CT Scans for Lung Nodules OK at Just 3% of Typical Dose

Radiation doses as low as one-thirtieth of the typical exposure are enough for follow-up screening of lung modules, according to a new study in the September edition of the American Journal of Roentgenology.

The study, conducted at the Stanford University and the University of Bern in Switzerland, found that tube current-time settings could be as low as 10mAs - well below the standard 100 to 300 mAs - without compromising diagnostic image quality. Lower tube current-time settings mean a sharp drop in radiation dose. That’s particularly important for patients with lung nodules, who often undergo repeated CT scans to monitor for lung cancer, the researchers said.

“The risk of radiation induced cancer death for one standard chest CT is estimated at roughly one in 4,000 and could be reduced hypothetically to one in 120,000 with this low dose protocol,” said radiologist Andreas Christe, MD, of the University of Bern, a lead author of the study.

Three radiologists reviewed chest CT images of 50 patients. The images had been reconstructed at different dose levels. The radiologists were able to identify an average 88 percent of the lung nodules at 10 mAs compared to an average 91 percent at 300 mAs.

In his clinical practice, Christe monitors lung modules at 40 mAs because the study used dose simulations and smaller fields of view than is routine in clinical practice. But pending the results of a follow-up clinical study, he may reduce dose further, he said.

The study also found that computer-aided volume measurement in the follow-up of lung nodules decreased the variability found when radiologists did the measurements manually.