Fig. 1

a Scatter plot of the bivariate survival copulas (PFS by RECIST vs OS); b scatter plot of the bivariate survival copulas (PFS by Choi vs OS). Interpretation of axes (a, b): progression-free survival (vertical) and overall survival (horizontal). c Δ Sum of diameters (%) and average Δ of tumour density (%) at 6 months; d Δ sum of diameters (%) and average Δ of tumour density (%) at 3 months. HU Hounsfield units, PFS progression-free survival, OS overall survival, SE standard error