Standard criteria for tumor response assessment have used uni-dimensional or bi-dimensional measurements as a surrogate for volume determination. Modern CT scan techniques, in combination with algorithms developed at MSKCC, allow the calculation of tumor volume. This protocol is designed to evaluate the reproducibility of the calculated volume of pulmonary masses on separate CT scans obtained on the same day in patients with non-small cell lung cancer (NSCLC). Patients with NSCLC undergoing non-contrast CT scan of the chest will have a second, non-contrast CT scan of the chest performed. Uni-dimensional, bi-dimensional, and volume measurements for the primary NSCLC lesion will be determined on both scans and the values compared.