After performing sequential CT scans within 15 minutes, interpretations by three radiologists revealed that one-third of lung tumor measurements varied by more than 2 mm, while 3 percent of tumors qualified as having progressed within the 15-minute interval, illuminating clinically important inaccuracies in measuring tumor size and progression on CT, opined the authors of a study published online July 5 in the Journal of Clinical Oncology.

Quantitative imaging applications are increasing, portending significant benefits for oncologists and other members of patients’ cancer teams. However, several studies have identified inaccuracies enmeshed in various processes of radiologists’ review of tumors, including operator variability, CT exam performance and post-image processing.

The clinical significance of these variations has not been adequately addressed, though, because researchers have only assessed each variable independently, rather than evaluating the combined effect of these disparities, offered Geoffrey R. Oxnard, MD, and colleagues from Memorial Sloan-Kettering Cancer Center at Weill Cornell Medical College in New York City.

Thirty patients with non-small cell lung cancer (NSCLC) lesions of at least 1 cm in diameter underwent two separate CT scans within 15 minutes. Three radiologists then measured the 30 tumors without knowledge of the dates of the scans.

The 90 measurements were compared in an attempt to provide clinical information for two sets of scenarios: the degree of certainty of disease progression/patient response attainable for treating clinicians; and to help researchers adjudicate the conclusiveness of responses to novel treatments.

With a mean lesion size of 3.7 cm, a majority of measurements between CT scans varied by 1 mm or greater, while one-third varied by 2 mm or more. Half of these changes appeared as decreases and half as increases in tumor size.

The median change in tumor size between scans was approximately 4.2 percent. Meanwhile, 3 percent of measurements qualified as having progressed within the 15-minute interval, according to Response Evaluation Criteria in Solid Tumors (RECIST).

“Our data demonstrate that CT measurement of lung lesions has variability of a clinically meaningful magnitude…[T]he inherent variability of conventional unidimensional CT measurement can at times lead to the appearance of RECIST progression (20 percent diameter increase)…” Oxnard and colleagues wrote.

Eighty-four percent of the tumor measurement changes were between 10 percent increases and 10 percent decreases in size. The authors found that larger tumors tended to show wider absolute variations in measurement, while smaller tumors had greater variability relative to their size.

“We believe the variability inherent in CT imaging requires that clinicians consider other factors, such as changes in size of other lesions or patient toxicity, when using CT measurements to identify tumor progression,” the authors continued.

In view of the apparent variability of CT independent of actual changes in tumor size, Oxnard and colleagues recommended that clinicians pay close attention to other factors and to consider changes of tumor diameter of less than 10 percent to be “relatively unchanged.”