What is the annual electron and X-ray output constancy vs gantry angle tolerance?

• A. ±1% from baseline
• B. ±0.5% from baseline
• C. ±2% from baseline
• D. ±1.5% from baseline

Answer: (A)

Rotational output stability is what this is testing: how much the beam’s output changes when the gantry points at different angles. You establish a baseline output at a reference angle, then over the year you measure the output at various gantry angles and compare each to that baseline. The annual tolerance is the allowable variation from baseline across those angles, and the standard value used here is plus or minus 1 percent. This reflects the level of precision needed to ensure the dose delivered stays consistent regardless of gantry position, while accounting for typical measurement uncertainties and calibration processes. If a measurement at any angle deviates by more than 1%, that signals a potential drift or calibration issue to address. The other options would either let too much angle-dependent variation slip by or be unrealistically stringent given routine measurement uncertainty.