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Medical Community Divided on Scans

How much scientific evidence is required to put new technology into general use?

Part two of a two part series. Both are part of an occasional series on new health information.

The advisability of CT screening is quite a controversial issue in the medical community, and even within the radiology community itself. Medical journals have published numerous articles arguing both sides of this issue.

“Mainstream radiology is very skeptical about it,” says Dr. William Casarella, Professor and Chairman of the Department of Radiology at Emory University School of Medicine. Involved is a fundamental question about how much scientific evidence is required to put new technology into general use.

One view, held by various medical organizations, is that a screening tool should only be used when certain types of evidence have been gathered about the disease of interest, the benefits, harms and costs of the tool, and about the effectiveness of available treatments. This conservative view is reflected in statements such this one in a letter to a radiology journal, “It is essential that large, well-designed studies support the belief that the benefit of CT screening outweighs the risk before we recommend this procedure.” There is wide agreement that this evidence does not exist for CT screening, whether it is whole body or individual scans.

Screening appeals to our strongly held belief that early detection allows more effective treatment and leads to better health outcomes. While this seems to make sense intuitively, so far it has only been proven for a few conditions. It may surprise you, for example, that there is no proof that screening for lung or prostate cancer reduces death or prolongs life. Because of these uncertainties, the National Cancer Institute launched a major trial of screening for prostate, lung, colon and ovarian cancer about 10 years ago (still ongoing). Recently, a new trial of screening for lung cancer by CT scan was just added.

A number of organizations, taking note of the trend toward consumer-driven CT screening, have adopted conservative positions and issued cautionary statements. The American College of Radiology has said that there is no evidence that total body CT screening is effective in prolonging life. It is “concerned that this procedure will lead to the discovery of numerous findings that will not ultimately affect patients’ health but will result in unnecessary follow-up examinations and treatments and significant wasted expense.” On its website (www.fda.gov/cdrh/ct/), the FDA states, “ ...the potential harm to the individual may be greater than the presumed benefit.”

The AMA issued a report earlier this year, stating, “…None of these [CT] screening tests have been shown to reduce disease-specific mortality…” and “There is no evidence to date to support the use of a “total body scan” as an appropriate or effective tool in the early detection or prevention of disease. Such services are not evidence-based and are not consistent with accepted guidelines for screening.”

The American College of Chest Physicians, the Food and Drug Administration, the Environmental Protection Authority, the American Association of Physicists in Medicine and the American Cancer Society have taken similar positions. Both Texas and Pennsylvania have issued statements against self-referred CT screening. As for the heart scan, in their report from a recent conference, the American College of Cardiology/American Heart Association state, “A policy of self referral to atherosclerosis imaging tests remains premature and should be the subject of formal effectiveness study prior to widespread adoption of this practice.”

The other view is that when we have technology that seems to have “low risk and high value,” we should use it “until its value is disproven.” “If we wait for evidence there is the risk of losing years of a good tool waiting for results which may be wrong or unclear.” Some in this camp argue, “That we may be doing more harm than good is speculation; the reality is that most medical practice lacks rigorous scientific proof of value.” They seem to be saying that we have practiced medicine without a firm scientific basis in the past and still do, in large part, so why hold up promising new practices to wait for evidence of a net benefit. This is contrary to the widespread trend of recent decades toward evidence-based clinical practice.

In today’s world, technology seems to advance faster than it can be evaluated clinically. When definitive evidence is lacking, agreement among experts may be difficult to obtain. Rational physicians and scientists who are aware of the evidence and the uncertainties, may end up taking quite different positions. For some, it is enough, for example, to demonstrate that a screening tool detects more disease. For others, the standard is that it must prolong life. Still others require evidence that, overall, it does more good than harm.

Should you accept the invitation to get a CT screen? It seems to depend on your comfort with the risk of missing something versus the risk of unnecessary procedures or treatments, and how firmly based in evidence you want interventions to be before you will accept them. A number of bodies of the medical establishment, including the American College of Radiology, have taken the view that CT screening, especially self-referred, should not be undertaken before the evidence for benefit is in hand.

Last year, the Women’s Health Initiative trial of a widely used combined hormone therapy concluded “Overall health risks exceeded benefits…” The risks of medical interventions are not trivial. Harm outweighing benefit really does seem to occur. Caution seems advisable.

Mark H. Zweig, M.D., previously a staff physician at NIH, has more than 35 years of experience in medical research and 25 years in patient care.