Small pulmonary nodules: Volumetrically determined growth rates based on CT evaluation

PURPOSE: To determine the accuracy of high-resolution computed tomographic (CT) volumetric measurements of small pulmonary nodules to assess growth and malignancy status. MATERIALS AND METHODS: The accuracy of three-dimensional (3D) image extraction and isotropic resampling techniques was assessed by performing three experiments. The first experiment measured volumes in spherical synthetic nodules of two diameters (3.20 and 3.96 mm), the second measured deformable silicone synthetic nodules prior to and after their shape had been altered markedly, and the third measured nodules of various shapes and sizes. Three-dimensional techniques were used to assess growth in 13 patients for whom the final diagnosis was known and whose initial nodule diameters were less than 10 mm. By using the exponential growth model and the calculated nodule volume at two points in time, the doubling time for each subject was calculated. RESULTS: The three synthetic nodule studies revealed that the volume could be measured accurately to within +/-3%. All five malignant nodules grew, and all had doubling times less than 177 days. Some malignant nodules had asymmetric patterns of growth identified by using the 3D techniques but not the two-dimensional methods. All eight benign nodules had doubling times of 396 days or greater or showed a decrease in volume. CONCLUSION: CT volumetric measurements are highly accurate for determining volume and are useful in assessing growth of small nodules and calculating their doubling times.