Table 1.

The distribution of studies by imaging modality.

Imaging modality	Number of studies (%)*	References
2D (e.g., kV, MV)	19 (37%)	[26], [61], [75], [76], [81], [82], [84], [85], [86], [87], [88], [89], [90], [91], [92], [93], [94], [95], [96]
2D-2D (e.g., kV-kV, MV-kV)	18 (35%)	[77], [79], [80], [81], [83], [84], [86], [97], [98], [99], [100], [101], [102], [103], [104], [105], [106], [107]
3D (e.g., CBCT, MVCT)	17 (33%)	[61], [73], [74], [78], [80], [82], [83], [84], [108], [109], [110], [111], [112], [113], [114], [115], [116]
SGRT	8 (15%)	[73], [74], [75], [76], [77], [78], [79], [117]
Other (e.g., ultrasound, MRI)	4 (8%)	[118], [119], [120], [121]
Total	52 (100%)

^*The combined modality numbers exceed the total number of studies assessed due to 13 studies including multiple imaging modalities.