[Flat-panel detector-based computed tomography: accuracy of experimental growth rate assessment in pulmonary nodules]

To determine the performance of an a-Si/CsJ flat-panel detector-based volumetric computed tomography (VCT) prototype in volumetry of synthetic nodules in a pulmonary phantom, and to assess VCT accuracy in the assessment of hypothetic tumor growth rates based on predefined tumor doubling times.

The true volumes of 50 synthetic nodules (diameter range = 1.36 - 5.34 mm) were determined and VCT volumetry was performed before and after isovolumetric deformation of the nodules. The percent measurement error (PMF) was calculated as the percent difference of the measured from the true volume. Based on the PMF, the minimum interval between two scans was determined that would be needed to depict tumor growth corresponding to the minimum number of required follow-up days (FUDs). Based on predefined tumor doubling times (VDT) FUDs were determined before and after nodule deformation.

Measured volumes of undeformed and deformed nodules of 0.99 - 20.05 mm (3) differed significantly from corresponding true volumes (p = 0.002 - 0.004). The PMFs of these nodules significantly exceeded the values measured in larger nodules (p = 0.0001 - 0.0029). In addition, PMFs were significantly lower before than after deformation (1.33 - 7.14 % and 0.61 - 11.09 %, respectively; p = 0.002). For theoretical VDTs of 177 and 396 days, the calculated FUDs for detection of tumor growth were 19.1 and 42.7 days before deformation, and 30.2 and 67.6 days after deformation for nodules < 2 mm, respectively.

VCT allows for accurate volumetry of smallest pulmonary nodules and may become a valuable clinical tool for depiction of tumor growth of even small lesions within very short scan intervals.