In annual Gy/mAs testing, which devices are used?

• A. A dosimeter only
• B. A homogeneous phantom only
• C. A dosimeter and a homogeneous phantom
• D. Neither dosimeter nor phantom

Answer: (C)

Gy/mAs testing measures the X-ray unit’s dose output per unit of exposure, using a tissue‑equivalent path to reflect what a patient would receive. To get a meaningful, reproducible result you need both a dosimeter to quantify the actual dose (in Gy) and a homogeneous phantom to simulate patient attenuation and scatter. The dosimeter on its own would read the exposure in free air and wouldn’t account for how tissue reduces and scatters the beam. A phantom alone would give a dose reading only if a detector is present; without a measurement device you can’t quantify Gy per mAs. Together, the dosimeter inside a uniform phantom provides a reliable, patient‑equivalent measurement of output per mAs, which is exactly what annual Gy/mAs testing requires.