To Improve Lung Cancer Diagnosis, Good Medicine Is a Polymer Pill

In the top image, Zachary Levine (at left) and Joe Chen prepare to load a boxful of polymer ellipsoids into a CT scanner to test its ability to measure lung tumors’ volumes. The pill-sized ellipsoids, which mimic the density of tumors, show up clearly in the scan at bottom, allowing the scientists to determine how well different measurement protocols reveal changes in tumor size. Credit: NIST View hi-resolution version of top image View hi-resolution version of bottom image

Doctors may soon
be able to diagnose lung cancer more effectively thanks to research
performed at the National Institute of Standards and Technology (NIST),
where scientists have found ways both to increase the accuracy of
computed tomography (CT) scans and to lessen the amount of time
necessary to perceive telltale changes in lung tissue.*

For years, radiologists have determined the
size of potentially cancerous lung nodules by measuring the largest
distance across them as displayed on a computer screen in two
dimensions. A method called RECIST is widely used for this purpose, but
some members of the research community have suggested that
three-dimensional analysis, or volumetrics, may provide a better way to
determine the size of the nodules. Recently, a NIST team quantified
this improvement: Volumetrics could allow physicians to notice volume
changes that are up to 10 times smaller than RECIST can, potentially
cutting diagnosis time from six months to four weeks—a critical
difference in terms of a patient’s chance of survival.

CT scans combine a series of X-ray views
taken from many different angles to produce cross-sectional images of
the body, but there are several approaches to interpreting scan data, so
NIST’s Zachary Levine set out to determine which was best by creating a
set of reference objects that could mimic potential lung tumors. His
team measured 283 polymer-silicate ellipsoids of precise volume that
resemble pills ranging from four to 11 mm in diameter.

“For diagnosis in the earliest stage of
cancer, other studies have shown this is the size of nodule you want to
be looking at,” says Levine.

The team encased the mimics in foam rubber
and put them into layered racks of a box akin to one that holds fishing
tackle. Because foam appears transparent to the CT reconstruction, in a
scan the denser mimics look very much like tumors. The team was then
able to compare their ellipsoids’ known volumes with what the
volumetrics and RECIST methods indicated from the scan data.

“We found that volumetrics allows you to
notice volume changes that are a factor of 10 smaller than RECIST can
with a similar level of confidence,” Levine says. “This implies that you
could notice life-threatening changes from a follow-up scan performed
only weeks after the first, instead of months.”

Levine cautions that cancers often grow in
strange shapes not resembling elliptical pills which can make a
diagnosis more difficult, but that the study was a good start toward
improving data interpretation.

“Our work only applies to the simplest of
cases, but it’s still a large class of lung cancers,” he says.

* Z.H. Levine, B.R. Borchardt, N.J.
Brandenburg, C.W. Clark, B. Muralikrishnan, C.M. Shakarji, J.J. Chen,
and E.L. Siegel. RECIST vs. Volume Measurement in Medical CT Using
Ellipsoids of Known Size. Optics Express, Vol. 18, Issue 8, pp.
8151–8159, 2010.

Media Contact: Chad Boutin, boutin@nist.gov, (301) 975-4261