Table 1.

Means and standard deviations (SDs) of the skull-positioning errors measured immediately after treatment

Direction	Fraction number				All fractions	2.11 SD
	1	2	3	4
x (mm)	−0.05 ± 0.47	−0.12 ± 0.42	0.16 ± 0.44	−0.04 ± 0.49	−0.01 ± 0.46a	0.97
y (mm)	−0.07 ± 0.75	−0.11 ± 0.72	−0.23 ± 0.60	−0.02 ± 0.45	−0.11 ±  0.63a	1.30
z (mm)	−0.16 ± 0.54	−0.06 ± 0.38	−0.06 ± 0.41	−0.23 ± 0.29	−0.13 ± 0.42a	0.88
Rx (deg)	0.10 ± 0.42	0.18 ± 0.36	0.06 ± 0.29	0.15 ± 0.29	0.12 ± 0.34
Ry (deg)	0.15 ± 0.38	−0.08 ± 0.51	−0.08 ± 0.41	−0.1 ± 0.35	−0.03 ± 0.42
Rz (deg)	−0.03 ± 0.44	−0.19 ± 0.68	−0.22 ± 0.60	−0.33 ± 0.56	−0.19 ± 0.57

Each error was calculated by the bone-matching procedure available in the on-board cone beam CT system, and therefore, considered as an average positioning error during beam delivery. Mean errors in all fractions are also shown with SDs.

^aPlanning target volume margins were calculated by 2.11 times the SD in x, y and z directions.