Figure 3.

Gantry sag. Total magnitude of corrected shift with the gantry angle above and below the test device (i.e., with the gantry in up and down positions) in a one‐dimensional representation. In an attempt to quantify gantry sag, the midpoint value between these extremes was 0.17 mm shifted toward the gantry 180° position. The difference from this midpoint to either extreme was 0.4 mm, leading to the indication that the gantry sag magnitude may be quantified to 0.4 mm.