Table 2.

Mean and standard deviation of BB markers positional variations for the 3D-DCAT beams. Note that Targets were numbered as positional sequence. e.g. Target #1 and #5 represent the farthest targets from the isocenter located in the Y2 direction of linac collimator coordinate system. (Positional mean was calculated with all positive numbers, i.e. the direction of the offset in each image was not taken into account.)

	Positional Difference: Mean (mm) ± Standard Deviation (mm)
	Target #1	Target #2	Target #3	Target #4	Target #5	Total
Arc #1	0.42 ± 0.22	0.58 ± 0.17	0.51 ± 0.16	0.72 ± 0.12	0.77 ± 0.06	0.60 ± 0.20
Arc #2	0.67 ± 0.19	0.73 ± 0.08	0.38 ± 0.27	0.49 ± 0.31	0.54 ± 0.29	0.56 ± 0.27
Arc #3	0.47 ± 0.21	0.66 ± 0.12	0.66 ± 0.07	0.64 ± 0.10	0.78 ± 0.11	0.64 ± 0.16
Arc #4	0.68 ± 0.09	0.57 ± 0.09	0.55 ± 0.12	0.73 ± 0.08	0.78 ± 0.17	0.66 ± 0.14
Total	0.56 ± 0.06	0.63 ± 0.04	0.52 ± 0.09	0.64 ± 0.11	0.71 ± 0.10	0.61 ± 0.20