) of all participants with severe obstruction.

"Based on the CT scan, we were reasonably accurate for the diagnosis of COPD. So we could detect almost two-thirds of the COPD patients in our population based on CT findings," Jong said in the online JAMA interview. "When you catch the disease early and give up smoking at an early stage, you will prevent the symptomatic period of the disease."

Asked about the impact of the additional scan on the cost-effectiveness debate surrounding CT scans for lung cancer screening, Jong noted that the additional information was gathered with essentially no additional cost.

"Our proposal is a fully automated analysis of the lung cancer screening CT scans, so that does not take additional costs besides the computer that is needed for the analysis," Jong said. "The CT scans are part of the lung cancer screening. Spirometry/lung function is inexpensive but impractical in a high-speed screening setting."

The authors emphasize that they are not proposing a possible strategy of using quantitative CT for detection of airflow limitation as a primary screening method for COPD noting that pulmonary function testing is the preferred method. Nevertheless, they conclude that early intervention may prevent morbidity and mortality from COPD, and because early stages of the disease are substantially under diagnosed, detection of airflow limitation may provide additional benefit to chest CT-based screening programs involving heavy smokers.

By Michael O'Leary, contributing writer, Health Imaging Hub