Figure 1.

Schematic of the open beam (OB)–closed multileaf collimator (cMLC)–sweeping gap (dMLCgap) tests. The depth d and field size $c_x\times c_y$ are the same for all three cases. The detector (ICH) is placed at the isocenter (iso), perpendicular to the beam. From the above measurements, $R_{\text{cMLC}}$ and $R_{\text{dMLCgap}}$ dose ratios are determined.