Table 1.

Accuracies of the system used to determine setup margins for perpendicular-to-beam (a) and beam-axis (b) directions

(a) Perpendicular to beam direction (lateral)
Displacement of beam axis	≦±0.5 mm
Position of RC	≦±0.5 mm
Position of patient collimator	≦±0.5 mm
Position of MLC	≦±0.5 mm
Displacement of ICs for horizontal and vertical beam courses	≦±0.5 mm
X-ray beam axis from IC	≦±0.5 mm
FPD axis from IC	≦±0.5 mm
Positioning system (image registration) (ΔP)	≦±2 mm
Machining accuracy of RC	≦±0.3 mm
Machining accuracy of patient collimator	≦±0.3 mm
(b) Beam axis direction
CT conversion (2 %) for 15 cm (if 10 cm, ± 2 mm)	≦±3 mm
Range	≦±1 mm
Machining accuracy of RC	≦±0.3 mm
Uniformity of RC material (1 %) for 5 cm	≦±0.5 mm