Table 2. Residual setup errors between 6D ExacTrac and 3D CBCT for spinal SBRT.

	Region	Number of patient	Directions	Setup error for 6D ExacTrac		Setup error for 3D CBCT		6D ExacTrac vs 3D CBCT
								Difference		p-value of paired t-test
				RMS	SD	RMS	SD	RMS	SD
Chang et al. [11]	Spine	N = 11, n = 16	Translational
			Lateral (x-axis) (mm)	n/a	n/a	n/a	n/a	1.22	1.25	0.875
			Longitudinal (z-axis) (mm)	n/a	n/a	n/a	n/a	0.93	0.94	0.307
			Vertical-(y-axis)(mm)	n/a	n/a	n/a	n/a	1.67	1.65	0.162
			Rotational
			Pitch (x-axis) (°)	n/a	n/a	n/a	n/a	0.54	0.53	0.271
			Roll (z-axis) (°)	n/a	n/a	n/a	n/a	0.40	0.40	0.356
			Yaw (y-axis) (°)	n/a	n/a	n/a	n/a	0.87	0.90	0.896
Oh et al. [12]	Brain	N = 107, n = 138	Translational
			Lateral (x-axis) (mm)	0.20	0.20	0.97	0.65	1.01	0.60	<0.001a
			Longitudinal (z-axis) (mm)	0.24	0.24	0.77	0.77	0.84	0.63	0.425
			Vertical (y-axis) (mm)	0.20	0.20	0.76	0.75	0.76	0.56	0.028a
			Rotational
			Pitch (x-axis) (°)	0.18	0.18	n/a	n/a	n/a	n/a	n/a
			Roll (z-axis) (°)	0.17	0.17	n/a	n/a	n/a	n/a	n/a
			Yaw (y-axis) (°)	0.22	0.22	0.80	0.80	0.82	0.49	0.226
Present Study	Spine	N = 76, n = 268	Translational
			Lateral (x-axis) (mm)	0.40	0.40	1.10	0.81	1.31	0.80	<0.001
			Longitudinal (z-axis) (mm)	0.36	0.36	0.89	0.77	1.06	0.72	<0.001
			Vertical (y-axis) (mm)	0.33	0.33	0.95	0.94	0.87	0.62	0.002
			Rotational
			Pitch (x-axis) (°)	n/a	n/a	n/a	n/a	n/a	n/a	n/a
			Roll (z-axis) (°)	n/a	n/a	n/a	n/a	n/a	n/a	n/a
			Yaw (y-axis) (°)	0.30	0.30	0.46	0.46	0.64	0.44	0.526

Residual setup errors between the 6D ExacTrac and 3D cone-beam computed tomography (CBCT) in spinal stereotactic body radiation therapy (SBRT). ^ap<0.05. N, number of patients; n, number of fractions; RMS, root mean square; SD, standard deviation.