Towards volumetric thresholds in RECIST 1.1: Therapeutic response assessment in hepatic metastases

Objectives To empirically determine thresholds for volumetric assessment of response and progress of liver metastases in line with the unidimensional RECIST thresholds. Methods Patients with metastatic colorectal cancer initially enrolled in a multicentre clinical phase-III trial were included. In all CT scans, the longest axial diameters and volumes of hepatic lesions were determined semi-automatically. The sum of diameters and volumes of 1, ≤2 and ≤5 metastases were compared to all previous examinations. Volumetric thresholds corresponding to RECIST 1.1 thresholds were predicted with loess-regression. In sensitivity analysis, the concordances of proposed thresholds, weight-maximizing thresholds and thresholds from loess-regression were compared. Classification concordance for measurements of ≤2 metastases was further analyzed. Results For measurements of ≤2 metastases, 348 patients with 629 metastases were included, resulting in 4,773 value pairs. Regression analysis yielded volumetric thresholds of -65.3% for a diameter change of -30%, and +64.6% for a diameter change of +20%. When comparing measurements of unidimensional RECIST assessment with volumetric measurements, there was a concordance of significant progress (≥+20% and ≥+65%) in 88.3% and of significant response (≤-30% and ≤-65%) in 85.0%. Conclusions In patients with hepatic metastases, volumetric thresholds of +65% and -65% were yielded corresponding to RECIST thresholds of +20% and -30%. Key Points • Volumes and diameters of liver metastases from colorectal cancer were determined. • Volumetric thresholds of +65%/-65% corresponding to RECIST 1.1 are proposed. • Comparing both measurements, concordance was 88.3% (significant progress) and 85.0% (significant response).