Suitability of Semi-Automated Tumor Response Assessment of Liver Metastases using a Dedicated Software Package

Purpose: To evaluate the suitability of semi-automated compared to manual tumor response assessment (TRA) of liver metastases. Materials and Methods: In total, 32 patients with colorectal cancer and liver metastases were followed by an average of 2.8 contrast-enhanced CT scans. Two observers (O1, O2) measured the longest diameter (LD) of 269 liver metastases manually and semi-automatically using software installed as thin-client on a PACS workstation (LMS-Liver, MEDIAN Technologies). LD and TRA ("progressive", "stable", "partial remission") were performed according to RECIST (Response Evaluation Criteria in Solid Tumors) and analyzed for between-method, interobserver and intraobserver variability. The time needed for evaluation was compared for both methods. Results: All measurements correlated excellently (r >= 0.96). Intraobserver (semi-automated), interobserver (manual) and between-method differences (by O1) in LD of 1.4 +/- 2.6 mm, 1.9 +/- 1.9 mm and 2.1 +/- 2.0 mm, respectively, were not significant. Interobserver (semi-automated) and between-method (by O2) differences in LD of 3.0 +/- 3.0 mm and 2.6 +/- 2.0 mm, respectively, reflected a significant variability (p < 0.01). The interobserver agreement in manual and semi-automated TRA was 91.4%. The intraobserver agreement in semi-automated TRA was 84.5%. Between both methods a TRA agreement of 86.2% was obtained. Semi-automated evaluation (2.7 min) took slightly more time than manual evaluation (2.3 min). Conclusion: Semi-automated and manual evaluation of liver metastases yield comparable results in response assessments and require comparable effort.