Course book Advanced Treatment Planning 2018

So …..

The maximum gantry rotation angle is 360 degrees plus the sum of all concavities

This is the VMAT way. It is analogous to the step and shoot technique in static gantry IMRT.

The concavity can be created in one 360 degree rotation plus partial shielding of the beam.

This is the tomotherapy way . Emulating it with a cone-beam MLC means large leaf travel and is wasteful in terms of primary radiation. (Notice, tomotherapy is also wasteful for narrow fan-beams and long target volumes) Courstesy of Markus Alber