FIGURE 2.

Schematics depicting the spot positioning and centering calibration measurement. The leftmost columns show the five different couch positions for performing the irradiation on the DailyQA3 device. $D_0$ is the dose measurement by aligning the ion chamber to the imaging isocenter and the diode to the SI and LR axes. The other four dose measurements are based on $\pm 1.5\mathrm{mm}$ SI and LR couch movements. Based on the couch movement, the position of the detectors relative to the spots are different as can be seen in the illustrations. With $D_0$, $D_{-1.5mmSI}$, and $D_{1.5mmSI}$ measurements, the offset along the SI (or Y direction) direction can be determined based on the dose asymmetry along the $S(0,y)$ curve. Similar idea is also applied to the LR offset (or X‐directions) with $D_0$, $D_{-1.5mmLR}$, and $D_{1.5mmLR}$ measurements and $S(x,0)$ curve.