This study investigated variability in the interpretation of nationwide lung cancer screening CT scans, focusing on the potential of computer-aided detection and volumetry in reducing interobserver variability. The analysis involved 1,647 baseline screening CT scans from a Korean nationwide lung cancer screening project (K-LUCAS). The scans were interpreted using the AVIEW Lungscreen system implemented by Coreline Soft. There was a significant difference in per-case positive rates and per-nodule positive rates between institutional readings and a central review. The central review detected more nodules per case, but these nodules were smaller. Manual modification of semi-automated segmentation was more common in institutional readings. Inter-institution variability in positive rates was lower in the central review. The study concluded that despite the use of computerized tools, significant variability exists in CT interpretations for lung cancer screening, largely due to discarding tiny nodules and modifying segmentation results. Further investigation is needed to ascertain the benefits of reducing variability by applying stricter rules.