Variable Importance Relative Importance GEO_volume             0.0139 1.000 GEO_fx_pruned         0.0073 0.521 IHIST_entropy          0.0042 0.305 GEO_ROI_VA_ratio      0.0037 0.268 IHIST_p10tile          0.0025 0.182

Table 2: Five image variables used for CT textural analysis. Abbreviations: IHST_entrop = entropy, IHIST_p10tile = histogram 10 percentile, GEO_volume=tumor volume, GEO_ROI_VA_Ratio = volume-to-area ratio, and GEO_fx_pruned=fraction GTV pruned after thresholding. The importance measure of a variable is the value of prediction error of the entire model (i.e. all the variables) subtracted from the error of a model containing randomized values for that variable. The relative importance value is simply the value of importance measure divided the maximum possible importance value across all the variables.