Table 2.

Comparison between the target registration errors (TREs) for deformation vector fields (DVFs) generated by different methods, using different scan angle schemes. For Elastix, the mask is defined as a region-of-interest (ROI) equal to the limited imaging field-of-view, as determined by the limited projection size (512 × 512 pixels, with 0.8 mm × 0.8 mm each pixel) which is unable to cover the full patient volume. Note for both Elastix registration results (with and without mask), we calculated TRE only within the ROI defined by the mask, to avoid accounting the DVF errors caused by the field-of-view issue. FDK: feldkamp-Davis-Kress (reconstruction algorithm). Def: deformation.

TRE/mm	Scan angle schemes	Elastix w/o mask for def	Elastix w/mask for def	2D-3D Def	2D3D-RegNet
single-view	0°	31.6 ± 22.5	28.4 ± 17.7	6.4 ± 4.7	5.4 ± 4.1
	15°	30.0 ± 21.6	29.3 ± 18.2	5.5 ± 4.1	4.8 ± 3.5
	30°	25.8 ± 17.6	25.0 ± 16.8	5.2 ± 4.0	4.6 ± 3.5
	60°	21.2 ± 15.8	14.0 ± 9.3	4.6 ± 3.7	4.3 ± 3.4
	90°	12.6 ± 8.2	7.0 ± 5.3	5.0 ± 3.9	4.3 ± 3.3
ortho-view	0° (0° each)	10.5 ± 6.8	9.4 ± 6.0	6.0 ± 4.4	5.4 ± 3.7
	15° (7.5° each)	10.7 ± 6.6	9.5 ± 6.2	4.7 ± 3.5	4.8 ± 3.4
	30° (15° each)	11.0 ± 6.8	8.8 ± 6.2	4.3 ± 3.4	4.5 ± 3.4
	60° (30° each)	10.3 ± 6.8	7.3 ± 5.8	4.0 ± 3.3	4.1 ± 3.1
	90° (45° each)	8.5 ± 7.0	5.4 ± 4.6	3.8 ± 3.1	3.9 ± 3.0