Table 2. Quantitative metrics extracted from lesion ROIs on PET images. Radiomics-based metrics described are second-order metrics from gray-level co-occurrence matrix (GLCM) (13).

Metric	Description
MTV	Volume of ROI
SUVmax	Maximum uptake within tumor ROI
SUVpeak	1 cm sphere surrounding SUVmax
SUVmean	Mean of all uptake values within tumor ROI
TLG	Product of SUVmean and ROI volume
SUVstdev	Standard deviation of uptake values within tumor ROI
Homogeneity	Measure of closeness of elements along the diagonal of GLCM, inversely correlated with Entropy-GLCM
Entropy-GLCM	Measure of randomness in GLCM, thought to provide measure of heterogeneity
Dissimilarity	Measure of variation in pairs of GLCM

ROI, region of interest; PET, positron emission tomography; MTV, metabolic tumor volume; SUV, standardized uptake value; TLG, total lesion glycolysis.