Table 4.

Summary of the methods used in the reviewed studies.

Study and year	Data source	External validation	Feature type	Feature extraction	Feature selection	Segmentation
Cho et al. 2018	Public	Training + testing	First-order and second-order (GLCM, ISZ)	486	5	ROI
Tian et al. 2018	Private	Training	First-order, second-order (GLCM, GLCGM)	510	30	VOI
Hashido et al. 2018	Private	Training (42) + testing (4)	First-order, second-order (GLCM, GLDM, GLRLM, GLSZM, and NGTDM)	91	75	Random forest-based semiautomatic tumor segmentation
Vamvakas et al. 2019	Private	Training	First-order and second-order texture (GLCM, GLRLM)	581	21	VOI
Zhao et al. 2020	Private	Training	First-order and second-order (GLCM, GLRLM, GLSZM, and GLDM)	1072	30	VOI