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Old 12-17-2010, 02:29 PM   #1
Hopeful
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Better Imaging Doesn't Always Mean Better Diagnosis, Expert Says

The Gray Sheet. 2010 Dec 13, M Hogan

Researchers and clinicians trying to assess the benefits of medical imaging are trapped in a cycle of increasing imaging intensity that makes it harder to know which imaging and treatment options work best in cancer, a Dartmouth radiologist says. According to William C. Black, professor of radiology at Dartmouth-Hitchcock Medical Center, the dramatic advances in diagnostic imaging over the past two decades have led physicians to overestimate the prevalence of cancer as well as the effectiveness of interventions that follow a cancer diagnosis.

"This can lead to a cycle of increasing intensity of imaging," Black said at a Dec. 3 conference on comparative effectiveness methodology sponsored by the National Institutes of Health and the Agency for Healthcare Research and Quality.

Overdiagnosis Can Lead To Overstating Treatment Benefits

Overdiagnosis – the diagnosis of a disease more often than it is actually present – is a major problem stemming from the screening of more people with more advanced tools, Black suggested.

"With the overdiagnosis problem, you falsely label someone with the disease, you treat them for something that they don't really have, and worst of all, what you've learned from your experience is that you thought you did a really good thing," Black explained.

"But not only is it the worst thing you can do to somebody, but you actually use it as justification for doing more."

Because physicians and researchers do not know which individual patients are overdiagnosed, treatments that appear to lead to positive outcomes may actually be unnecessary, at least in some cases.

Physician biases related to advances in imaging and early detection can keep the cycle of imaging intensity going, Black said.

Cancers that progress slowly are more likely to be detected by a random imaging test rather than during the diagnostic stage when symptoms are already present. The earlier-stage detection could be the result of a deliberate screening or incidental findings during an unrelated imaging test.

"As you increase the intensity of imaging by doing a test more frequently or getting thinner cuts or improving the resolution of the image, you've effectively lowered the detection threshold for the disease you're looking for," Black said. "This will immediately lead to a higher yield of the disease, which in most clinical scenarios is considered a very positive thing immediately."

Increased use of advanced imaging "will also lead to a milder spectrum of the disease than later cases," Black continued, "and again, immediate feedback tells most clinicians that this is the right thing to do."

Over time, he added, the higher detection rates will lead clinicians to observe an apparent increase in the incidence or prevalence of certain cancers, which will then raise the issue's importance.

"Both the immediate feedback and the long-term feedback of the increasing intensity of testing will tell you – falsely – that you've necessarily done a very good thing," Black stated.

He added that the feedback cycle pertains not only to imaging but to cancer treatments.

"Any treatment that is associated with a new imaging test will look promising because the outcomes related to those cases that are detected by the improved testing are almost invariably better," he noted.

Patient-Centered Questions Include Selection Criteria

Ongoing advances in imaging technology raise real-world questions about cost, overutilization and patient risk, such as radiation exposure and the potential for unnecessary medical treatment resulting from overdiagnosis and incidental findings.

Among the most basic questions comparative effectiveness research can answer is who should be eligible for a particular cancer screening test using an advanced imaging modality such as computed tomography.

Conference speakers said the issue takes on increased relevance with the recent findings that suggest certain smokers and ex-smokers would benefit from CT chest scans to screen for lung cancer.

Interim analysis of the National Lung Screening Trial released recently by the National Cancer Institute showed a significant reduction in lung cancer mortality and overall deaths following lung cancer screening.

"This will probably change major organization recommendations," said Peter Bach, M.D., director for Health Policy and Outcomes at Memorial Sloan-Kettering Cancer Center. "Currently, no organization recommends lung cancer screening."

Incidental pulmonary nodules are found in nearly half of CT chest scans on healthy adults, Black said, adding that the issue becomes more significant as the benefits of lung cancer screening are demonstrated.

"We have guidelines for managing those [incidental] nodules, but in most cases, the guidelines say to do additional imaging," Black explained. "It's not clear when the additional imaging stops."

Black said it will be important to do statistical modeling to determine which patients to screen for lung cancer and how long they should be screened.
"We have the tendency to generalize a test to the full population largely because of the fee-for-service [reimbursement] incentive," Black said. "We have to be really careful about what are the appropriate criteria for testing."

Although randomized control trials play a role in comparative effectiveness research related to imaging, there are logistical challenges, including cost, ethical concerns and the need for large patient sample sizes.

Because imaging can be used for screening, diagnosis, staging and post-treatment monitoring for so many cancers, Black said, "we cannot do randomized trials to answer the myriad questions about diagnostic imaging." Observational studies and modeling are also needed to help answer questions about which imaging test makes the most sense, when it should be performed, and how to interpret it, he added.

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