What is the monthly distance tolerance between lasers and the front pointer?

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

Answer: (C)

Lasers must consistently line up with the front pointer because that pointer marks the treatment isocenter reference used for patient setup. For monthly QA, the acceptable difference between a laser line and the front pointer is set to 1 mm. This level provides enough precision to maintain accurate isocenter localization across sessions while remaining achievable with routine calibration and measurement methods.

If a laser is more than 1 mm away from the front pointer, it needs adjustment to bring it within tolerance; within 1 mm, it passes the check. The other options would either allow too much deviation (2 mm or 1.5 mm) or be overly strict for a monthly check (0.5 mm).