Table 4.

Average and standard deviations values for CBCT shifts for all fractions

	CT registered to CBCT			MRI registered to CBCT
	AP (cm)	SI (cm)	LR (cm)	AP (cm)	SI (cm)	LR (cm)
Patient 1	0.21 ± 0.28	0.04 ± 0.25	0.04 ± 0.29	−0.07 ± 0.25	0.11 ± 0.11	0.03 ± 0.27
Patient 2	0.49 ± 0.30	−0.02 ± 0.54	0.07 ± 0.36	0.44 ± 0.28	0.03 ± 0.54	0.04 ± 0.33
Patient 3	0.04 ± 0.61	0.06 ± 0.53	0.06 ± 0.51	0.01 ± 0.76	0.23 ± .58	0.01 ± 0.48
Patient 4	0.10 ± 0.23	0.18 ± 0.24	−0.08 ± 0.26	0.02 ± 0.15	0.02 ± 0.15	0.00 ± 0.00
Patient 5	0.17 ± 0.32	0.28 ± 0.22	−0.06 ± 0.36	0.27 ± 0.47	0.42 ± 0.27	−0.15 ± 0.38
Patient 6	0.26 ± 0.42	0.02 ± 0.24	0.16 ± 0.19	−0.02 ± 0.33	0.10 ± 0.20	0.10 ± 0.18
Patient 7	−0.06 ± 0.49	−0.18 ± 0.88	0.11 ± 0.64	−0.63 ± 0.49	−0.11 ± 0.86	0.15 ± 0.64
Patient 9	−0.33 ± 0.28	−0.10 ± 0.16	0.30 ± 0.25	−0.28 ± 0.29	−0.02 ± 0.11	0.29 ± 0.27
Patient 10	0.36 ± 0.30	0.05 ± 0.15	−0.32 ± 0.31	0.19 ± 0.29	0.04 ± 0.14	−0.31 ± 0.33
M	0.14	0.04	0.03	−0.01	0.09	0.02
Σ	0.24	0.14	0.17	0.31	0.15	0.17
σ	0.38	0.43	0.38	0.41	0.41	0.36
Margin	0.87	0.64	0.69	1.06	0.66	0.68
Margin †	0.85	0.53	0.67	0.84	0.57	0.64

M is the mean group error, Σ is the inter-patient uncertainty and σ is the inter-fraction uncertainty. The sigma values are used to calculate the needed CTV-PTV margin using the van Herk formalism.

^† Margin not including patient 7, see discussion section.