Table 1.

Components contributing to the standard or reduced margins in left–right (LR), superior–inferior (SI) or anterior–posterior (AP) direction. Margins were calculated to ensure coverage of 90% of the target volume with the prescription dose for 90% of patient population.

	Conventional linac workflow/standard margins [mm]			MR-Linac workflow/reduced margins [mm]
	LR	SI	AP	LR	SI	AP
Contouring error	2.0	2.0	2.0	1.0	1.0	1.0
Difference in observed 4D tumour motion between planning and fraction	1.2	1.6	1.4	–	–	–
Total systematic error	2.3	2.6	2.4	1.0	1.0	1.0
Intrafractional baseline drift	1.5	1.7	1.8	1.5	1.7	1.8
Per-fraction localization error	2.0	2.0	2.0	1.0	1.0	1.0
Total random error	2.5	2.6	2.7	1.8	2.0	2.1
Beam penumbra	6.4	6.4	6.4	8.0	8.0	8.0
Total margin	6.4	7.1	6.8	2.8	2.9	2.9