Which monthly X-ray output constancy tolerance is specified?

• A. 2%
• B. 1%
• C. 3%
• D. 4%

Answer: (A)

Monthly X-ray output constancy measures how consistently the machine delivers dose from month to month, compared with a baseline established during calibration. The standard tolerance of two percent is used because it hits a practical middle ground: it is tight enough to catch meaningful changes in output that could affect patient dose or image quality, yet broad enough to accommodate normal measurement variability and small, expected fluctuations in the equipment. If the monthly measurement drifts beyond about ±2%, it signals a potential issue that needs maintenance before it impacts dose accuracy. A tolerance of only one percent would be too restrictive given typical dosimeter and setup uncertainties, while larger tolerances like three or four percent could allow significant drift to go unnoticed.