White highlights controversies of thoracic and cardiac screening
Dec. 3—CT scans detect cancers early, making the modality effective despite reimbursement problems and radiation risks, according to a presentation at the 93rd scientific assembly and annual meeting of the Radiological Society of North America (RSNA) in Chicago last week. Charles White, MD, director of thoracic medicine and professor of radiology and medicine at the University of Maryland Medical Center in Baltimore, also said that calcium scoring is superior to CT for detection of coronary artery disease (CAD).

CAD is the leading killer in the United States, followed by cancer, “of which lung cancer is the highest killer,” according to White,

As men and women get older, they get atherosclerosis, and their coronary arteries start to calcify, which can lead to CAD. Typically, the calcification occurs earlier than men, but “women catch up to male rates once they hit menopause.”

White compared calcium scoring, which “just looks at the calcium score,” to cardiac CT angiography (CCTA), which looks for lumen and how tight the lumen is.” White said the gating, which is the time it takes to scan a heart beat, is prospective for cardiac scoring and retrospective for CCTA. The slice thickness is 2.5 mm for calcium scoring and 0.5-0.6 mm for CCTA. The radiation dose is 2-4 mSv for calcium scoring and approximately 13 mSv for CCTA. Calcium scoring does not use contrast agents compared to CCTA. White concluded that for CAD detection, “CCTA is more invasive, and [making it] less appropriate for [CAD] screening.”

He also said that in calcium scoring, the amount of calcium correlates with the histological amount of plaque. It also provides an incremental measure of risk, and “actually shows damage to arteries,” according to White. He said that physicians look for a density of 130 or greater. Overall, White said that for judging risk, “it’s a pretty good test.”

While diabetes and smoking are both risk factors for cardiac events, a “high calcium score is a much higher risk factor,” according to White. Also, with calcium scoring, he said that “you have to look in the lungs with calcium scoring because there are other health issues that can be found, even incidentally.”

The American College of Cardiology and the American Heart Association established 2007 guidelines about those for whom this test is most appropriate:
1. Asymptomatic middle-aged men or women with at least two risk factors.
2. Patients with atypical chest pain and high negative predictive value.

“Unfortunately, most health insurance companies don’t cover this screening,” despite the guidelines, said White.

White said it is necessary to screen for lung cancer because its cure rate is 14 percent, compared with colon cancer that has a cure rate of 50 percent and breast cancer’s cure rate of 75 percent.

He said that “size versus metastasis is especially important in lung cancer. If you are able to catch it earlier, you have a better cure rate. There is a correlation between size and detection and mortality.” Though, he added that the “statistics are considered controversial, which highlights what a complex topic this is.”

The Mayo Clinic hosted the Mayo lung project in the 1980s, which included 10,000 male smokers older than 45 years. In the study groups, the clinical group (half) received chest x-rays frequently, while the other half did not. The researchers examined the five-year survival rate, which found more early cancers in the clinical group, but there was no difference in late cancer detection. Both found four cancers. According to White, “unless you can show a difference in mortality, you haven’t proven the effectiveness of screening.” He also pointed to two biases, which should be considered in the trial -- lead time bias and overdiagnosis bias.

White also said that two limitations of the trial were that mortality might not be the right endpoint and some people crossed over their groups to receive chest x-rays.

He said current advances in screening have improved detection, including digital chest x-rays and spiral multidetector CT (MDCT).

White reviewed the rationale for MDCT: availability is not a problem; the speed of the exam; a lower dose of radiation; and improved detection for smaller nodules.

In examining the justification of the costs, White said that there are 55 million smokers and 55 million ex-smokers in the United States. He speculated that if everyone in that at-risk category underwent a $200 CT scan, it would cost $22 billion with additional money needed for more work-up.

Overall, White said “CT detects lung cancer better than chest x-rays, which will surprise nobody.” CT also detects most cancers that are stage 1 and adenocarcinoma.

White acknowledged potential limitations in the current clinical trial process:
  • The study design: “non-randomized trials are widely accepted by epidemiologists and more importantly, by insurance companies, but the problem is they take a long time;”
  • False positives: “maybe up to 20 percent” experience false-positives; and
  • Overdiagnoses of indolent diseases--ground glass opacity may look like other things/airway lesions, which is very difficult to detect by CT.  
White concluded that although CT is clearly more effective at detecting early stage lung cancer, “we do not currently have the data to encourage insurance companies to pay for this.”