N-VMAT Plan Design and Collision Assessment

The design of the N-VMAT plan was primarily divided into 2 steps. Step 1: set
6 couch angles of 30°, 60°, 90°, 330°, 330°, and 360° referring to Yuan
et al^{22 (link)}
to better compare with the N-VMAT-Cage, and Step 2: design arc size
and ensure that the gantry angle can reach the maximum range without
collision (all arcs are dual arcs). To determine the range of the gantry
angle with different couch angles, the thermoplastic mask of an HCC patient
was buckled on the couch plate of the Elekta Versa HD accelerator (Elekta
Oncology Systems). The gantry was rotated at 6 couch angles. The range of
the gantry angle without collision between the gantry, couch, or
thermoplastic mask is shown in Table 2. All operations conformed
to clinical practice.