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‘Changes’ In Lung CT Scans Fool Radiologists

July 20, 2011
Written by: , Filed in: Chest Radiology
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Researchers asked three experienced radiologists to read 30 pairs of chest CT scans, each set from a patient with late-stage lung cancer. On a few of the scans, the radiologists found changes in tumor size—ranging from shrinkage of 23 percent to growth of 31 percent.

Except that the tumors hadn’t changed in size at all. For each patient, the pair of CT scans had been taken no more than 15 minutes apart. Any perceived change in size derived simply from the unavoidable lack of precision in CT scans. The smaller the tumor, the larger the perceived variation between the two scans.

Gregory Riely, MD, PhD, a lung cancer specialist at Memorial Sloan-Kettering Cancer Center in New York, is corresponding author for the study, which was published online earlier this month in the Journal of Clinical Oncology. In an interview, he told Reuters Health:

The patient and the doctor both need to understand that small changes don’t necessarily mean much. Changes of up to 10 percent can happen simply as a result of the inherent variability of CT imaging.

This is not just an academic exercise. Three percent of the tumors appeared to have grown so much that doctors would normally diagnose progression of the disease. That might mean that a treatment that actually was working might be discontinued in the belief that it had been ineffective.

The study’s results also have major implications for clinical trials of anticancer drugs, the effectiveness of which is measured by whether and how much they cause tumors to shrink—as shown on CT scans. In fact, three authors, in an accompanying editorial, concluded that when it comes to evaluating anticancer drugs, “It is time to cast away familiar conventions and turn to better methods.”

Michael Maitland, MD, PhD, a medical oncologist at the University of Chicago Medical Center, is one of the authors of that editorial. He told Reuters Health:

This is telling us scientifically how much noise is naturally there without any treatment or the cancer getting worse.

Related seminar: Cardiovascular & Pulmonary Imaging (all-new release)

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