Table 1.

Inter-fraction displacements recorded on units A and B at different periods

	2014 Standard head support			2015 Individual support			2017 Individual support
	VRT	LNG	LAT	VRT	LNG	LAT	VRT	LNG	LAT
UNIT A
Average displacement – M [mm]	- 0.86	0.05	0.05	- 0.47*	- 0.24*	- 0.05	- 0.16*	0.88	0.18
Systematic error – Σ [mm]	0.66	1.04	0.88	0.91	0.79	0.95	0.82	0.59	0.83
Random error – σ [mm]	1.49	1.21	1.37	1.56	1.28	1.38	1.28	1.14	1.2
UNIT B
Average displacement – M [mm]	- 0.60	0.46	- 0.43	- 0.02*	0.51	0.25	- 0.18*	0.46	- 0.02
Systematic error – Σ [mm]	1.09	0.80	0.82	0.92	0.74	0.94	0.93	0.69	0.88
Random error – σ [mm]	1.77	1.83	1.47	1.77	1.22	1.41	1.71	1.56	1.44

LAT = lateral (medial-lateral); LNG = longitudinal (superior-inferior); VRT = vertical (anterior-posterior)

*p < 0.05 (2014 vs. 2015 or 2014 vs. 2017)