What is the monthly cross-hair centering (walkout) tolerance?

• A. 0.5 mm
• B. 2 mm
• C. 1.5 mm
• D. 1 mm

Answer: (D)

This checks how accurately the light-field crosshair aligns with the actual beam center and how stable that alignment is over repeated checks—the walkout you might see when confirming centering. A monthly tolerance of 1 mm means the crosshair must sit within 1 millimeter of the true beam center during the check. That level of precision keeps the light field and radiation field well matched, which is essential for consistent image guidance and accurate targeting in radiography or radiotherapy. Tolerances like 0.5 mm would be stricter than typical monthly QA, while 1.5 mm or 2 mm would allow more misalignment than is generally acceptable for reliable, safe imaging and treatment.